possible deadlock in ocfs2_duplicate_inline_data

Status: upstream: reported C repro on 2026/11/14 08:26
Subsystems: ocfs2
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+3f66416993279938e957@syzkaller.appspotmail.com
First crash: 1h27m, last: 21m
✨ AI-generated root cause summary:

In fs/ocfs2/xattr.c, OCFS2_IP_ALLOC_SEM_UNPUBLISHED was defined as 1 to allow down_write_nested(&OCFS2_I(inode)->ip_alloc_sem, ...) within an active transaction during inode creation without tripping lockdep against the standard ip_alloc_sem -> transaction lock order. However, subclass 1 (SINGLE_DEPTH_NESTING) was already in use by ocfs2_remap_file_range() in fs/ocfs2/file.c when locking the destination inode's ip_alloc_sem. When ocfs2_remap_file_range() locks the destination inode under subclass 1 and invokes ocfs2_reflink_remap_blocks() -> ocfs2_duplicate_inline_data(), ocfs2_start_trans() is called, acquiring sb_internal and j_trans_barrier; lockdep sees both transaction -> ip_alloc_sem/1 and ip_alloc_sem/1 -> transaction, reporting a circular locking dependency false positive due to the subclass collision.

▶ ▼ ✨ Full AI root cause analysis
Based on kernel commit 97d73c825122:

Root Cause Analysis

1. Functions, Structs, and Files Involved

  • fs/ocfs2/xattr.c:
    • enum { OCFS2_IP_ALLOC_SEM_UNPUBLISHED = 1 } (defines the lockdep subclass for unpublished inodes).
    • ocfs2_xattr_set_handle(): acquires down_write_nested(&OCFS2_I(inode)->ip_alloc_sem, OCFS2_IP_ALLOC_SEM_UNPUBLISHED).
  • fs/ocfs2/file.c:
    • ocfs2_remap_file_range(): locks source and destination file allocation semaphores, taking down_write_nested(&OCFS2_I(inode_out)->ip_alloc_sem, SINGLE_DEPTH_NESTING).
  • fs/ocfs2/refcounttree.c:
    • ocfs2_reflink_remap_blocks() / ocfs2_duplicate_inline_data(): starts a transaction while holding the allocation semaphores.
  • fs/ocfs2/journal.c:
    • ocfs2_start_trans(): starts a transaction, acquiring sb_internal via sb_start_intwrite(osb->sb) and down_read(&osb->journal->j_trans_barrier).
  • include/linux/lockdep.h:
    • #define SINGLE_DEPTH_NESTING 1.

2. Detailed Technical Mechanism

In OCFS2, the canonical locking order between the allocation semaphore (oi->ip_alloc_sem) and filesystem journal transactions is: $$\text{inode->ip_alloc_sem} \longrightarrow \text{transaction (sb_internal / j_trans_barrier)}$$

  1. Transaction $\rightarrow$ ip_alloc_sem dependency in inode creation (ocfs2_xattr_set_handle): During inode creation paths (e.g. ocfs2_mknod, ocfs2_mkdir, ocfs2_symlink), a transaction is already active when security xattrs and ACLs are initialized (ocfs2_init_security_set() / ocfs2_init_acl()). Inside ocfs2_xattr_set_handle(), ip_alloc_sem is acquired:

    down_write_nested(&OCFS2_I(inode)->ip_alloc_sem,
                  OCFS2_IP_ALLOC_SEM_UNPUBLISHED);

    To avoid lockdep detecting a reverse dependency (transaction -> ip_alloc_sem) against the normal ip_alloc_sem -> transaction order used during truncation and allocation, OCFS2_IP_ALLOC_SEM_UNPUBLISHED was introduced. However, it was defined as:

    enum {
    OCFS2_IP_ALLOC_SEM_UNPUBLISHED = 1,
};

    This assigned lockdep subclass 1 (&ocfs2_file_ip_alloc_sem_key/1) to the semaphore. As a result, lockdep registered the dependency chain: $$\text{sb_internal} \longrightarrow \text{journal->j_trans_barrier} \longrightarrow \text{&ocfs2_file_ip_alloc_sem_key/1}$$

  2. Subclass collision in ocfs2_remap_file_range(): When remapping file ranges across two distinct inodes (same_inode == false), ocfs2_remap_file_range() locks the allocation semaphore for both inodes:

    down_write(&OCFS2_I(inode_in)->ip_alloc_sem);
if (!same_inode)
    down_write_nested(&OCFS2_I(inode_out)->ip_alloc_sem,
                      SINGLE_DEPTH_NESTING);

    Because SINGLE_DEPTH_NESTING is #define SINGLE_DEPTH_NESTING 1, inode_out->ip_alloc_sem is also acquired with subclass 1 (&ocfs2_file_ip_alloc_sem_key/1).

