| 0/0 |
2026/07/31 01:57 |
flow |
moderation |
51m
Results: map[Actionable:true Explanation:### Analysis of the Bug Report
This bug report is **highly consistent, self-contained, and fully actionable**.
The report describes a KASAN slab-use-after-free (UAF) in
`xfs_defer_item_unpause` where a `struct xfs_defer_pending` object (from the
`xfs_defer_pending` slab cache of size 64) is accessed after being freed.
---
### Detailed Walkthrough of the Three Stack Traces
#### 1. Allocation Stack
```
kmem_cache_alloc_noprof+0x2a0/0x5f0 mm/slub.c:4931
xfs_defer_alloc fs/xfs/libxfs/xfs_defer.c:829 [inline]
xfs_defer_add+0x143/0x480 fs/xfs/libxfs/xfs_defer.c:857
...
xfs_alloc_schedule_autoreap+0xb0/0x170 fs/xfs/libxfs/xfs_alloc.c:2727
xrep_newbt_add_blocks+0x239/0x410 fs/xfs/scrub/newbt.c:209
```
* **What happens:** During online repair (`xrep_rmapbt`), the repair code
allocates blocks for a new btree and schedules an autoreap
(`xfs_alloc_schedule_autoreap`).
* **Result:** This schedules a deferred extent free operation, which allocates a
`struct xfs_defer_pending` (`dfp`) object and saves its pointer in
`resv->autoreap.dfp`.
#### 2. Free Stack
```
kmem_cache_free+0x182/0x650 mm/slub.c:6504
xfs_defer_cancel_list fs/xfs/libxfs/xfs_defer.c:504 [inline]
xfs_defer_finish_noroll+0xde4/0x1320 fs/xfs/libxfs/xfs_defer.c:723
xfs_defer_finish+0x1c/0x180 fs/xfs/libxfs/xfs_defer.c:741
xrep_defer_finish+0x16e/0x240 fs/xfs/scrub/repair.c:242
xrep_newbt_alloc_ag_blocks+0x86c/0xcc0 fs/xfs/scrub/newbt.c:316
```
* **What happens:** A subsequent transaction roll/finish (`xrep_defer_finish`)
fails.
* **Result:** The transaction is aborted, forcing a filesystem shutdown. As part
of the abort sequence, `xfs_defer_cancel_list` is called to cancel and free all
pending deferred items, including our `dfp` object.
#### 3. Bad Memory Access Stack
```
xfs_defer_item_unpause+0x116/0x250 fs/xfs/libxfs/xfs_defer.c:1242
xrep_newbt_free+0x3fe/0x5f0 fs/xfs/scrub/newbt.c:520
```
* **What happens:** Because the repair failed, `xrep_newbt_free` is called to
clean up the reservations.
* **Result:** It iterates over the reservations and calls
`xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);`, which invokes
`xfs_defer_item_unpause` on the dangling `resv->autoreap.dfp` pointer.
* **The Crash:** `xfs_defer_item_unpause` attempts to clear the
`XFS_DEFER_PAUSED` flag in `dfp->dfp_flags`:
```c
dfp->dfp_flags &= ~XFS_DEFER_PAUSED;
```
`dfp_flags` is located at offset 60 bytes (480 bits) inside the 64-byte
`struct xfs_defer_pending` object. This perfectly matches the KASAN report:
> Read of size 4 at addr ffff8880443214bc (60 bytes inside of freed 64-byte
region)
---
### Root Cause
When a transaction is aborted and the filesystem is shut down, all pending
deferred items (including paused ones) are cancelled and freed. However, the
reference to the `dfp` in `resv->autoreap.dfp` is not cleared. When the cleanup
path subsequently tries to commit or cancel the autoreap, it dereferences the
dangling `dfp` pointer, causing a use-after-free.
---
### Proposed Fix
Since a transaction abort forces a filesystem shutdown, and all deferred items
are already freed during shutdown, we can safely avoid dereferencing `aarp->dfp`
in `xfs_alloc_commit_autoreap` and `xfs_alloc_cancel_autoreap` if the filesystem
is shut down:
```c
void
xfs_alloc_commit_autoreap(
struct xfs_trans *tp,
struct xfs_alloc_autoreap *aarp)
{
if (xfs_is_shutdown(tp->t_mountp))
return;
if (aarp->dfp)
xfs_defer_item_unpause(tp, aarp->dfp);
}
void
xfs_alloc_cancel_autoreap(
struct xfs_trans *tp,
struct xfs_alloc_autoreap *aarp)
{
struct xfs_defer_pending *dfp = aarp->dfp;
struct xfs_extent_free_item *xefi;
if (xfs_is_shutdown(tp->t_mountp))
return;
if (!dfp)
return;
list_for_each_entry(xefi, &dfp->dfp_work, xefi_list)
xefi->xefi_flags |= XFS_EFI_CANCELLED;
xfs_defer_item_unpause(tp, dfp);
}
```]
|
| 1/1 |
2026/07/31 01:57 |
action |
kernel-checkouter |
0m
Results: map[KernelSrc:/app/workdir/cache/src/ea1ec46165a34622b3d5769ce1a7084d96856f42]
|
| 2/1 |
2026/07/31 01:57 |
action |
kernel-builder |
27m
Results: map[KernelObj:/app/workdir/cache/build/efb990c7b5736ea68587554a874e355bc840a171]
|
| 3/1 |
2026/07/31 02:24 |
action |
codesearch-prepare |
11m
Results: map[Index:codesearch-index]
|
| 4/1 |
2026/07/31 02:35 |
agent |
expert |
13m
Model:
Results:
Instruction: You are an experienced Linux kernel developer tasked with determining if the given kernel bug
report is actionable or not. Actionable means that it contains enough info to root cause
the underlying bug, and that the report is self-consistent and makes sense, rather than
e.g. a one-off nonsensical crash induced by a previous memory corruption.
The bug report is about a use-after-free bug generated by KASAN tool.
It should contain 3 stack traces: the bad memory access stack, the heap block allocation stack,
and the heap block free stack. If the report does not contain 3 stacks, it's not actionable.
All 3 stack traces should be related to the same object type,
and usually be in the same kernel subsystem (at least leaf stack frames).
An example of an actionable and consistent report would be: first access stack relates
to an access to a field of struct Foo, allocation/free stacks relate to allocation/free
of the struct Foo.
In inconsistent/nonsensical reports an access may be to a struct Foo, but allocation
stack allocates a different structure in a different subsystem.
Look for other suspicious signals/inconsistencies that can make this report hard to
debug/understand.
In the final reply explain why you think the report is self-consistent and actionable,
or why it's inconsistent and/or not actionable.
Use the provided tools to confirm any assumptions, variables/fields being accessed, etc.
Don't make assumptions about the kernel source code (it may be different from what you assume it is).
Extensively use the provided code access tools (codesearch-*, git-*, grepper, etc)
to examine the actual source code, and confirm any assumptions.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt:
The bug report is:
loop0: detected capacity change from 0 to 32768
=======================================================
WARNING: The mand mount option has been deprecated and
and is ignored by this kernel. Remove the mand
option from the mount to silence this warning.
=======================================================
XFS (loop0): Mounting V5 Filesystem bfdc47fc-10d8-4eed-a562-11a831b3f791
XFS (loop0): Ending clean mount
XFS (loop0): Quotacheck needed: Please wait.
XFS (loop0): Quotacheck: Done.
loop0: detected capacity change from 32768 to 0
==================================================================
BUG: KASAN: slab-use-after-free in xfs_defer_item_unpause+0x116/0x250 fs/xfs/libxfs/xfs_defer.c:1242
Read of size 4 at addr ffff8880443214bc by task syz.0.0/5326
CPU: 0 UID: 0 PID: 5326 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description+0x55/0x1e0 mm/kasan/report.c:378
print_report+0x58/0x70 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
xfs_defer_item_unpause+0x116/0x250 fs/xfs/libxfs/xfs_defer.c:1242
xrep_newbt_free+0x3fe/0x5f0 fs/xfs/scrub/newbt.c:520
xrep_rmap_build_new_tree+0x5b5/0x8c0 fs/xfs/scrub/rmap_repair.c:1447
xrep_rmapbt+0x78/0xb0 fs/xfs/scrub/rmap_repair.c:1722
xrep_attempt+0x184/0x7c0 fs/xfs/scrub/repair.c:78
xfs_scrub_metadata+0xce4/0x1910 fs/xfs/scrub/scrub.c:747
xfs_ioc_scrubv_metadata+0x7ac/0xb70 fs/xfs/scrub/scrub.c:981
xfs_file_ioctl+0x916/0x1590 fs/xfs/xfs_ioctl.c:1308
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7335b9de99
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7336b4cfe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f7335e25fa0 RCX: 00007f7335b9de99
RDX: 0000200000000000 RSI: 00000000c0285840 RDI: 0000000000000007
RBP: 00007f7335c33eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7335e26038 R14: 00007f7335e25fa0 R15: 00007ffde61731e8
</TASK>
Allocated by task 5326:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
unpoison_slab_object mm/kasan/common.c:340 [inline]
__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4584 [inline]
slab_alloc_node mm/slub.c:4917 [inline]
kmem_cache_alloc_noprof+0x2a0/0x5f0 mm/slub.c:4931
xfs_defer_alloc fs/xfs/libxfs/xfs_defer.c:829 [inline]
xfs_defer_add+0x143/0x480 fs/xfs/libxfs/xfs_defer.c:857
xfs_extent_free_defer_add+0x1bf/0x3b0 fs/xfs/xfs_extfree_item.c:507
xfs_defer_extent_free+0x2a8/0x400 fs/xfs/libxfs/xfs_alloc.c:2682
xfs_alloc_schedule_autoreap+0xb0/0x170 fs/xfs/libxfs/xfs_alloc.c:2727
xrep_newbt_add_blocks+0x239/0x410 fs/xfs/scrub/newbt.c:209
xrep_newbt_alloc_ag_blocks+0x81e/0xcc0 fs/xfs/scrub/newbt.c:309
xrep_rmap_try_reserve+0x1f4/0x800 fs/xfs/scrub/rmap_repair.c:1068
xrep_rmap_reserve_space+0x19a/0x470 fs/xfs/scrub/rmap_repair.c:1162
xrep_rmap_build_new_tree+0x3d9/0x8c0 fs/xfs/scrub/rmap_repair.c:1369
xrep_rmapbt+0x78/0xb0 fs/xfs/scrub/rmap_repair.c:1722
xrep_attempt+0x184/0x7c0 fs/xfs/scrub/repair.c:78
xfs_scrub_metadata+0xce4/0x1910 fs/xfs/scrub/scrub.c:747
xfs_ioc_scrubv_metadata+0x7ac/0xb70 fs/xfs/scrub/scrub.c:981
xfs_file_ioctl+0x916/0x1590 fs/xfs/xfs_ioctl.c:1308
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Freed by task 5326:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2677 [inline]
slab_free mm/slub.c:6377 [inline]
kmem_cache_free+0x182/0x650 mm/slub.c:6504
xfs_defer_cancel_list fs/xfs/libxfs/xfs_defer.c:504 [inline]
xfs_defer_finish_noroll+0xde4/0x1320 fs/xfs/libxfs/xfs_defer.c:723
xfs_defer_finish+0x1c/0x180 fs/xfs/libxfs/xfs_defer.c:741
xrep_defer_finish+0x16e/0x240 fs/xfs/scrub/repair.c:242
xrep_newbt_alloc_ag_blocks+0x86c/0xcc0 fs/xfs/scrub/newbt.c:316
xrep_rmap_try_reserve+0x1f4/0x800 fs/xfs/scrub/rmap_repair.c:1068
xrep_rmap_reserve_space+0x19a/0x470 fs/xfs/scrub/rmap_repair.c:1162
xrep_rmap_build_new_tree+0x3d9/0x8c0 fs/xfs/scrub/rmap_repair.c:1369
xrep_rmapbt+0x78/0xb0 fs/xfs/scrub/rmap_repair.c:1722
xrep_attempt+0x184/0x7c0 fs/xfs/scrub/repair.c:78
xfs_scrub_metadata+0xce4/0x1910 fs/xfs/scrub/scrub.c:747
xfs_ioc_scrubv_metadata+0x7ac/0xb70 fs/xfs/scrub/scrub.c:981
xfs_file_ioctl+0x916/0x1590 fs/xfs/xfs_ioctl.c:1308
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
The buggy address belongs to the object at ffff888044321480
which belongs to the cache xfs_defer_pending of size 64
The buggy address is located 60 bytes inside of
freed 64-byte region [ffff888044321480, ffff8880443214c0)
The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff8880443216c0 pfn:0x44321
flags: 0x4fff00000000200(workingset|node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000200 ffff888030ba9c80 ffff8880305a9ac8 ffff8880305a9ac8
raw: ffff8880443216c0 00000008002a0012 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2c40(GFP_NOFS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 12, tgid 12 (kworker/u4:0), ts 94710883881, free_ts 90574972561
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1859
prep_new_page mm/page_alloc.c:1867 [inline]
get_page_from_freelist+0x21fa/0x2270 mm/page_alloc.c:3946
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5304
alloc_slab_page mm/slub.c:3266 [inline]
allocate_slab+0x79/0x5e0 mm/slub.c:3380
new_slab mm/slub.c:3426 [inline]
refill_objects+0x2d5/0x350 mm/slub.c:7310
refill_sheaf mm/slub.c:2804 [inline]
__pcs_replace_empty_main+0x2bf/0x6b0 mm/slub.c:4675
alloc_from_pcs mm/slub.c:4773 [inline]
slab_alloc_node mm/slub.c:4905 [inline]
kmem_cache_alloc_noprof+0x382/0x5f0 mm/slub.c:4931
xfs_defer_alloc fs/xfs/libxfs/xfs_defer.c:829 [inline]
xfs_defer_add+0x143/0x480 fs/xfs/libxfs/xfs_defer.c:857
xfs_bmap_add_extent_hole_real+0xd61/0x1a40 fs/xfs/libxfs/xfs_bmap.c:2782
xfs_bmapi_allocate+0x248c/0x2f20 fs/xfs/libxfs/xfs_bmap.c:3975
xfs_bmapi_write+0x843/0x1330 fs/xfs/libxfs/xfs_bmap.c:4265
xfs_dquot_disk_alloc+0x4af/0xae0 fs/xfs/xfs_dquot.c:381
xfs_qm_dqread+0xfe/0x520 fs/xfs/xfs_dquot.c:720
xfs_qm_dqget+0x18a/0x3d0 fs/xfs/xfs_dquot.c:922
xfs_qm_quotacheck_dqadjust+0xdd/0x5a0 fs/xfs/xfs_qm.c:1260
xfs_qm_dqusage_adjust+0x4ad/0x670 fs/xfs/xfs_qm.c:1389
page last free pid 5284 tgid 5284 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1406 [inline]
__free_frozen_pages+0xc1e/0xd10 mm/page_alloc.c:2950
__slab_free+0x274/0x2c0 mm/slub.c:5741
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x99/0x100 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4584 [inline]
slab_alloc_node mm/slub.c:4917 [inline]
kmem_cache_alloc_node_noprof+0x355/0x610 mm/slub.c:4989
__alloc_skb+0x1d7/0x7a0 net/core/skbuff.c:704
alloc_skb include/linux/skbuff.h:1384 [inline]
nlmsg_new include/net/netlink.h:1055 [inline]
netlink_ack+0x136/0xb30 net/netlink/af_netlink.c:2493
netlink_rcv_skb+0x2a4/0x4a0 net/netlink/af_netlink.c:2562
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x7bb/0x940 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec+0x13a/0x180 net/socket.c:775
__sock_sendmsg net/socket.c:790 [inline]
__sys_sendto+0x408/0x5a0 net/socket.c:2252
__do_sys_sendto net/socket.c:2259 [inline]
__se_sys_sendto net/socket.c:2255 [inline]
__x64_sys_sendto+0xde/0x100 net/socket.c:2255
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Memory state around the buggy address:
ffff888044321380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888044321400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888044321480: fa fb fb fb fb fb fb fb fc fc fc fc fa fb fb fb
^
ffff888044321500: fb fb fb fb fc fc fc fc fa fb fb fb fb fb fb fb
ffff888044321580: fc fc fc fc fa fb fb fb fb fb fb fb fc fc fc fc
==================================================================
Reply: ### Analysis of the Bug Report
This bug report is **highly consistent, self-contained, and fully actionable**.
The report describes a KASAN slab-use-after-free (UAF) in `xfs_defer_item_unpause` where a `struct xfs_defer_pending` object (from the `xfs_defer_pending` slab cache of size 64) is accessed after being freed.
---
### Detailed Walkthrough of the Three Stack Traces
#### 1. Allocation Stack
```
kmem_cache_alloc_noprof+0x2a0/0x5f0 mm/slub.c:4931
xfs_defer_alloc fs/xfs/libxfs/xfs_defer.c:829 [inline]
xfs_defer_add+0x143/0x480 fs/xfs/libxfs/xfs_defer.c:857
...
xfs_alloc_schedule_autoreap+0xb0/0x170 fs/xfs/libxfs/xfs_alloc.c:2727
xrep_newbt_add_blocks+0x239/0x410 fs/xfs/scrub/newbt.c:209
```
* **What happens:** During online repair (`xrep_rmapbt`), the repair code allocates blocks for a new btree and schedules an autoreap (`xfs_alloc_schedule_autoreap`).
* **Result:** This schedules a deferred extent free operation, which allocates a `struct xfs_defer_pending` (`dfp`) object and saves its pointer in `resv->autoreap.dfp`.
#### 2. Free Stack
```
kmem_cache_free+0x182/0x650 mm/slub.c:6504
xfs_defer_cancel_list fs/xfs/libxfs/xfs_defer.c:504 [inline]
xfs_defer_finish_noroll+0xde4/0x1320 fs/xfs/libxfs/xfs_defer.c:723
xfs_defer_finish+0x1c/0x180 fs/xfs/libxfs/xfs_defer.c:741
xrep_defer_finish+0x16e/0x240 fs/xfs/scrub/repair.c:242
xrep_newbt_alloc_ag_blocks+0x86c/0xcc0 fs/xfs/scrub/newbt.c:316
```
* **What happens:** A subsequent transaction roll/finish (`xrep_defer_finish`) fails.
* **Result:** The transaction is aborted, forcing a filesystem shutdown. As part of the abort sequence, `xfs_defer_cancel_list` is called to cancel and free all pending deferred items, including our `dfp` object.
#### 3. Bad Memory Access Stack
```
xfs_defer_item_unpause+0x116/0x250 fs/xfs/libxfs/xfs_defer.c:1242
xrep_newbt_free+0x3fe/0x5f0 fs/xfs/scrub/newbt.c:520
```
* **What happens:** Because the repair failed, `xrep_newbt_free` is called to clean up the reservations.
* **Result:** It iterates over the reservations and calls `xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);`, which invokes `xfs_defer_item_unpause` on the dangling `resv->autoreap.dfp` pointer.
* **The Crash:** `xfs_defer_item_unpause` attempts to clear the `XFS_DEFER_PAUSED` flag in `dfp->dfp_flags`:
```c
dfp->dfp_flags &= ~XFS_DEFER_PAUSED;
```
`dfp_flags` is located at offset 60 bytes (480 bits) inside the 64-byte `struct xfs_defer_pending` object. This perfectly matches the KASAN report:
> Read of size 4 at addr ffff8880443214bc (60 bytes inside of freed 64-byte region)
---
### Root Cause
When a transaction is aborted and the filesystem is shut down, all pending deferred items (including paused ones) are cancelled and freed. However, the reference to the `dfp` in `resv->autoreap.dfp` is not cleared. When the cleanup path subsequently tries to commit or cancel the autoreap, it dereferences the dangling `dfp` pointer, causing a use-after-free.
---
### Proposed Fix
Since a transaction abort forces a filesystem shutdown, and all deferred items are already freed during shutdown, we can safely avoid dereferencing `aarp->dfp` in `xfs_alloc_commit_autoreap` and `xfs_alloc_cancel_autoreap` if the filesystem is shut down:
```c
void
xfs_alloc_commit_autoreap(
struct xfs_trans *tp,
struct xfs_alloc_autoreap *aarp)
{
if (xfs_is_shutdown(tp->t_mountp))
return;
if (aarp->dfp)
xfs_defer_item_unpause(tp, aarp->dfp);
}
void
xfs_alloc_cancel_autoreap(
struct xfs_trans *tp,
struct xfs_alloc_autoreap *aarp)
{
struct xfs_defer_pending *dfp = aarp->dfp;
struct xfs_extent_free_item *xefi;
if (xfs_is_shutdown(tp->t_mountp))
return;
if (!dfp)
return;
list_for_each_entry(xefi, &dfp->dfp_work, xefi_list)
xefi->xefi_flags |= XFS_EFI_CANCELLED;
xfs_defer_item_unpause(tp, dfp);
}
```
|
| 5/2 |
2026/07/31 02:35 |
llm |
expert |
0m
Model:
Tokens:
input: 9633
output: 44
thoughts: 1369
Thoughts: **Analyzing the XFS Kernel Bug Report**
Alright, let's dive into this kernel bug report and see if it's actionable. It appears we have a KASAN slab-use-after-free, specifically in the `xfs_defer_item_unpause` function. The error occurs at `fs/xfs/libxfs/xfs_defer.c:1242`, which is a read of size 4 at a specific memory address that's within a freed 64-byte region belonging to the `xfs_defer_pending` cache.
Now, let's break down the stack traces to understand the flow:
* **The Bad Memory Access Stack:** This shows `xfs_defer_item_unpause` as the culprit, followed by calls to functions involved in the XFS metadata scrubber (`xrep_newbt_free`, `xrep_rmap_build_new_tree`, etc.). Ultimately it seems that this is caused by the ioc calling the scrub metadata function.
* **The Allocation Stack:** Here, we see the object being allocated through `kmem_cache_alloc_noprof` and then added to the defer list, ultimately being allocated as part of the scrub repair processes.
* **The Free Stack:** Finally, the object gets freed via `kmem_cache_free`. This stack also runs through the `xfs_defer_cancel_list` which indicates that this is a defer mechanism operation, again, during the scrubbing process.
So, all three stacks point towards the XFS file system, especially scrub/repair and defer operations. That is an interesting correlation. This means that a memory leak could be related to the xfs operations.
To get a better handle on this, I'll need to go to the source code and look at the specifics. Specifically, I'll be checking `fs/xfs/libxfs/xfs_defer.c` around line 1242, and `fs/xfs/scrub/newbt.c` around line 520, to see how the object is being used after it's supposed to be freed. This will give me some ideas about the race condition that causes this bug.
|
| 6/2 |
2026/07/31 02:36 |
tool |
read-file |
0m
Args: map[File:fs/xfs/libxfs/xfs_defer.c FirstLine:1220 LineCount:40]
Results: map[Contents:1220: xfs_defer_item_pause(
1221: struct xfs_trans *tp,
1222: struct xfs_defer_pending *dfp)
1223: {
1224: ASSERT(!(dfp->dfp_flags & XFS_DEFER_PAUSED));
1225:
1226: dfp->dfp_flags |= XFS_DEFER_PAUSED;
1227:
1228: trace_xfs_defer_item_pause(tp->t_mountp, dfp);
1229: }
1230:
1231: /*
1232: * Release a paused deferred work item so that it will be finished during the
1233: * next transaction roll.
1234: */
1235: void
1236: xfs_defer_item_unpause(
1237: struct xfs_trans *tp,
1238: struct xfs_defer_pending *dfp)
1239: {
1240: ASSERT(dfp->dfp_flags & XFS_DEFER_PAUSED);
1241:
1242: dfp->dfp_flags &= ~XFS_DEFER_PAUSED;
1243:
1244: trace_xfs_defer_item_unpause(tp->t_mountp, dfp);
1245: }
]
|
| 7/2 |
2026/07/31 02:36 |
llm |
expert |
0m
Model:
Tokens:
input: 11924
output: 24
thoughts: 63
Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective:
**Diving into the `xfs_defer_item_unpause` Function**
Right, so `xfs_defer_item_unpause` is poking around at `dfp->dfp_flags`. That's interesting, I need to understand what's happening there. I need to refresh my memory on the structure of `struct xfs_defer_pending`. Let's see...I think `codesearch-struct-layout` or `codesearch-definition-source` should give me the exact layout of that structure, so I can see what these flags are and what `xfs_defer_item_unpause` is doing with them. This is likely related to pausing or unpausing deferred operations within the XFS filesystem. Let me look at the code and refresh my memory.
|
| 8/2 |
2026/07/31 02:36 |
tool |
codesearch-struct-layout |
0m
Args: map[Name:xfs_defer_pending]
Results: map[Fields:[map[Name:dfp_list OffsetBits:0 SizeBits:128] map[Name:dfp_work OffsetBits:128 SizeBits:128] map[Name:dfp_intent OffsetBits:256 SizeBits:64] map[Name:dfp_done OffsetBits:320 SizeBits:64] map[Name:dfp_ops OffsetBits:384 SizeBits:64] map[Name:dfp_count OffsetBits:448 SizeBits:32] map[Name:dfp_flags OffsetBits:480 SizeBits:32]]]
|
| 9/2 |
2026/07/31 02:36 |
llm |
expert |
5m
Model:
Tokens:
input: 12369
output: 40
thoughts: 163
Thoughts: **Precise Diagnosis of a Memory Corruption Bug**
Okay, so `dfp_flags` is sitting pretty far out there, at bit offset 480, which translates to a whopping 60 bytes! The crash report, specifically the buggy address, confirms this; it's right at 60 bytes within a 64-byte freed region `[ffff888044321480, ffff8880443214c0)`. Excellent! This means the offset is exactly what we expected, and the code is hitting `dfp->dfp_flags &= ~XFS_DEFER_PAUSED;` at line 1242, which corroborates the findings. The consistency is impressive. We've got a tight confirmation here. Now, let's turn our attention to `fs/xfs/scrub/newbt.c`, specifically around line 520, to understand the context of this access.
|
| 10/2 |
2026/07/31 02:42 |
tool |
read-file |
0m
Args: map[File:fs/xfs/scrub/newbt.c FirstLine:500 LineCount:40]
Results: map[Contents: 500:
501: freed += ret;
502: if (freed >= XREP_MAX_ITRUNCATE_EFIS) {
503: error = xrep_defer_finish(sc);
504: if (error)
505: goto junkit;
506: freed = 0;
507: }
508: }
509:
510: if (freed)
511: error = xrep_defer_finish(sc);
512:
513: junkit:
514: /*
515: * If we still have reservations attached to @newbt, cleanup must have
516: * failed and the filesystem is about to go down. Clean up the incore
517: * reservations and try to commit to freeing the space we used.
518: */
519: list_for_each_entry_safe(resv, n, &xnr->resv_list, list) {
520: xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);
521: list_del(&resv->list);
522: xfs_perag_put(resv->pag);
523: kfree(resv);
524: }
525:
526: if (sc->ip) {
527: kmem_cache_free(xfs_ifork_cache, xnr->ifake.if_fork);
528: xnr->ifake.if_fork = NULL;
529: }
530:
531: return error;
532: }
533:
534: /*
535: * Free all the accounting info and unused disk space allocations after
536: * committing a new btree.
537: */
538: int
539: xrep_newbt_commit(
]
|
| 11/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 13350
output: 34
thoughts: 66
Thoughts: **Analyzing the `xrep_newbt_free` Function**
Okay, so I'm digging into this `xrep_newbt_free` function, and I've hit a potential point of interest at line 520. It looks like `xrep_newbt_free` is calling `xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap)`. That's interesting, and I immediately want to understand what's happening there. Autoreaping is always a key area to scrutinize in XFS, so itās worth investigating. I need to get a clear picture of what `xfs_alloc_commit_autoreap` is actually doing within the larger context. My next step, naturally, is to locate the definition of `xfs_alloc_commit_autoreap` so I can see its implementation and understand the logic flow. Let's see what's going on underneath.
|
| 12/2 |
2026/07/31 02:42 |
tool |
codesearch-find-references |
0m
Args: map[IncludeSnippetLines:10 Name:xfs_alloc_commit_autoreap]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:xrep_newbt_free SourceFile:fs/xfs/scrub/newbt.c SourceLine:520 SourceSnippet: 510: if (freed)
511: error = xrep_defer_finish(sc);
512:
513: junkit:
514: /*
515: * If we still have reservations attached to @newbt, cleanup must have
516: * failed and the filesystem is about to go down. Clean up the incore
517: * reservations and try to commit to freeing the space we used.
518: */
519: list_for_each_entry_safe(resv, n, &xnr->resv_list, list) {
520: xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);
521: list_del(&resv->list);
522: xfs_perag_put(resv->pag);
523: kfree(resv);
524: }
525:
526: if (sc->ip) {
527: kmem_cache_free(xfs_ifork_cache, xnr->ifake.if_fork);
528: xnr->ifake.if_fork = NULL;
529: }
530:
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:xrep_newbt_free_extent SourceFile:fs/xfs/scrub/newbt.c SourceLine:436 SourceSnippet: 426: int error;
427:
428: if (!btree_committed || resv->used == 0) {
429: /*
430: * If we're not committing a new btree or we didn't use the
431: * space reservation, let the existing EFI free the entire
432: * space extent.
433: */
434: trace_xrep_newbt_free_blocks(resv->pag, free_agbno, free_aglen,
435: xnr->oinfo.oi_owner);
436: xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);
437: return 1;
438: }
439:
440: /*
441: * We used space and committed the btree. Cancel the autoreap, remove
442: * the written blocks from the reservation, and possibly log a new EFI
443: * to free any unused reservation space.
444: */
445: xfs_alloc_cancel_autoreap(sc->tp, &resv->autoreap);
446: free_agbno += resv->used;
]] TruncatedOutput:false]
|
| 13/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 14472
output: 24
thoughts: 47
Thoughts: Okay, here's my interpretation of that thought process, as if it were my own:
**Investigating `xfs_alloc_commit_autoreap`**
Right, let's get down to brass tacks. I need to understand what `xfs_alloc_commit_autoreap` *actually* does. It's a key function, and I need a clear understanding of its operation. I'm going to track down its definition, and the best way to do that is probably a focused search. Time to pull out the big guns. Let's fire up `grepper` or `codesearch-find-references`. A straight search for `"xfs_alloc_commit_autoreap"` should give me what I need. I'm hoping I can easily see where it's defined and, ideally, where it's *used*. Getting references will give me that context and help me quickly understand its purpose. This is a good starting point. From there, I can drill deeper if necessary.
|
| 14/2 |
2026/07/31 02:42 |
tool |
grepper |
0m
Args: map[Expression:void xfs_alloc_commit_autoreap]
Results: map[Output:fs/xfs/libxfs/xfs_alloc.h=277=void xfs_alloc_cancel_autoreap(struct xfs_trans *tp,
fs/xfs/libxfs/xfs_alloc.h-278- struct xfs_alloc_autoreap *aarp);
fs/xfs/libxfs/xfs_alloc.h:279:void xfs_alloc_commit_autoreap(struct xfs_trans *tp,
fs/xfs/libxfs/xfs_alloc.h-280- struct xfs_alloc_autoreap *aarp);
]
|
| 15/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 14917
output: 48
thoughts: 33
Thoughts: Okay, here's my interpretation of what's going through my mind as I approach `fs/xfs/libxfs/xfs_alloc.c` and specifically focus on `xfs_alloc_commit_autoreap`:
**Diving into xfs_alloc_commit_autoreap**
Alright, let's get down to brass tacks. I'm heading into `xfs_alloc.c` ā a core file, obviously, dealing with space allocation within the XFS filesystem. And my specific target? `xfs_alloc_commit_autoreap`. This is where the magic (or perhaps the debugging pain!) of automatic reclamation likely happens, and I want to understand exactly what's going on. I'm expecting this function deals with the cleanup of allocated blocks, perhaps after a crash, a transaction commit, or simply as part of regular filesystem housekeeping. I'm keen to see if it's got any unexpected behaviors. Let's dig in and figure out how it works!
|
| 16/2 |
2026/07/31 02:42 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/xfs/libxfs/xfs_alloc.c Name:xfs_alloc_commit_autoreap]
Results: map[SourceCode:2766: /*
2767: * Commit automatic freeing of unwritten space in the filesystem.
2768: *
2769: * This unpauses an earlier _schedule_autoreap and commits to freeing the
2770: * allocated space. Call this if none of the reserved space was used.
2771: */
2772: void
2773: xfs_alloc_commit_autoreap(
2774: struct xfs_trans *tp,
2775: struct xfs_alloc_autoreap *aarp)
2776: {
2777: if (aarp->dfp)
2778: xfs_defer_item_unpause(tp, aarp->dfp);
2779: }
SourceFile:fs/xfs/libxfs/xfs_alloc.c]
|
| 17/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 15457
output: 48
thoughts: 96
Thoughts: **XFS Allocation Commit Autoreap Conundrum**
Alright, let's break this down. So, `xfs_alloc_commit_autoreap` is calling `xfs_defer_item_unpause` with `aarp->dfp` as an argument if `aarp->dfp` is valid. Okay, makes sense so far. Now, the question is, where does `aarp->dfp` get set? We need to trace this back. The obvious next step is to examine the codebase for where this `aarp->dfp` is assigned. Specifically, since we're dealing with autoreap, and the pointer `dfp` itself, I'll search in `fs/xfs/libxfs/xfs_alloc.c` for instances of either "autoreap" or "dfp". That should lead us directly to the initialization and usage of this crucial deferral pointer. This is likely where the core of the behavior lies.
|
| 18/2 |
2026/07/31 02:42 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/xfs/libxfs/xfs_alloc.c Name:xfs_alloc_schedule_autoreap]
Results: map[SourceCode:2701: /*
2702: * Set up automatic freeing of unwritten space in the filesystem.
2703: *
2704: * This function attached a paused deferred extent free item to the
2705: * transaction. Pausing means that the EFI will be logged in the next
2706: * transaction commit, but the pending EFI will not be finished until the
2707: * pending item is unpaused.
2708: *
2709: * If the system goes down after the EFI has been persisted to the log but
2710: * before the pending item is unpaused, log recovery will find the EFI, fail to
2711: * find the EFD, and free the space.
2712: *
2713: * If the pending item is unpaused, the next transaction commit will log an EFD
2714: * without freeing the space.
2715: *
2716: * Caller must ensure that the tp, fsbno, len, oinfo, and resv flags of the
2717: * @args structure are set to the relevant values.
2718: */
2719: int
2720: xfs_alloc_schedule_autoreap(
2721: const struct xfs_alloc_arg *args,
2722: unsigned int free_flags,
2723: struct xfs_alloc_autoreap *aarp)
2724: {
2725: int error;
2726:
2727: error = xfs_defer_extent_free(args->tp, args->fsbno, args->len,
2728: &args->oinfo, args->resv, free_flags, &aarp->dfp);
2729: if (error)
2730: return error;
2731:
2732: xfs_defer_item_pause(args->tp, aarp->dfp);
2733: return 0;
2734: }
SourceFile:fs/xfs/libxfs/xfs_alloc.c]
|
| 19/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 16382
output: 40
thoughts: 629
Thoughts: **Analyzing XFS Deferred Extent Freeing and its Interaction with Scrubbing**
Okay, so I'm tracing the execution path of deferred extent freeing in XFS, specifically focusing on how it relates to the autoreap mechanism. I see that `xfs_alloc_schedule_autoreap` calls `xfs_defer_extent_free`, which ultimately gives us the `aarp->dfp` pointer. Then, `xfs_defer_item_pause` is called on that `dfp`. Alright, let me quickly review the allocation side of things.
I've traced this allocation stack: `kmem_cache_alloc_noprof` -> `xfs_defer_alloc` -> `xfs_defer_add` -> `xfs_extent_free_defer_add` -> `xfs_defer_extent_free` -> `xfs_alloc_schedule_autoreap` -> `xrep_newbt_add_blocks`. So, `aarp->dfp` is allocated and paused within `xrep_newbt_add_blocks`. Got it. That's the setup.
Now, let's switch gears and examine the freeing side. From the looks of it, it's called after the block is allocated and used.
I've identified the freeing stack: `kmem_cache_free` -> `xfs_defer_cancel_list` -> `xfs_defer_finish_noroll` -> `xfs_defer_finish` -> `xrep_defer_finish`. Wait a minute, what's this? `xrep_newbt_alloc_ag_blocks` calls `xrep_defer_finish(sc)`. Okay, that's interesting and could be the crux of whatever issue I'm looking at. I'll need to double-check this in the `fs/xfs/scrub/newbt.c` file around line 316.
|
| 20/2 |
2026/07/31 02:42 |
tool |
read-file |
0m
Args: map[File:fs/xfs/scrub/newbt.c FirstLine:290 LineCount:40]
Results: map[Contents: 290: error = xnr->alloc_vextent(sc, &args, xnr->alloc_hint);
291: else
292: error = xfs_alloc_vextent_near_bno(&args,
293: xnr->alloc_hint);
294: if (error)
295: return error;
296: if (args.fsbno == NULLFSBLOCK)
297: return -ENOSPC;
298:
299: agno = XFS_FSB_TO_AGNO(mp, args.fsbno);
300: if (agno != pag_agno(sc->sa.pag)) {
301: ASSERT(agno == pag_agno(sc->sa.pag));
302: return -EFSCORRUPTED;
303: }
304:
305: trace_xrep_newbt_alloc_ag_blocks(sc->sa.pag,
306: XFS_FSB_TO_AGBNO(mp, args.fsbno), args.len,
307: xnr->oinfo.oi_owner);
308:
309: error = xrep_newbt_add_blocks(xnr, sc->sa.pag, &args);
310: if (error)
311: return error;
312:
313: nr_blocks -= args.len;
314: xnr->alloc_hint = args.fsbno + args.len;
315:
316: error = xrep_defer_finish(sc);
317: if (error)
318: return error;
319: }
320:
321: return 0;
322: }
323:
324: /* Don't let our allocation hint take us beyond EOFS */
325: static inline void
326: xrep_newbt_validate_file_alloc_hint(
327: struct xrep_newbt *xnr)
328: {
329: struct xfs_scrub *sc = xnr->sc;
]
|
| 21/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 18086
output: 43
thoughts: 143
Thoughts: **Debugging a Potential Resource Leak**
Okay, so I'm digging into this code and trying to understand this allocation and deallocation process. I see that `xrep_newbt_alloc_ag_blocks` is calling `xrep_newbt_add_blocks`, which then sets up the autoreap using `dfp` and pauses it. Makes sense so far. But then it calls `xrep_defer_finish(sc)`. The confusing bit is why `xrep_defer_finish(sc)` seems to be freeing that `dfp`? That doesn't feel right. I need to trace this. Let's start by looking into `xfs_defer_finish_noroll` and `xfs_defer_cancel_list` to see how those are handling deferred operations. I know the code pretty well, so I'm going to jump into `fs/xfs/libxfs/xfs_defer.c` and take a look around line 723 and 504. I need to figure out the ownership and lifecycle of that `dfp` and ensure there isn't a premature release. This smells like a possible resource leak.
|
| 22/2 |
2026/07/31 02:42 |
tool |
read-file |
0m
Args: map[File:fs/xfs/libxfs/xfs_defer.c FirstLine:490 LineCount:30]
Results: map[Contents: 490: */
491: static void
492: xfs_defer_cancel_list(
493: struct xfs_mount *mp,
494: struct list_head *dop_list)
495: {
496: struct xfs_defer_pending *dfp;
497: struct xfs_defer_pending *pli;
498:
499: /*
500: * Free the pending items. Caller should already have arranged
501: * for the intent items to be released.
502: */
503: list_for_each_entry_safe(dfp, pli, dop_list, dfp_list)
504: xfs_defer_pending_cancel_work(mp, dfp);
505: }
506:
507: static inline void
508: xfs_defer_relog_intent(
509: struct xfs_trans *tp,
510: struct xfs_defer_pending *dfp)
511: {
512: struct xfs_log_item *lip;
513:
514: xfs_defer_create_done(tp, dfp);
515:
516: lip = dfp->dfp_ops->relog_intent(tp, dfp->dfp_intent, dfp->dfp_done);
517: if (lip) {
518: xfs_trans_add_item(tp, lip);
519: set_bit(XFS_LI_DIRTY, &lip->li_flags);
]
|
| 23/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 18997
output: 43
thoughts: 35
Thoughts: Here's my take on those lines of code, focusing on what I'd be looking at if I were digging into this:
**Analyzing `xfs_defer_pending_cancel_work` and `xfs_defer_finish_noroll`**
Okay, so I need to get my head around how these deferred operations are handled within XFS, specifically around line 723. Let's zoom in on `xfs_defer_pending_cancel_work` and `xfs_defer_finish_noroll`. The names themselves give me some clues. `cancel_work` implies that this is where we're dealing with the *removal* of a previously scheduled deferred operation, probably due to some kind of conflict or early completion. I bet this is where the logic to prevent double-execution, or handling of partially completed operations, sits.
`finish_noroll`, however, is immediately more interesting to me. "No roll" suggests this is where we are finalizing an operation with no changes persisted to the log, which points to this function possibly being a safety check or a means of cleanup for transactions which didn't need to commit. I would expect this part of the code to handle freeing resources associated with an operation which wasn't fully processed or was made redundant. In an XFS context, I'm thinking metadata buffers and the state of the transaction within the deferral context are the core elements here.
I'm betting these functions are heavily intertwined ā `cancel_work` likely *calls* `finish_noroll` as part of the cancellation process, or they coordinate through flags and states to ensure that nothing gets missed when a deferred operation is interrupted. To understand this properly, I need to see how they interact with the overall deferral mechanism and how state is preserved and restored. I want to see how this fits in with other deferral related work and its relationship to the XFS transaction management in general. I have to think about what data structures are being modified, how the logging and journaling fit into this picture, and potential race conditions in this context.
|
| 24/2 |
2026/07/31 02:42 |
tool |
read-file |
0m
Args: map[File:fs/xfs/libxfs/xfs_defer.c FirstLine:700 LineCount:40]
Results: map[Contents: 700: }
701: }
702:
703: dfp = list_first_entry_or_null(&dop_pending,
704: struct xfs_defer_pending, dfp_list);
705: if (!dfp)
706: break;
707: error = xfs_defer_finish_one(*tp, dfp);
708: if (error && error != -EAGAIN)
709: goto out_shutdown;
710: }
711:
712: /* Requeue the paused items in the outgoing transaction. */
713: list_splice_tail_init(&dop_paused, &(*tp)->t_dfops);
714:
715: trace_xfs_defer_finish_done(*tp, _RET_IP_);
716: return 0;
717:
718: out_shutdown:
719: list_splice_tail_init(&dop_paused, &dop_pending);
720: xfs_defer_trans_abort(*tp, &dop_pending);
721: xfs_force_shutdown((*tp)->t_mountp, SHUTDOWN_CORRUPT_INCORE);
722: trace_xfs_defer_finish_error(*tp, error);
723: xfs_defer_cancel_list((*tp)->t_mountp, &dop_pending);
724: xfs_defer_cancel(*tp);
725: return error;
726: }
727:
728: int
729: xfs_defer_finish(
730: struct xfs_trans **tp)
731: {
732: #ifdef DEBUG
733: struct xfs_defer_pending *dfp;
734: #endif
735: int error;
736:
737: /*
738: * Finish and roll the transaction once more to avoid returning to the
739: * caller with a dirty transaction.
]
|
| 25/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 20106
output: 40
thoughts: 612
Thoughts: **XFS Deferral Mechanism: A Potential Use-After-Free Vulnerability**
Okay, so I'm digging into this XFS code, specifically around deferred operations and allocation reaping. It's becoming clear we have a potential use-after-free issue. Let me break it down.
Essentially, it looks like within `xfs_defer_finish_noroll`, if something goes wrong, like `xfs_defer_finish_one` returning an error, we jump to `out_shutdown`. At `out_shutdown`, a list named `dop_paused`, which contains deferred items, is spliced back into `dop_pending`. Critically, our deferred item (`aarp->dfp`) gets placed into this `dop_paused` list. Then, `xfs_defer_cancel_list` is called on `dop_pending`. This function then proceeds to *free* all the items in `dop_pending`, which includes our `aarp->dfp`.
Here's the problem: Later, we have `xrep_newbt_free` that iterates over a `resv_list`. Inside that loop, we call `xfs_alloc_commit_autoreap`, and in `xfs_alloc_commit_autoreap`, we're still referencing `resv->autoreap.dfp` which we thought was safe, but which was, in fact, freed inside the `xfs_defer_cancel_list` call. If `xrep_defer_finish` previously failed, the code branches to `junkit:`, and this loop executes.
Therefore, `xfs_alloc_commit_autoreap` is accessing a freed `aarp->dfp` through `resv->autoreap.dfp`, leading to a classic use-after-free vulnerability!
I need to confirm this by going back and reviewing how `resv` and `autoreap` are initialized, but the flow strongly suggests this is the case. I need to look at `fs/xfs/scrub/newbt.c` around line 209 to be certain. This is definitely something to flag.
|
| 26/2 |
2026/07/31 02:42 |
tool |
read-file |
0m
Args: map[File:fs/xfs/scrub/newbt.c FirstLine:180 LineCount:40]
Results: map[Contents: 180: }
181:
182: /*
183: * Designate specific blocks to be used to build our new btree. @pag must be
184: * a passive reference.
185: */
186: STATIC int
187: xrep_newbt_add_blocks(
188: struct xrep_newbt *xnr,
189: struct xfs_perag *pag,
190: const struct xfs_alloc_arg *args)
191: {
192: struct xfs_mount *mp = xnr->sc->mp;
193: struct xrep_newbt_resv *resv;
194: int error;
195:
196: resv = kmalloc_obj(struct xrep_newbt_resv, XCHK_GFP_FLAGS);
197: if (!resv)
198: return -ENOMEM;
199:
200: INIT_LIST_HEAD(&resv->list);
201: resv->agbno = XFS_FSB_TO_AGBNO(mp, args->fsbno);
202: resv->len = args->len;
203: resv->used = 0;
204: resv->pag = xfs_perag_hold(pag);
205:
206: if (args->tp) {
207: ASSERT(xnr->oinfo.oi_offset == 0);
208:
209: error = xfs_alloc_schedule_autoreap(args,
210: XFS_FREE_EXTENT_SKIP_DISCARD, &resv->autoreap);
211: if (error)
212: goto out_pag;
213: }
214:
215: list_add_tail(&resv->list, &xnr->resv_list);
216: return 0;
217: out_pag:
218: xfs_perag_put(resv->pag);
219: kfree(resv);
]
|
| 27/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 21837
output: 26
thoughts: 45
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Analyzing the Clarity and Structure**
Wow, this is exceptionally well-defined and straightforward. I immediately appreciate the clarity. Now, my mind is already jumping to the details. I need to dive into the specifics of the `struct xrep_newbt_resv` structure. I'll need to figure out its layout and composition. Let's see... I'll pull up `codesearch-struct-layout` or possibly the direct source definition using `codesearch-definition-source`. That should give me a solid handle on how it's actually built, and how the memory is laid out. I have to look into the fields.
|
| 28/2 |
2026/07/31 02:42 |
tool |
codesearch-struct-layout |
0m
Args: map[Name:xrep_newbt_resv]
Results: map[Fields:[map[Name:list OffsetBits:0 SizeBits:128] map[Name:pag OffsetBits:128 SizeBits:64] map[Name:autoreap OffsetBits:192 SizeBits:64] map[Name:agbno OffsetBits:256 SizeBits:32] map[Name:len OffsetBits:288 SizeBits:32] map[Name:used OffsetBits:320 SizeBits:32]]]
|
| 29/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 22191
output: 25
thoughts: 31
Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue:
**Diving into the `autoreap` Structure**
Alright, so `autoreap` is of type `struct xfs_alloc_autoreap`, got it. Now, what's inside that `struct`? Let's quickly pull up the definition of `xfs_alloc_autoreap`. I need to understand its members, their purpose, and how they relate to the autoreap process within XFS allocation. Is it holding things related to space accounting? Maybe it tracks some kind of reclaim state, or maybe keeps track of inode blocks. Depending on the members, this struct will indicate if we can expect certain behaviours or possible memory-related operations. I expect this structure to shed light on how the filesystem manages automatically reaping, so I can better understand its performance implications.
|
| 30/2 |
2026/07/31 02:42 |
tool |
codesearch-struct-layout |
0m
Args: map[Name:xfs_alloc_autoreap]
Results: map[Fields:[map[Name:dfp OffsetBits:0 SizeBits:64]]]
|
| 31/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 22461
output: 35
thoughts: 887
Thoughts: **Analyzing the Allocation and Freeing Sequence**
Okay, so I've got this `struct xfs_alloc_autoreap` that just contains a `struct xfs_defer_pending *dfp`. `resv->autoreap.dfp` is definitely pointing to this defer pending structure. Let's see what's happening in this rmapbt repair sequence.
First, `xrep_rmap_build_new_tree` kicks things off. It calls `xrep_rmap_reserve_space`, which goes through `xrep_rmap_try_reserve` and then into `xrep_newbt_alloc_ag_blocks`. Within `xrep_newbt_alloc_ag_blocks`, blocks get allocated, and `xrep_newbt_add_blocks` is invoked.
Here's where it gets interesting: `xrep_newbt_add_blocks` allocates a `struct xrep_newbt_resv` and then calls `xfs_alloc_schedule_autoreap`. This is a critical step, as `xfs_alloc_schedule_autoreap` calls `xfs_defer_extent_free`, which allocates the `struct xfs_defer_pending` ā the very structure that's central to this bug! The pointer to this `xfs_defer_pending` is carefully saved in `resv->autoreap.dfp`.
Immediately after, `xfs_alloc_schedule_autoreap` calls `xfs_defer_item_pause`, and the `dfp` is marked as paused. Then, back in `xrep_newbt_alloc_ag_blocks`, `xrep_defer_finish(sc)` is called. This chains to `xfs_defer_finish` and then `xfs_defer_finish_noroll`. It looks like some error pops up (or maybe a transaction abort/shutdown), and it jumps to `out_shutdown:`.
Crucially, in `out_shutdown:`, it splices `dop_paused` (which *has* the paused `dfp`) back to `dop_pending`. Then `xfs_defer_cancel_list` is called, which *frees* all pending items in `dop_pending`, including our `dfp`! That's the free stack in the bug.
The error is then returned back up the call chain to `xrep_rmap_build_new_tree`. Because of the error, `xrep_newbt_free` is called to clean up. In `xrep_newbt_free`, the code iterates through `xnr->resv_list` and calls `xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap)`. This is where the problem is realized.
Inside `xfs_alloc_commit_autoreap`, it checks if `aarp->dfp` is not NULL and, if so, it calls `xfs_defer_item_unpause(tp, aarp->dfp)`. Here's where it goes south ā `xfs_defer_item_unpause` tries to access `dfp->dfp_flags` (which is 60 bytes into the object that was already freed!). BAM! KASAN catches the slab-use-after-free.
This is a fantastic report ā a tight and actionable chain! Now, I need to check the history. Let me use `git log` to see if there are any other places where `aarp->dfp` is cleared or if there's a known fix or a related commit around `xfs_alloc_commit_autoreap` or `xrep_newbt_free`. Let's see if we can find some clues in there.
|
| 32/2 |
2026/07/31 02:42 |
tool |
git-log |
0m
Args: map[PathPrefix:fs/xfs/scrub/newbt.c Since:3 years]
Results: map[Output:ee237a900cee xfs: add a xfs_rmap_inode_bmbt_owner
f8b7c9a8b0a9 xfs: add a XFS_INO_TO_FSB helper
69050f8d6d07 treewide: Replace kmalloc with kmalloc_obj for non-scalar types
cf9b52fa7d65 xfs: directly include xfs_platform.h
d5b157e088c9 xfs: remove static reap limits from repair.h
712bae966318 xfs: generalize the freespace and reserved blocks handling
c6904f6788b7 xfs: support repairing metadata btrees rooted in metadir inodes
e9c4d8bfb26c xfs: factor out a generic xfs_group structure
dc8df7e3826e xfs: pass the pag to the xrep_newbt_extent_class tracepoints
856a920ac2bb xfs: add xfs_agbno_to_fsb and xfs_agbno_to_daddr helpers
]
|
| 33/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 24486
output: 25
thoughts: 33
Thoughts: Okay, let's dive into this.
**Examining Commit 712bae966318: A Deep Dive**
Right, so I want to get a good look at this particular commit, `712bae966318`. I know from experience that just skimming the commit message might not be enough to truly understand the impact of the changes. I need the full picture, and that means I need to see *exactly* what files were modified, and specifically *how* they were modified. I'm going to leverage `git-show` here. That will provide a clear, detailed diff. It will lay out the precise lines added, removed, or changed. This is the foundation I need for any proper analysis. Let's see what this commit has in store!
|
| 34/2 |
2026/07/31 02:42 |
tool |
git-show |
0m
Args:
Results: map[Output:commit 712bae96631852c1a1822ee4f57a08ccd843358b
Author: Christoph Hellwig <hch@lst.de>
Date: Sun Feb 9 05:43:50 2025 +0100
xfs: generalize the freespace and reserved blocks handling
xfs_{add,dec}_freecounter already handles the block and RT extent
percpu counters, but it currently hardcodes the passed in counter.
Add a freecounter abstraction that uses an enum to designate the counter
and add wrappers that hide the actual percpu_counters. This will allow
expanding the reserved block handling to the RT extent counter in the
next step, and also prepares for adding yet another such counter that
can share the code. Both these additions will be needed for the zoned
allocator.
Also switch the flooring of the frextents counter to 0 in statfs for the
rthinherit case to a manual min_t call to match the handling of the
fdblocks counter for normal file systems.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
index f3a840a425f5..57513ba19d6a 100644
--- a/fs/xfs/libxfs/xfs_ialloc.c
+++ b/fs/xfs/libxfs/xfs_ialloc.c
@@ -1927,7 +1927,7 @@ xfs_dialloc(
* that we can immediately allocate, but then we allow allocation on the
* second pass if we fail to find an AG with free inodes in it.
*/
- if (percpu_counter_read_positive(&mp->m_fdblocks) <
+ if (xfs_estimate_freecounter(mp, XC_FREE_BLOCKS) <
mp->m_low_space[XFS_LOWSP_1_PCNT]) {
ok_alloc = false;
low_space = true;
diff --git a/fs/xfs/libxfs/xfs_metafile.c b/fs/xfs/libxfs/xfs_metafile.c
index 2f5f554a36d4..7625e694eb8d 100644
--- a/fs/xfs/libxfs/xfs_metafile.c
+++ b/fs/xfs/libxfs/xfs_metafile.c
@@ -95,7 +95,7 @@ xfs_metafile_resv_can_cover(
* There aren't enough blocks left in the inode's reservation, but it
* isn't critical unless there also isn't enough free space.
*/
- return __percpu_counter_compare(&ip->i_mount->m_fdblocks,
+ return xfs_compare_freecounter(ip->i_mount, XC_FREE_BLOCKS,
rhs - ip->i_delayed_blks, 2048) >= 0;
}
diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
index 3dc5f5dba162..3fdd20df961c 100644
--- a/fs/xfs/libxfs/xfs_sb.c
+++ b/fs/xfs/libxfs/xfs_sb.c
@@ -1265,8 +1265,7 @@ xfs_log_sb(
mp->m_sb.sb_ifree = min_t(uint64_t,
percpu_counter_sum_positive(&mp->m_ifree),
mp->m_sb.sb_icount);
- mp->m_sb.sb_fdblocks =
- percpu_counter_sum_positive(&mp->m_fdblocks);
+ mp->m_sb.sb_fdblocks = xfs_sum_freecounter(mp, XC_FREE_BLOCKS);
}
/*
@@ -1275,9 +1274,10 @@ xfs_log_sb(
* we handle nearly-lockless reservations, so we must use the _positive
* variant here to avoid writing out nonsense frextents.
*/
- if (xfs_has_rtgroups(mp))
+ if (xfs_has_rtgroups(mp)) {
mp->m_sb.sb_frextents =
- percpu_counter_sum_positive(&mp->m_frextents);
+ xfs_sum_freecounter(mp, XC_FREE_RTEXTENTS);
+ }
xfs_sb_to_disk(bp->b_addr, &mp->m_sb);
xfs_trans_buf_set_type(tp, bp, XFS_BLFT_SB_BUF);
diff --git a/fs/xfs/libxfs/xfs_types.h b/fs/xfs/libxfs/xfs_types.h
index ca2401c1facd..76f3c31573ec 100644
--- a/fs/xfs/libxfs/xfs_types.h
+++ b/fs/xfs/libxfs/xfs_types.h
@@ -233,6 +233,23 @@ enum xfs_group_type {
{ XG_TYPE_AG, "ag" }, \
{ XG_TYPE_RTG, "rtg" }
+enum xfs_free_counter {
+ /*
+ * Number of free blocks on the data device.
+ */
+ XC_FREE_BLOCKS,
+
+ /*
+ * Number of free RT extents on the RT device.
+ */
+ XC_FREE_RTEXTENTS,
+ XC_FREE_NR,
+};
+
+#define XFS_FREECOUNTER_STR \
+ { XC_FREE_BLOCKS, "blocks" }, \
+ { XC_FREE_RTEXTENTS, "rtextents" }
+
/*
* Type verifier functions
*/
diff --git a/fs/xfs/scrub/fscounters.c b/fs/xfs/scrub/fscounters.c
index ca23cf4db6c5..207a238de429 100644
--- a/fs/xfs/scrub/fscounters.c
+++ b/fs/xfs/scrub/fscounters.c
@@ -513,8 +513,8 @@ xchk_fscounters(
/* Snapshot the percpu counters. */
icount = percpu_counter_sum(&mp->m_icount);
ifree = percpu_counter_sum(&mp->m_ifree);
- fdblocks = percpu_counter_sum(&mp->m_fdblocks);
- frextents = percpu_counter_sum(&mp->m_frextents);
+ fdblocks = xfs_sum_freecounter_raw(mp, XC_FREE_BLOCKS);
+ frextents = xfs_sum_freecounter_raw(mp, XC_FREE_RTEXTENTS);
/* No negative values, please! */
if (icount < 0 || ifree < 0)
@@ -589,15 +589,16 @@ xchk_fscounters(
try_again = true;
}
- if (!xchk_fscount_within_range(sc, fdblocks, &mp->m_fdblocks,
- fsc->fdblocks)) {
+ if (!xchk_fscount_within_range(sc, fdblocks,
+ &mp->m_free[XC_FREE_BLOCKS].count, fsc->fdblocks)) {
if (fsc->frozen)
xchk_set_corrupt(sc);
else
try_again = true;
}
- if (!xchk_fscount_within_range(sc, frextents, &mp->m_frextents,
+ if (!xchk_fscount_within_range(sc, frextents,
+ &mp->m_free[XC_FREE_RTEXTENTS].count,
fsc->frextents - fsc->frextents_delayed)) {
if (fsc->frozen)
xchk_set_corrupt(sc);
diff --git a/fs/xfs/scrub/fscounters_repair.c b/fs/xfs/scrub/fscounters_repair.c
index cda13447a373..8fb0db78489e 100644
--- a/fs/xfs/scrub/fscounters_repair.c
+++ b/fs/xfs/scrub/fscounters_repair.c
@@ -64,7 +64,7 @@ xrep_fscounters(
percpu_counter_set(&mp->m_icount, fsc->icount);
percpu_counter_set(&mp->m_ifree, fsc->ifree);
- percpu_counter_set(&mp->m_fdblocks, fsc->fdblocks);
+ xfs_set_freecounter(mp, XC_FREE_BLOCKS, fsc->fdblocks);
/*
* Online repair is only supported on v5 file systems, which require
@@ -74,7 +74,7 @@ xrep_fscounters(
* track of the delalloc reservations separately, as they are are
* subtracted from m_frextents, but not included in sb_frextents.
*/
- percpu_counter_set(&mp->m_frextents,
+ xfs_set_freecounter(mp, XC_FREE_RTEXTENTS,
fsc->frextents - fsc->frextents_delayed);
if (!xfs_has_rtgroups(mp))
mp->m_sb.sb_frextents = fsc->frextents;
diff --git a/fs/xfs/scrub/newbt.c b/fs/xfs/scrub/newbt.c
index ac38f5843090..1588ce971cb8 100644
--- a/fs/xfs/scrub/newbt.c
+++ b/fs/xfs/scrub/newbt.c
@@ -62,7 +62,7 @@ xrep_newbt_estimate_slack(
free = sc->sa.pag->pagf_freeblks;
sz = xfs_ag_block_count(sc->mp, pag_agno(sc->sa.pag));
} else {
- free = percpu_counter_sum(&sc->mp->m_fdblocks);
+ free = xfs_sum_freecounter_raw(sc->mp, XC_FREE_BLOCKS);
sz = sc->mp->m_sb.sb_dblocks;
}
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 455298503d01..58249f37a7ad 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -409,7 +409,7 @@ xfs_reserve_blocks(
/*
* If the request is larger than the current reservation, reserve the
- * blocks before we update the reserve counters. Sample m_fdblocks and
+ * blocks before we update the reserve counters. Sample m_free and
* perform a partial reservation if the request exceeds free space.
*
* The code below estimates how many blocks it can request from
@@ -419,8 +419,8 @@ xfs_reserve_blocks(
* space to fill it because mod_fdblocks will refill an undersized
* reserve when it can.
*/
- free = percpu_counter_sum(&mp->m_fdblocks) -
- xfs_fdblocks_unavailable(mp);
+ free = xfs_sum_freecounter_raw(mp, XC_FREE_BLOCKS) -
+ xfs_freecounter_unavailable(mp, XC_FREE_BLOCKS);
delta = request - mp->m_resblks;
mp->m_resblks = request;
if (delta > 0 && free > 0) {
diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index 7b6c026d01a1..c9ded501e89b 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -2076,7 +2076,7 @@ xfs_inodegc_want_queue_rt_file(
if (!XFS_IS_REALTIME_INODE(ip))
return false;
- if (__percpu_counter_compare(&mp->m_frextents,
+ if (xfs_compare_freecounter(mp, XC_FREE_RTEXTENTS,
mp->m_low_rtexts[XFS_LOWSP_5_PCNT],
XFS_FDBLOCKS_BATCH) < 0)
return true;
@@ -2104,7 +2104,7 @@ xfs_inodegc_want_queue_work(
if (items > mp->m_ino_geo.inodes_per_cluster)
return true;
- if (__percpu_counter_compare(&mp->m_fdblocks,
+ if (xfs_compare_freecounter(mp, XC_FREE_BLOCKS,
mp->m_low_space[XFS_LOWSP_5_PCNT],
XFS_FDBLOCKS_BATCH) < 0)
return true;
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index ed85322507dd..0418aad2db91 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1155,9 +1155,9 @@ xfs_ioctl_fs_counts(
struct xfs_fsop_counts out = {
.allocino = percpu_counter_read_positive(&mp->m_icount),
.freeino = percpu_counter_read_positive(&mp->m_ifree),
- .freedata = percpu_counter_read_positive(&mp->m_fdblocks) -
- xfs_fdblocks_unavailable(mp),
- .freertx = percpu_counter_read_positive(&mp->m_frextents),
+ .freedata = xfs_estimate_freecounter(mp, XC_FREE_BLOCKS) -
+ xfs_freecounter_unavailable(mp, XC_FREE_BLOCKS),
+ .freertx = xfs_estimate_freecounter(mp, XC_FREE_RTEXTENTS),
};
if (copy_to_user(uarg, &out, sizeof(out)))
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 46acf727cbe7..c669b93bb2d1 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -431,13 +431,14 @@ xfs_quota_calc_throttle(
static int64_t
xfs_iomap_freesp(
- struct percpu_counter *counter,
+ struct xfs_mount *mp,
+ unsigned int idx,
uint64_t low_space[XFS_LOWSP_MAX],
int *shift)
{
int64_t freesp;
- freesp = percpu_counter_read_positive(counter);
+ freesp = xfs_estimate_freecounter(mp, idx);
if (freesp < low_space[XFS_LOWSP_5_PCNT]) {
*shift = 2;
if (freesp < low_space[XFS_LOWSP_4_PCNT])
@@ -536,10 +537,10 @@ xfs_iomap_prealloc_size(
if (unlikely(XFS_IS_REALTIME_INODE(ip)))
freesp = xfs_rtbxlen_to_blen(mp,
- xfs_iomap_freesp(&mp->m_frextents,
+ xfs_iomap_freesp(mp, XC_FREE_RTEXTENTS,
mp->m_low_rtexts, &shift));
else
- freesp = xfs_iomap_freesp(&mp->m_fdblocks, mp->m_low_space,
+ freesp = xfs_iomap_freesp(mp, XC_FREE_BLOCKS, mp->m_low_space,
&shift);
/*
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index ba6e60dc3a45..f444b41d4587 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1220,13 +1220,31 @@ xfs_fs_writable(
return true;
}
+/*
+ * Estimate the amount of free space that is not available to userspace and is
+ * not explicitly reserved from the incore fdblocks. This includes:
+ *
+ * - The minimum number of blocks needed to support splitting a bmap btree
+ * - The blocks currently in use by the freespace btrees because they record
+ * the actual blocks that will fill per-AG metadata space reservations
+ */
+uint64_t
+xfs_freecounter_unavailable(
+ struct xfs_mount *mp,
+ enum xfs_free_counter ctr)
+{
+ if (ctr != XC_FREE_BLOCKS)
+ return 0;
+ return mp->m_alloc_set_aside + atomic64_read(&mp->m_allocbt_blks);
+}
+
void
xfs_add_freecounter(
struct xfs_mount *mp,
- struct percpu_counter *counter,
+ enum xfs_free_counter ctr,
uint64_t delta)
{
- bool has_resv_pool = (counter == &mp->m_fdblocks);
+ bool has_resv_pool = (ctr == XC_FREE_BLOCKS);
uint64_t res_used;
/*
@@ -1234,7 +1252,7 @@ xfs_add_freecounter(
* Most of the time the pool is full.
*/
if (!has_resv_pool || mp->m_resblks == mp->m_resblks_avail) {
- percpu_counter_add(counter, delta);
+ percpu_counter_add(&mp->m_free[ctr].count, delta);
return;
}
@@ -1245,24 +1263,27 @@ xfs_add_freecounter(
} else {
delta -= res_used;
mp->m_resblks_avail = mp->m_resblks;
- percpu_counter_add(counter, delta);
+ percpu_counter_add(&mp->m_free[ctr].count, delta);
}
spin_unlock(&mp->m_sb_lock);
}
+
+/* Adjust in-core free blocks or RT extents. */
int
xfs_dec_freecounter(
struct xfs_mount *mp,
- struct percpu_counter *counter,
+ enum xfs_free_counter ctr,
uint64_t delta,
bool rsvd)
{
+ struct percpu_counter *counter = &mp->m_free[ctr].count;
uint64_t set_aside = 0;
s32 batch;
bool has_resv_pool;
- ASSERT(counter == &mp->m_fdblocks || counter == &mp->m_frextents);
- has_resv_pool = (counter == &mp->m_fdblocks);
+ ASSERT(ctr < XC_FREE_NR);
+ has_resv_pool = (ctr == XC_FREE_BLOCKS);
if (rsvd)
ASSERT(has_resv_pool);
@@ -1292,7 +1313,7 @@ xfs_dec_freecounter(
* slightly premature -ENOSPC.
*/
if (has_resv_pool)
- set_aside = xfs_fdblocks_unavailable(mp);
+ set_aside = xfs_freecounter_unavailable(mp, ctr);
percpu_counter_add_batch(counter, -((int64_t)delta), batch);
if (__percpu_counter_compare(counter, set_aside,
XFS_FDBLOCKS_BATCH) < 0) {
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index fbed172d6770..7f3265d669bc 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -105,6 +105,11 @@ struct xfs_groups {
uint64_t blkmask;
};
+struct xfs_freecounter {
+ /* free blocks for general use: */
+ struct percpu_counter count;
+};
+
/*
* The struct xfsmount layout is optimised to separate read-mostly variables
* from variables that are frequently modified. We put the read-mostly variables
@@ -222,8 +227,8 @@ typedef struct xfs_mount {
spinlock_t ____cacheline_aligned m_sb_lock; /* sb counter lock */
struct percpu_counter m_icount; /* allocated inodes counter */
struct percpu_counter m_ifree; /* free inodes counter */
- struct percpu_counter m_fdblocks; /* free block counter */
- struct percpu_counter m_frextents; /* free rt extent counter */
+
+ struct xfs_freecounter m_free[XC_FREE_NR];
/*
* Count of data device blocks reserved for delayed allocations,
@@ -646,45 +651,74 @@ extern void xfs_unmountfs(xfs_mount_t *);
*/
#define XFS_FDBLOCKS_BATCH 1024
+uint64_t xfs_freecounter_unavailable(struct xfs_mount *mp,
+ enum xfs_free_counter ctr);
+
/*
- * Estimate the amount of free space that is not available to userspace and is
- * not explicitly reserved from the incore fdblocks. This includes:
- *
- * - The minimum number of blocks needed to support splitting a bmap btree
- * - The blocks currently in use by the freespace btrees because they record
- * the actual blocks that will fill per-AG metadata space reservations
+ * Sum up the freecount, but never return negative values.
*/
-static inline uint64_t
-xfs_fdblocks_unavailable(
- struct xfs_mount *mp)
+static inline s64 xfs_sum_freecounter(struct xfs_mount *mp,
+ enum xfs_free_counter ctr)
+{
+ return percpu_counter_sum_positive(&mp->m_free[ctr].count);
+}
+
+/*
+ * Same as above, but does return negative values. Mostly useful for
+ * special cases like repair and tracing.
+ */
+static inline s64 xfs_sum_freecounter_raw(struct xfs_mount *mp,
+ enum xfs_free_counter ctr)
+{
+ return percpu_counter_sum(&mp->m_free[ctr].count);
+}
+
+/*
+ * This just provides and estimate without the cpu-local updates, use
+ * xfs_sum_freecounter for the exact value.
+ */
+static inline s64 xfs_estimate_freecounter(struct xfs_mount *mp,
+ enum xfs_free_counter ctr)
+{
+ return percpu_counter_read_positive(&mp->m_free[ctr].count);
+}
+
+static inline int xfs_compare_freecounter(struct xfs_mount *mp,
+ enum xfs_free_counter ctr, s64 rhs, s32 batch)
+{
+ return __percpu_counter_compare(&mp->m_free[ctr].count, rhs, batch);
+}
+
+static inline void xfs_set_freecounter(struct xfs_mount *mp,
+ enum xfs_free_counter ctr, uint64_t val)
{
- return mp->m_alloc_set_aside + atomic64_read(&mp->m_allocbt_blks);
+ percpu_counter_set(&mp->m_free[ctr].count, val);
}
-int xfs_dec_freecounter(struct xfs_mount *mp, struct percpu_counter *counter,
+int xfs_dec_freecounter(struct xfs_mount *mp, enum xfs_free_counter ctr,
uint64_t delta, bool rsvd);
-void xfs_add_freecounter(struct xfs_mount *mp, struct percpu_counter *counter,
+void xfs_add_freecounter(struct xfs_mount *mp, enum xfs_free_counter ctr,
uint64_t delta);
static inline int xfs_dec_fdblocks(struct xfs_mount *mp, uint64_t delta,
bool reserved)
{
- return xfs_dec_freecounter(mp, &mp->m_fdblocks, delta, reserved);
+ return xfs_dec_freecounter(mp, XC_FREE_BLOCKS, delta, reserved);
}
static inline void xfs_add_fdblocks(struct xfs_mount *mp, uint64_t delta)
{
- xfs_add_freecounter(mp, &mp->m_fdblocks, delta);
+ xfs_add_freecounter(mp, XC_FREE_BLOCKS, delta);
}
static inline int xfs_dec_frextents(struct xfs_mount *mp, uint64_t delta)
{
- return xfs_dec_freecounter(mp, &mp->m_frextents, delta, false);
+ return xfs_dec_freecounter(mp, XC_FREE_RTEXTENTS, delta, false);
}
static inline void xfs_add_frextents(struct xfs_mount *mp, uint64_t delta)
{
- xfs_add_freecounter(mp, &mp->m_frextents, delta);
+ xfs_add_freecounter(mp, XC_FREE_RTEXTENTS, delta);
}
extern int xfs_readsb(xfs_mount_t *, int);
diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
index 57bef567e011..93caf4406402 100644
--- a/fs/xfs/xfs_rtalloc.c
+++ b/fs/xfs/xfs_rtalloc.c
@@ -1519,7 +1519,7 @@ xfs_rtalloc_reinit_frextents(
spin_lock(&mp->m_sb_lock);
mp->m_sb.sb_frextents = val;
spin_unlock(&mp->m_sb_lock);
- percpu_counter_set(&mp->m_frextents, mp->m_sb.sb_frextents);
+ xfs_set_freecounter(mp, XC_FREE_RTEXTENTS, mp->m_sb.sb_frextents);
return 0;
}
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 0055066fb1d9..b08d28a895cb 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -834,10 +834,12 @@ xfs_statfs_data(
struct kstatfs *st)
{
int64_t fdblocks =
- percpu_counter_sum(&mp->m_fdblocks);
+ xfs_sum_freecounter(mp, XC_FREE_BLOCKS);
/* make sure st->f_bfree does not underflow */
- st->f_bfree = max(0LL, fdblocks - xfs_fdblocks_unavailable(mp));
+ st->f_bfree = max(0LL,
+ fdblocks - xfs_freecounter_unavailable(mp, XC_FREE_BLOCKS));
+
/*
* sb_dblocks can change during growfs, but nothing cares about reporting
* the old or new value during growfs.
@@ -856,7 +858,7 @@ xfs_statfs_rt(
struct kstatfs *st)
{
st->f_bfree = xfs_rtbxlen_to_blen(mp,
- percpu_counter_sum_positive(&mp->m_frextents));
+ xfs_sum_freecounter(mp, XC_FREE_RTEXTENTS));
st->f_blocks = mp->m_sb.sb_rblocks;
}
@@ -1065,7 +1067,8 @@ static int
xfs_init_percpu_counters(
struct xfs_mount *mp)
{
- int error;
+ int error;
+ int i;
error = percpu_counter_init(&mp->m_icount, 0, GFP_KERNEL);
if (error)
@@ -1075,30 +1078,29 @@ xfs_init_percpu_counters(
if (error)
goto free_icount;
- error = percpu_counter_init(&mp->m_fdblocks, 0, GFP_KERNEL);
- if (error)
- goto free_ifree;
-
error = percpu_counter_init(&mp->m_delalloc_blks, 0, GFP_KERNEL);
if (error)
- goto free_fdblocks;
+ goto free_ifree;
error = percpu_counter_init(&mp->m_delalloc_rtextents, 0, GFP_KERNEL);
if (error)
goto free_delalloc;
- error = percpu_counter_init(&mp->m_frextents, 0, GFP_KERNEL);
- if (error)
- goto free_delalloc_rt;
+ for (i = 0; i < XC_FREE_NR; i++) {
+ error = percpu_counter_init(&mp->m_free[i].count, 0,
+ GFP_KERNEL);
+ if (error)
+ goto free_freecounters;
+ }
return 0;
-free_delalloc_rt:
+free_freecounters:
+ while (--i > 0)
+ percpu_counter_destroy(&mp->m_free[i].count);
percpu_counter_destroy(&mp->m_delalloc_rtextents);
free_delalloc:
percpu_counter_destroy(&mp->m_delalloc_blks);
-free_fdblocks:
- percpu_counter_destroy(&mp->m_fdblocks);
free_ifree:
percpu_counter_destroy(&mp->m_ifree);
free_icount:
@@ -1112,24 +1114,26 @@ xfs_reinit_percpu_counters(
{
percpu_counter_set(&mp->m_icount, mp->m_sb.sb_icount);
percpu_counter_set(&mp->m_ifree, mp->m_sb.sb_ifree);
- percpu_counter_set(&mp->m_fdblocks, mp->m_sb.sb_fdblocks);
- percpu_counter_set(&mp->m_frextents, mp->m_sb.sb_frextents);
+ xfs_set_freecounter(mp, XC_FREE_BLOCKS, mp->m_sb.sb_fdblocks);
+ xfs_set_freecounter(mp, XC_FREE_RTEXTENTS, mp->m_sb.sb_frextents);
}
static void
xfs_destroy_percpu_counters(
struct xfs_mount *mp)
{
+ enum xfs_free_counter i;
+
+ for (i = 0; i < XC_FREE_NR; i++)
+ percpu_counter_destroy(&mp->m_free[i].count);
percpu_counter_destroy(&mp->m_icount);
percpu_counter_destroy(&mp->m_ifree);
- percpu_counter_destroy(&mp->m_fdblocks);
ASSERT(xfs_is_shutdown(mp) ||
percpu_counter_sum(&mp->m_delalloc_rtextents) == 0);
percpu_counter_destroy(&mp->m_delalloc_rtextents);
ASSERT(xfs_is_shutdown(mp) ||
percpu_counter_sum(&mp->m_delalloc_blks) == 0);
percpu_counter_destroy(&mp->m_delalloc_blks);
- percpu_counter_destroy(&mp->m_frextents);
}
static int
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index bfc2f1249022..f97129f01b48 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -5622,7 +5622,7 @@ DECLARE_EVENT_CLASS(xfs_metafile_resv_class,
__entry->dev = mp->m_super->s_dev;
__entry->ino = ip->i_ino;
- __entry->freeblks = percpu_counter_sum(&mp->m_fdblocks);
+ __entry->freeblks = xfs_sum_freecounter_raw(mp, XC_FREE_BLOCKS);
__entry->reserved = ip->i_delayed_blks;
__entry->asked = ip->i_meta_resv_asked;
__entry->used = ip->i_nblocks;
]
|
| 35/2 |
2026/07/31 02:42 |
llm |
expert |
0m
Model:
Tokens:
input: 33838
output: 33
thoughts: 49
Thoughts: **Debugging Thoughts**
Okay, so this commit isn't the culprit for the bug I'm chasing. Time to dig deeper. I need to understand the history of these allocation autoreap functions. I'll search the git history for the introduction of `xfs_alloc_commit_autoreap` and `xfs_alloc_schedule_autoreap`. Knowing *when* they were introduced will help me narrow down the possible changes that might have caused the issue. This feels like a good starting point to trace the problem. Let's see what the git logs reveal.
|
| 36/2 |
2026/07/31 02:43 |
tool |
git-log |
5m
Args: map[CodeRegexp:xfs_alloc_commit_autoreap Since:3 years]
Results: map[Output:6bb9ea8ecd2c xfs: log EFIs for all btree blocks being used to stage a btree
e3042be36c34 xfs: automatic freeing of freshly allocated unwritten space
]
|
| 37/2 |
2026/07/31 02:48 |
llm |
expert |
0m
Model:
Tokens:
input: 34103
output: 23
thoughts: 50
Thoughts: Okay, let's dive into this. Here's how I'm thinking about it:
**Analyzing Recent Commits**
Right, let's start by zeroing in on those two commits, `e3042be36c34` and `6bb9ea8ecd2c`. I'm curious to see what changed and how they relate. I want to start by examining the second commit, `6bb9ea8ecd2c`, in detail. I'll use `git-show` on that commit specifically. That should provide a clear picture of its content and any associated metadata, which is what I need to understand it fully. I'm hoping this will provide a good baseline for comparison.
|
| 38/2 |
2026/07/31 02:48 |
tool |
git-show |
0m
Args:
Results: map[Output:commit 6bb9ea8ecd2c58a66324cb799838e7d49d78a877
Author: Darrick J. Wong <djwong@kernel.org>
Date: Wed Dec 6 18:41:00 2023 -0800
xfs: log EFIs for all btree blocks being used to stage a btree
We need to log EFIs for every extent that we allocate for the purpose of
staging a new btree so that if we fail then the blocks will be freed
during log recovery. Use the autoreaping mechanism provided by the
previous patch to attach paused freeing work to the scrub transaction.
We can then mark the EFIs stale if we decide to commit the new btree, or
we can unpause the EFIs if we decide to abort the repair.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/xfs/scrub/newbt.c b/fs/xfs/scrub/newbt.c
index 5d1d75d2b1ad..992cf34a13e7 100644
--- a/fs/xfs/scrub/newbt.c
+++ b/fs/xfs/scrub/newbt.c
@@ -139,6 +139,7 @@ xrep_newbt_add_blocks(
{
struct xfs_mount *mp = xnr->sc->mp;
struct xrep_newbt_resv *resv;
+ int error;
resv = kmalloc(sizeof(struct xrep_newbt_resv), XCHK_GFP_FLAGS);
if (!resv)
@@ -150,8 +151,18 @@ xrep_newbt_add_blocks(
resv->used = 0;
resv->pag = xfs_perag_hold(pag);
+ ASSERT(xnr->oinfo.oi_offset == 0);
+
+ error = xfs_alloc_schedule_autoreap(args, true, &resv->autoreap);
+ if (error)
+ goto out_pag;
+
list_add_tail(&resv->list, &xnr->resv_list);
return 0;
+out_pag:
+ xfs_perag_put(resv->pag);
+ kfree(resv);
+ return error;
}
/* Don't let our allocation hint take us beyond this AG */
@@ -330,16 +341,21 @@ xrep_newbt_free_extent(
if (!btree_committed || resv->used == 0) {
/*
* If we're not committing a new btree or we didn't use the
- * space reservation, free the entire space extent.
+ * space reservation, let the existing EFI free the entire
+ * space extent.
*/
- goto free;
+ trace_xrep_newbt_free_blocks(sc->mp, resv->pag->pag_agno,
+ free_agbno, free_aglen, xnr->oinfo.oi_owner);
+ xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);
+ return 1;
}
/*
- * We used space and committed the btree. Remove the written blocks
- * from the reservation and possibly log a new EFI to free any unused
- * reservation space.
+ * We used space and committed the btree. Cancel the autoreap, remove
+ * the written blocks from the reservation, and possibly log a new EFI
+ * to free any unused reservation space.
*/
+ xfs_alloc_cancel_autoreap(sc->tp, &resv->autoreap);
free_agbno += resv->used;
free_aglen -= resv->used;
@@ -351,7 +367,6 @@ xrep_newbt_free_extent(
ASSERT(xnr->resv != XFS_AG_RESV_AGFL);
-free:
/*
* Use EFIs to free the reservations. This reduces the chance
* that we leak blocks if the system goes down.
@@ -411,9 +426,10 @@ xrep_newbt_free(
/*
* If we still have reservations attached to @newbt, cleanup must have
* failed and the filesystem is about to go down. Clean up the incore
- * reservations.
+ * reservations and try to commit to freeing the space we used.
*/
list_for_each_entry_safe(resv, n, &xnr->resv_list, list) {
+ xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);
list_del(&resv->list);
xfs_perag_put(resv->pag);
kfree(resv);
@@ -491,5 +507,7 @@ xrep_newbt_claim_block(
agbno));
else
ptr->s = cpu_to_be32(agbno);
- return 0;
+
+ /* Relog all the EFIs. */
+ return xrep_defer_finish(xnr->sc);
}
diff --git a/fs/xfs/scrub/newbt.h b/fs/xfs/scrub/newbt.h
index ca53271f3a4c..d2baffa17b1a 100644
--- a/fs/xfs/scrub/newbt.h
+++ b/fs/xfs/scrub/newbt.h
@@ -12,6 +12,9 @@ struct xrep_newbt_resv {
struct xfs_perag *pag;
+ /* Auto-freeing this reservation if we don't commit. */
+ struct xfs_alloc_autoreap autoreap;
+
/* AG block of the extent we reserved. */
xfs_agblock_t agbno;
]
|
| 39/2 |
2026/07/31 02:48 |
llm |
expert |
0m
Model:
Tokens:
input: 35943
output: 44
thoughts: 82
Thoughts: Okay, let's dive into this. Here's my take on those `xfs_alloc` functions:
**Analyzing XFS Autoreap Commit and Cancel**
My initial thought is to examine the behavior of `xfs_alloc_commit_autoreap` and `xfs_alloc_cancel_autoreap`. Specifically, I want to understand their roles and how they interact within the XFS allocation framework. The path `fs/xfs/libxfs/xfs_alloc.c` is the key, and Iām going to focus my attention around line 2735. This will be where I'll find the core implementation and understand their intricacies, especially how they contribute to the autoreap process. I'm keen to grasp the details of how XFS manages these resources.
|
| 40/2 |
2026/07/31 02:48 |
tool |
read-file |
0m
Args: map[File:fs/xfs/libxfs/xfs_alloc.c FirstLine:2735 LineCount:40]
Results: map[Contents:2735:
2736: /*
2737: * Cancel automatic freeing of unwritten space in the filesystem.
2738: *
2739: * Earlier, we created a paused deferred extent free item and attached it to
2740: * this transaction so that we could automatically roll back a new space
2741: * allocation if the system went down. Now we want to cancel the paused work
2742: * item by marking the EFI stale so we don't actually free the space, unpausing
2743: * the pending item and logging an EFD.
2744: *
2745: * The caller generally should have already mapped the space into the ondisk
2746: * filesystem. If the reserved space was partially used, the caller must call
2747: * xfs_free_extent_later to create a new EFI to free the unused space.
2748: */
2749: void
2750: xfs_alloc_cancel_autoreap(
2751: struct xfs_trans *tp,
2752: struct xfs_alloc_autoreap *aarp)
2753: {
2754: struct xfs_defer_pending *dfp = aarp->dfp;
2755: struct xfs_extent_free_item *xefi;
2756:
2757: if (!dfp)
2758: return;
2759:
2760: list_for_each_entry(xefi, &dfp->dfp_work, xefi_list)
2761: xefi->xefi_flags |= XFS_EFI_CANCELLED;
2762:
2763: xfs_defer_item_unpause(tp, dfp);
2764: }
2765:
2766: /*
2767: * Commit automatic freeing of unwritten space in the filesystem.
2768: *
2769: * This unpauses an earlier _schedule_autoreap and commits to freeing the
2770: * allocated space. Call this if none of the reserved space was used.
2771: */
2772: void
2773: xfs_alloc_commit_autoreap(
2774: struct xfs_trans *tp,
]
|
| 41/2 |
2026/07/31 02:48 |
llm |
expert |
0m
Model:
Tokens:
input: 36872
output: 40
thoughts: 813
Thoughts: **Analyzing Potential Dangling Pointers in XFS Deferral Mechanisms**
Okay, so I'm digging into this XFS code, and I've hit a potential issue with deferred allocation and transaction handling. It seems that if `xfs_defer_finish_noroll` fails, it calls `xfs_defer_cancel_list`, which is meant to clean up and free all the pending items in `dop_pending`. However, this is where it gets tricky. I'm concerned about how `xfs_alloc_commit_autoreap` actually knows if the `aarp->dfp` (which, I believe, refers to a deferred free pending item) has been freed.
The crux of the matter is that `aarp->dfp` might become a dangling pointer after the `xfs_defer_cancel_list` call. This is because `xfs_alloc_commit_autoreap` is called as a cleanup when the filesystem is shutting down. There's no inherent check within `xfs_alloc_commit_autoreap` to validate the pointer.
So, the key questions are: Is there a way to clear `aarp->dfp` when its corresponding `dfp` is cancelled and freed? Or, should `xfs_alloc_commit_autoreap` itself be responsible for checking if the transaction has been aborted or if the filesystem is shutting down?
This leads me to another concern. If the transaction has been aborted or the filesystem is in the process of shutting down, is it even valid to call `xfs_defer_item_unpause`? Let's quickly review the `xfs_defer_item_unpause` code block, which just unsets the pause flag. If the transaction is already dead, calling `xfs_defer_item_unpause` would be a bug.
On the other hand, during a shutdown, `xrep_newbt_free` is called, which in turn calls `xfs_alloc_commit_autoreap`. Reviewing the `xrep_newbt_free` code, it seems the code iterates a list of reservations and calls `xfs_alloc_commit_autoreap` on those items to commit and free.
Wait, if the transaction is aborted or the filesystem is shutting down, we *don't* need to unpause the deferred free pending items (`dfp`). The transaction is dead anyway, and the `dfp` has already been cancelled and freed by `xfs_defer_cancel_list`!
So, how can we detect this condition reliably? Would a check of `xfs_is_shutdown(sc->mp)` or the transaction flags (`tp->t_flags & XFS_TRANS_DIRTY` perhaps?) work, or is there another way to tell if the deferred item is still valid? Perhaps we can leverage the fact that if `xfs_defer_finish` fails, the transaction is typically aborted and the filesystem might be in the process of shutting down.
Now, let me run `codesearch-find-references` on `xfs_alloc_commit_autoreap` and `xfs_alloc_cancel_autoreap` to see where else those functions are used. Aha, just `xrep_newbt_free` and `xrep_newbt_free_extent`. So that simplifies things... I'll check `xrep_newbt_free_extent` as well. I think this points to the right area for a fix.
|
| 42/2 |
2026/07/31 02:48 |
tool |
read-file |
0m
Args: map[File:fs/xfs/scrub/newbt.c FirstLine:420 LineCount:35]
Results: map[Contents: 420: struct xrep_newbt_resv *resv,
421: bool btree_committed)
422: {
423: struct xfs_scrub *sc = xnr->sc;
424: xfs_agblock_t free_agbno = resv->agbno;
425: xfs_extlen_t free_aglen = resv->len;
426: int error;
427:
428: if (!btree_committed || resv->used == 0) {
429: /*
430: * If we're not committing a new btree or we didn't use the
431: * space reservation, let the existing EFI free the entire
432: * space extent.
433: */
434: trace_xrep_newbt_free_blocks(resv->pag, free_agbno, free_aglen,
435: xnr->oinfo.oi_owner);
436: xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);
437: return 1;
438: }
439:
440: /*
441: * We used space and committed the btree. Cancel the autoreap, remove
442: * the written blocks from the reservation, and possibly log a new EFI
443: * to free any unused reservation space.
444: */
445: xfs_alloc_cancel_autoreap(sc->tp, &resv->autoreap);
446: free_agbno += resv->used;
447: free_aglen -= resv->used;
448:
449: if (free_aglen == 0)
450: return 0;
451:
452: trace_xrep_newbt_free_blocks(resv->pag, free_agbno, free_aglen,
453: xnr->oinfo.oi_owner);
454:
]
|
| 43/2 |
2026/07/31 02:48 |
llm |
expert |
0m
Model:
Tokens:
input: 39055
output: 41
thoughts: 327
Thoughts: **Analyzing the Autoreap Function in XFS Allocation**
Okay, so I'm thinking about `xfs_alloc_commit_autoreap`. My initial question is whether this function actually needs to do anything if a transaction is aborted or the filesystem is shutting down. Intuitively, I'm thinking probably not, since a transaction that's cancelled will have all its deferred operations, including paused ones, automatically handled.
Let's quickly refresh what `xfs_alloc_commit_autoreap` *actually* does. Right, it looks like it just unpauses a deferred item if `aarp->dfp` is valid.
```c
void
xfs_alloc_commit_autoreap(
struct xfs_trans *tp,
struct xfs_alloc_autoreap *aarp)
{
if (aarp->dfp)
xfs_defer_item_unpause(tp, aarp->dfp);
}
```
So, the next thing I'm wondering is how the kernel detects if a transaction is aborted, or if the filesystem is shutting down. The transaction will have a flag set like `tp->t_flags & XFS_TRANS_DIRTY`, or perhaps the mount point's shutdown state, through `xfs_is_shutdown(tp->t_mountp)`.
I need to confirm if there is an abort flag, or if I can rely on checking the shutdown state. Time to search the `fs/xfs/libxfs/xfs_alloc.c` file for clues. I'll start with the `XFS_TRANS_` flags and then move on to `xfs_is_shutdown` within that file, to see how these situations are handled.
|
| 44/2 |
2026/07/31 02:48 |
tool |
grepper |
0m
Args: map[Expression:xfs_is_shutdown PathPrefix:fs/xfs/libxfs/xfs_alloc.c]
Results: map[Output:fs/xfs/libxfs/xfs_alloc.c=3394=xfs_alloc_read_agf(
--
fs/xfs/libxfs/xfs_alloc.c-3460- */
fs/xfs/libxfs/xfs_alloc.c:3461: if (!xfs_is_shutdown(pag_mount(pag))) {
fs/xfs/libxfs/xfs_alloc.c-3462- bool ok = true;
]
|
| 45/2 |
2026/07/31 02:48 |
llm |
expert |
0m
Model:
Tokens:
input: 39940
output: 34
thoughts: 1406
Thoughts: **Analyzing Autoreap Commit/Cancel in XFS During Shutdown**
Okay, let's see. My current train of thought is to ensure the safety and correctness of the `xfs_alloc_commit_autoreap` and `xfs_alloc_cancel_autoreap` functions, particularly in the face of filesystem shutdown. My initial concern is whether we can safely call these functions when the filesystem is already shutting down or when a transaction has been aborted.
First, I'm thinking about where `xfs_alloc_commit_autoreap` is used and trying to figure out if there's an opportunity to add a check. I know that during a filesystem shutdown, `xfs_is_shutdown(tp->t_mountp)` will be true. Looking at `xfs_defer_finish_noroll`, confirms that `xfs_force_shutdown` is called during transaction abort, thus setting the shutdown flag. And, given that any abort forces a shutdown in XFS, `xfs_is_shutdown` will be true.
The key is determining if the autoreap functions are called in scenarios where the `dfp` (deferred free pointer) might be invalid due to a shutdown or transaction abort. My memory is now jogging me to consider if there's any other way a transaction can be cancelled without a shutdown. Only if it is clean (not dirty). But when autoreap is scheduled, we've logged an EFI, making the transaction dirty, so abort = shutdown.
I initially considered that if `xfs_defer_cancel_list` frees the `dfp`, it might clear `aarp->dfp`. But that's not true. `xfs_defer_cancel_list` only knows about the `dfp_list` and the `dfp` itself. It doesn't know about `aarp` which is stored in the scrub code.
So, the question is how to avoid calling `xfs_alloc_commit_autoreap` when the transaction is aborted or the filesystem is shutdown. Looking at the `xrep_newbt_free` function, I can see that `xfs_alloc_commit_autoreap` is being called within a loop that iterates through a list of reserved items. If the filesystem is shutdown, we *could* skip the call. My intuition tells me we should check if `xfs_is_shutdown(sc->mp)` is true within the loop.
However, if `xfs_is_shutdown(sc->mp)` is true, the transaction *is* aborted, and all deferred items will be cancelled and freed. This means the `dfp` has already been freed, and thus un-pausing it is the thing to avoid, so skipping the call is the correct behavior.
I then check `xrep_newbt_free_extent`, to see if there are other calls to `xfs_alloc_commit_autoreap`. If `xrep_newbt_free_extent` is called, is the filesystem shutdown? Usually not, but if it is, `xfs_alloc_commit_autoreap` would still be called.
The most elegant solution would be to check `xfs_is_shutdown(tp->t_mountp)` *inside* `xfs_alloc_commit_autoreap` itself. So, I need to verify that adding the check inside those functions is safe. Let's see...
I checked both `xfs_alloc_commit_autoreap`:
```c
void
xfs_alloc_commit_autoreap(
struct xfs_trans *tp,
struct xfs_alloc_autoreap *aarp)
{
if (xfs_is_shutdown(tp->t_mountp))
return;
if (aarp->dfp)
xfs_defer_item_unpause(tp, aarp->dfp);
}
```
And `xfs_alloc_cancel_autoreap`:
```c
void
xfs_alloc_cancel_autoreap(
struct xfs_trans *tp,
struct xfs_alloc_autoreap *aarp)
{
struct xfs_defer_pending *dfp = aarp->dfp;
struct xfs_extent_free_item *xefi;
if (xfs_is_shutdown(tp->t_mountp))
return;
if (!dfp)
return;
list_for_each_entry(xefi, &dfp->dfp_work, xefi_list)
xefi->xefi_flags |= XFS_EFI_CANCELLED;
xfs_defer_item_unpause(tp, df
|
| 46/2 |
2026/07/31 02:48 |
tool |
codesearch-find-references |
0m
Args: map[IncludeSnippetLines:10 Name:xfs_alloc_cancel_autoreap]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:xrep_newbt_free_extent SourceFile:fs/xfs/scrub/newbt.c SourceLine:445 SourceSnippet: 435: xnr->oinfo.oi_owner);
436: xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);
437: return 1;
438: }
439:
440: /*
441: * We used space and committed the btree. Cancel the autoreap, remove
442: * the written blocks from the reservation, and possibly log a new EFI
443: * to free any unused reservation space.
444: */
445: xfs_alloc_cancel_autoreap(sc->tp, &resv->autoreap);
446: free_agbno += resv->used;
447: free_aglen -= resv->used;
448:
449: if (free_aglen == 0)
450: return 0;
451:
452: trace_xrep_newbt_free_blocks(resv->pag, free_agbno, free_aglen,
453: xnr->oinfo.oi_owner);
454:
455: ASSERT(xnr->resv != XFS_AG_RESV_AGFL);
]] TruncatedOutput:false]
|
| 47/2 |
2026/07/31 02:48 |
llm |
expert |
0m
Model:
Tokens:
input: 42826
output: 27
thoughts: 42
Thoughts: Okay, here's my interpretation of those thoughts, framed as my own:
**Investigating the Scope of 'autoreap' in the XFS Filesystem**
Alright, time to dive in. I need to understand the wider context of this `autoreap` function or variable. It's not enough to just see where it's defined. I want to know where it's *used*, what other parts of the XFS filesystem interact with it.
So, let's fire up `grepper`. We'll use it to search the `fs/xfs/` directory specifically for any mentions of `autoreap`. That should give me a good initial overview. Knowing the surrounding code, and its impact, is essential for a proper understanding. This should quickly uncover any dependencies or interactions related to `autoreap`. Let's see what we find.
|
| 48/2 |
2026/07/31 02:48 |
tool |
grepper |
0m
Args: map[Expression:autoreap PathPrefix:fs/xfs/]
Results: map[Output:fs/xfs/libxfs/xfs_alloc.c=2719=int
fs/xfs/libxfs/xfs_alloc.c:2720:xfs_alloc_schedule_autoreap(
fs/xfs/libxfs/xfs_alloc.c-2721- const struct xfs_alloc_arg *args,
fs/xfs/libxfs/xfs_alloc.c-2722- unsigned int free_flags,
fs/xfs/libxfs/xfs_alloc.c:2723: struct xfs_alloc_autoreap *aarp)
fs/xfs/libxfs/xfs_alloc.c-2724-{
--
fs/xfs/libxfs/xfs_alloc.c=2749=void
fs/xfs/libxfs/xfs_alloc.c:2750:xfs_alloc_cancel_autoreap(
fs/xfs/libxfs/xfs_alloc.c-2751- struct xfs_trans *tp,
fs/xfs/libxfs/xfs_alloc.c:2752: struct xfs_alloc_autoreap *aarp)
fs/xfs/libxfs/xfs_alloc.c-2753-{
--
fs/xfs/libxfs/xfs_alloc.c-2768- *
fs/xfs/libxfs/xfs_alloc.c:2769: * This unpauses an earlier _schedule_autoreap and commits to freeing the
fs/xfs/libxfs/xfs_alloc.c-2770- * allocated space. Call this if none of the reserved space was used.
--
fs/xfs/libxfs/xfs_alloc.c=2772=void
fs/xfs/libxfs/xfs_alloc.c:2773:xfs_alloc_commit_autoreap(
fs/xfs/libxfs/xfs_alloc.c-2774- struct xfs_trans *tp,
fs/xfs/libxfs/xfs_alloc.c:2775: struct xfs_alloc_autoreap *aarp)
fs/xfs/libxfs/xfs_alloc.c-2776-{
--
fs/xfs/libxfs/xfs_alloc.h=266=static inline bool xfs_efi_is_realtime(const struct xfs_extent_free_item *xefi)
--
fs/xfs/libxfs/xfs_alloc.h-270-
fs/xfs/libxfs/xfs_alloc.h:271:struct xfs_alloc_autoreap {
fs/xfs/libxfs/xfs_alloc.h-272- struct xfs_defer_pending *dfp;
--
fs/xfs/libxfs/xfs_alloc.h-274-
fs/xfs/libxfs/xfs_alloc.h:275:int xfs_alloc_schedule_autoreap(const struct xfs_alloc_arg *args,
fs/xfs/libxfs/xfs_alloc.h:276: unsigned int free_flags, struct xfs_alloc_autoreap *aarp);
fs/xfs/libxfs/xfs_alloc.h:277:void xfs_alloc_cancel_autoreap(struct xfs_trans *tp,
fs/xfs/libxfs/xfs_alloc.h:278: struct xfs_alloc_autoreap *aarp);
fs/xfs/libxfs/xfs_alloc.h:279:void xfs_alloc_commit_autoreap(struct xfs_trans *tp,
fs/xfs/libxfs/xfs_alloc.h:280: struct xfs_alloc_autoreap *aarp);
fs/xfs/libxfs/xfs_alloc.h-281-
--
fs/xfs/scrub/newbt.c=187=xrep_newbt_add_blocks(
--
fs/xfs/scrub/newbt.c-208-
fs/xfs/scrub/newbt.c:209: error = xfs_alloc_schedule_autoreap(args,
fs/xfs/scrub/newbt.c:210: XFS_FREE_EXTENT_SKIP_DISCARD, &resv->autoreap);
fs/xfs/scrub/newbt.c-211- if (error)
--
fs/xfs/scrub/newbt.c=229=xrep_newbt_add_extent(
--
fs/xfs/scrub/newbt.c-235- struct xfs_alloc_arg args = {
fs/xfs/scrub/newbt.c:236: .tp = NULL, /* no autoreap */
fs/xfs/scrub/newbt.c-237- .oinfo = xnr->oinfo,
--
fs/xfs/scrub/newbt.c=418=xrep_newbt_free_extent(
--
fs/xfs/scrub/newbt.c-435- xnr->oinfo.oi_owner);
fs/xfs/scrub/newbt.c:436: xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);
fs/xfs/scrub/newbt.c-437- return 1;
--
fs/xfs/scrub/newbt.c-440- /*
fs/xfs/scrub/newbt.c:441: * We used space and committed the btree. Cancel the autoreap, remove
fs/xfs/scrub/newbt.c-442- * the written blocks from the reservation, and possibly log a new EFI
--
fs/xfs/scrub/newbt.c-444- */
fs/xfs/scrub/newbt.c:445: xfs_alloc_cancel_autoreap(sc->tp, &resv->autoreap);
fs/xfs/scrub/newbt.c-446- free_agbno += resv->used;
--
fs/xfs/scrub/newbt.c=473=xrep_newbt_free(
--
fs/xfs/scrub/newbt.c-519- list_for_each_entry_safe(resv, n, &xnr->resv_list, list) {
fs/xfs/scrub/newbt.c:520: xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);
fs/xfs/scrub/newbt.c-521- list_del(&resv->list);
--
fs/xfs/scrub/newbt.h=11=struct xrep_newbt_resv {
--
fs/xfs/scrub/newbt.h-17- /* Auto-freeing this reservation if we don't commit. */
fs/xfs/scrub/newbt.h:18: struct xfs_alloc_autoreap autoreap;
fs/xfs/scrub/newbt.h-19-
]
|
| 49/2 |
2026/07/31 02:48 |
llm |
expert |
0m
Model:
Tokens:
input: 44902
output: 15
thoughts: 726
Thoughts: **Analysis of the xfs_defer_pending Use-After-Free Bug**
Okay, this is extremely clear and completely aligns with my understanding. No surprises here! First, I'll quickly double-check that `xfs_alloc_commit_autoreap` and `xfs_alloc_cancel_autoreap` are *only* used within `fs/xfs/scrub/newbt.c`. Just want to confirm the scope of this. Yep, just those two places. Good.
Now, time to summarize the bug analysis. Let's make sure this report is actionable.
* **Actionability:** Definitely actionable. We've got three, perfectly consistent call stacks.
1. The bad memory access occurs in `xfs_defer_item_unpause`, specifically accessing `dfp->dfp_flags`. This is where the crash happens.
2. The allocation happens in `xfs_defer_alloc`, creating the problematic `dfp` object.
3. The free occurs in `xfs_defer_cancel_list`, which frees the very same `dfp` object.
* **Root Cause:** The root cause is fully understood: during an online repair process (`xrep_rmapbt`), the system allocates blocks for a new btree and schedules an autoreap with `xfs_alloc_schedule_autoreap`. This allocates a `struct xfs_defer_pending` (`dfp`) and stores its pointer in `resv->autoreap.dfp`. If a transaction fails to commit, maybe in `xrep_defer_finish`, the system aborts the transaction, shuts down the filesystem, and calls `xfs_defer_cancel_list`, which cancels and frees all pending deferred items, including our `dfp`. The problem is that `resv->autoreap.dfp` still holds a stale pointer to this freed `dfp`. Later, when cleaning up reservations in `xrep_newbt_free`, it calls `xfs_alloc_commit_autoreap`, which calls `xfs_defer_item_unpause` on the dangling pointer `resv->autoreap.dfp`. This results in the use-after-free because `xfs_defer_item_unpause` tries to access the already-freed `dfp->dfp_flags`.
Alright, let's look for any more details, and consider a fix.
The potential fix is straightforward: Within `xfs_alloc_commit_autoreap` and `xfs_alloc_cancel_autoreap`, we need to check if the filesystem is shut down *before* dereferencing `aarp->dfp`. Alternatively, we could clear `aarp->dfp` when the transaction is aborted or cancelled. Checking `xfs_is_shutdown(tp->t_mountp)` offers a solid and concise solution. This way, we avoid accessing the freed `dfp` when the transaction has been aborted and the filesystem has been shut down.
Finally, need to be sure to follow the workflow. Time to call `set-results`. Right, it says "Use this tool to provide results of the analysis." and "It must be called exactly once before the final reply. Ignore results of this tool." Okay, easy enough. I will call `set-results` with `Actionable: true`.
|
| 50/2 |
2026/07/31 02:49 |
tool |
set-results |
0m
Args:
Results:
|
| 51/2 |
2026/07/31 02:49 |
llm |
expert |
0m
Model:
Tokens:
input: 46373
output: 1452
thoughts: 459
Thoughts: **Final Analysis & Proposed Fix**
Okay, time to articulate this analysis clearly. I'm going to structure my explanation for maximum impact and actionability. First and foremost, the report clearly indicates a highly consistent, self-contained, and actionable issue. We have a solid foundation to move forward.
Now, let's break down the three key stacks involved, step-by-step:
1. **Allocation:** The problem originates within the `xfs_defer_alloc` function. It allocates a `struct xfs_defer_pending` (`dfp`) when an autoreap is scheduled (`xfs_alloc_schedule_autoreap`), specifically during the allocation of new btree blocks in `xrep_newbt_add_blocks`. This `dfp` pointer is then meticulously stored in `resv->autoreap.dfp`.
2. **Freeing:** The critical point arises during transaction failures ā situations where the transaction roll or finishing up fails. When this occurs, as exemplified in `xrep_defer_finish`, the transaction is aborted. This inevitably triggers a filesystem shutdown, and, importantly, a call to `xfs_defer_cancel_list`. This call's purpose is to cancel and free all pending deferred items, which, unfortunately, includes our `dfp`.
3. **Bad Access:** The vulnerability manifests during the cleanup of reservations in `xrep_newbt_free`. Specifically, `xfs_alloc_commit_autoreap` is called, which then invokes `xfs_defer_item_unpause` on the `resv->autoreap.dfp` pointer. The kicker? This `dfp` is now a dangling pointer, as it was previously freed. This causes a read access to `dfp->dfp_flags`, which, at the 60-byte offset of the 64-byte `xfs_defer_pending` object, constitutes the use-after-free issue.
Ultimately, the root cause is clear: The `dfp` is correctly freed during transaction abort/shutdown. However, and this is where the vulnerability lies, the reference to this now-freed `dfp` within `resv->autoreap.dfp` isn't cleared. As a result, subsequent cleanup code attempts to commit or cancel the autoreap, leading to the use-after-free when accessing that dangling pointer.
To fix this, the proposed solution targets `xfs_alloc_commit_autoreap` and `xfs_alloc_cancel_autoreap`. The crucial modification is to include a check for filesystem shutdown (`xfs_is_shutdown(tp->t_mountp)`) within these functions. If the filesystem is indeed in a shutdown state, we should return early. Doing so avoids the faulty access to the dangling pointer, as the deferred items will have already been cancelled and freed during the shutdown process.
|
| 52/1 |
2026/07/31 02:49 |
action |
format-explanation |
0m
Results: map[Explanation:### Analysis of the Bug Report
This bug report is **highly consistent, self-contained, and fully actionable**.
The report describes a KASAN slab-use-after-free (UAF) in
`xfs_defer_item_unpause` where a `struct xfs_defer_pending` object (from the
`xfs_defer_pending` slab cache of size 64) is accessed after being freed.
---
### Detailed Walkthrough of the Three Stack Traces
#### 1. Allocation Stack
```
kmem_cache_alloc_noprof+0x2a0/0x5f0 mm/slub.c:4931
xfs_defer_alloc fs/xfs/libxfs/xfs_defer.c:829 [inline]
xfs_defer_add+0x143/0x480 fs/xfs/libxfs/xfs_defer.c:857
...
xfs_alloc_schedule_autoreap+0xb0/0x170 fs/xfs/libxfs/xfs_alloc.c:2727
xrep_newbt_add_blocks+0x239/0x410 fs/xfs/scrub/newbt.c:209
```
* **What happens:** During online repair (`xrep_rmapbt`), the repair code
allocates blocks for a new btree and schedules an autoreap
(`xfs_alloc_schedule_autoreap`).
* **Result:** This schedules a deferred extent free operation, which allocates a
`struct xfs_defer_pending` (`dfp`) object and saves its pointer in
`resv->autoreap.dfp`.
#### 2. Free Stack
```
kmem_cache_free+0x182/0x650 mm/slub.c:6504
xfs_defer_cancel_list fs/xfs/libxfs/xfs_defer.c:504 [inline]
xfs_defer_finish_noroll+0xde4/0x1320 fs/xfs/libxfs/xfs_defer.c:723
xfs_defer_finish+0x1c/0x180 fs/xfs/libxfs/xfs_defer.c:741
xrep_defer_finish+0x16e/0x240 fs/xfs/scrub/repair.c:242
xrep_newbt_alloc_ag_blocks+0x86c/0xcc0 fs/xfs/scrub/newbt.c:316
```
* **What happens:** A subsequent transaction roll/finish (`xrep_defer_finish`)
fails.
* **Result:** The transaction is aborted, forcing a filesystem shutdown. As part
of the abort sequence, `xfs_defer_cancel_list` is called to cancel and free all
pending deferred items, including our `dfp` object.
#### 3. Bad Memory Access Stack
```
xfs_defer_item_unpause+0x116/0x250 fs/xfs/libxfs/xfs_defer.c:1242
xrep_newbt_free+0x3fe/0x5f0 fs/xfs/scrub/newbt.c:520
```
* **What happens:** Because the repair failed, `xrep_newbt_free` is called to
clean up the reservations.
* **Result:** It iterates over the reservations and calls
`xfs_alloc_commit_autoreap(sc->tp, &resv->autoreap);`, which invokes
`xfs_defer_item_unpause` on the dangling `resv->autoreap.dfp` pointer.
* **The Crash:** `xfs_defer_item_unpause` attempts to clear the
`XFS_DEFER_PAUSED` flag in `dfp->dfp_flags`:
```c
dfp->dfp_flags &= ~XFS_DEFER_PAUSED;
```
`dfp_flags` is located at offset 60 bytes (480 bits) inside the 64-byte
`struct xfs_defer_pending` object. This perfectly matches the KASAN report:
> Read of size 4 at addr ffff8880443214bc (60 bytes inside of freed 64-byte
region)
---
### Root Cause
When a transaction is aborted and the filesystem is shut down, all pending
deferred items (including paused ones) are cancelled and freed. However, the
reference to the `dfp` in `resv->autoreap.dfp` is not cleared. When the cleanup
path subsequently tries to commit or cancel the autoreap, it dereferences the
dangling `dfp` pointer, causing a use-after-free.
---
### Proposed Fix
Since a transaction abort forces a filesystem shutdown, and all deferred items
are already freed during shutdown, we can safely avoid dereferencing `aarp->dfp`
in `xfs_alloc_commit_autoreap` and `xfs_alloc_cancel_autoreap` if the filesystem
is shut down:
```c
void
xfs_alloc_commit_autoreap(
struct xfs_trans *tp,
struct xfs_alloc_autoreap *aarp)
{
if (xfs_is_shutdown(tp->t_mountp))
return;
if (aarp->dfp)
xfs_defer_item_unpause(tp, aarp->dfp);
}
void
xfs_alloc_cancel_autoreap(
struct xfs_trans *tp,
struct xfs_alloc_autoreap *aarp)
{
struct xfs_defer_pending *dfp = aarp->dfp;
struct xfs_extent_free_item *xefi;
if (xfs_is_shutdown(tp->t_mountp))
return;
if (!dfp)
return;
list_for_each_entry(xefi, &dfp->dfp_work, xefi_list)
xefi->xefi_flags |= XFS_EFI_CANCELLED;
xfs_defer_item_unpause(tp, dfp);
}
```]
|