  3. Subsequent transaction start: With both inode_in->ip_alloc_sem (subclass 0) and inode_out->ip_alloc_sem (subclass 1) held, ocfs2_remap_file_range() calls ocfs2_reflink_remap_blocks(). When remapping inline data, it invokes ocfs2_duplicate_inline_data(), which calls:

    handle = ocfs2_start_trans(osb, OCFS2_INODE_UPDATE_CREDITS);

    ocfs2_start_trans() attempts to acquire:

    sb_start_intwrite(osb->sb); /* acquires sb_internal */
down_read(&osb->journal->j_trans_barrier);

Because lockdep treats OCFS2_IP_ALLOC_SEM_UNPUBLISHED and SINGLE_DEPTH_NESTING as the exact same lock class (&ocfs2_file_ip_alloc_sem_key/1), it observes:

  • Chain 1 (from mknod): sb_internal -> j_trans_barrier -> ip_alloc_sem/1
  • Chain 2 (from remap_file_range): ip_alloc_sem/1 -> sb_internal

Lockdep flags this as a possible circular locking dependency (ABBA deadlock).

3. Invariant Violation and Conclusion

  • Classification: False positive lockdep warning caused by lockdep subclass namespace collision.
  • Why no real deadlock occurs: The inode locked via OCFS2_IP_ALLOC_SEM_UNPUBLISHED in ocfs2_xattr_set_handle() is newly allocated, unpublished, unhashed, and not yet linked to any directory entry. It is completely inaccessible to concurrent threads, making concurrent contention between ocfs2_xattr_set_handle() and ocfs2_remap_file_range() on the same inode impossible.
  • Remedy: Assign OCFS2_IP_ALLOC_SEM_UNPUBLISHED a distinct subclass index that does not collide with SINGLE_DEPTH_NESTING (e.g., subclass 2).
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
c94b1ede assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ FuzzingArtifact: ❌ MemoryCorruption: ❌ NetworkNeedsSetup: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in ocfs2_duplicate_inline_data 2026/11/14 07:19 2026/11/14 07:20 2026/11/14 08:07 819ebe34
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [ocfs2?] possible deadlock in ocfs2_duplicate_inline_data 0 (1) 2026/11/14 08:26

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor238/5619 is trying to acquire lock:
ffff88803fb38818 (sb_internal#2){.+.+}-{0:0}, at: ocfs2_duplicate_inline_data+0x16a/0x570 fs/ocfs2/refcounttree.c:3991

but task is already holding lock:
ffff88803559db90 (&oi->ip_alloc_sem/1){+.+.}-{4:4}, at: ocfs2_remap_file_range+0x342/0x700 fs/ocfs2/file.c:2780

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&oi->ip_alloc_sem/1){+.+.}-{4:4}:
       down_write_nested+0x39/0x50 kernel/locking/rwsem.c:1757
       ocfs2_xattr_set_handle+0x3fc/0x820 fs/ocfs2/xattr.c:3941
       ocfs2_init_security_set+0x151/0x210 fs/ocfs2/xattr.c:7996
       ocfs2_mknod+0x13dd/0x2190 fs/ocfs2/namei.c:422
       ocfs2_create+0x195/0x460 fs/ocfs2/namei.c:677
       lookup_open+0x103d/0x1b00 fs/namei.c:4575
       open_last_lookups fs/namei.c:4774 [inline]
       path_openat+0x711/0x2100 fs/namei.c:5013
       do_file_open+0x23e/0x4a0 fs/namei.c:5045
       do_sys_openat2+0x115/0x200 fs/open.c:1443
       do_sys_open fs/open.c:1449 [inline]
       __do_sys_creat fs/open.c:1527 [inline]
       __se_sys_creat fs/open.c:1521 [inline]
       __x64_sys_creat+0x8f/0xc0 fs/open.c:1521
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&journal->j_trans_barrier){.+.+}-{4:4}:
       down_read+0x92/0x200 kernel/locking/rwsem.c:1574
       ocfs2_start_trans+0x3aa/0x700 fs/ocfs2/journal.c:379
       ocfs2_block_group_alloc fs/ocfs2/suballoc.c:801 [inline]
       ocfs2_reserve_suballoc_bits+0x7b7/0x4850 fs/ocfs2/suballoc.c:950
       ocfs2_reserve_new_metadata_blocks+0x415/0x9a0 fs/ocfs2/suballoc.c:1100
       ocfs2_mknod+0xe79/0x2190 fs/ocfs2/namei.c:350
       ocfs2_create+0x195/0x460 fs/ocfs2/namei.c:677
       lookup_open+0x103d/0x1b00 fs/namei.c:4575
       open_last_lookups fs/namei.c:4774 [inline]
       path_openat+0x711/0x2100 fs/namei.c:5013
       do_file_open+0x23e/0x4a0 fs/namei.c:5045
       do_sys_openat2+0x115/0x200 fs/open.c:1443
       do_sys_open fs/open.c:1449 [inline]
       __do_sys_creat fs/open.c:1527 [inline]
       __se_sys_creat fs/open.c:1521 [inline]
       __x64_sys_creat+0x8f/0xc0 fs/open.c:1521
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_internal#2){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3209 [inline]
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
       lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
       percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
       percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
       __sb_start_write include/linux/fs/super.h:19 [inline]
       sb_start_intwrite include/linux/fs/super.h:177 [inline]
       ocfs2_start_trans+0x2a7/0x700 fs/ocfs2/journal.c:377
       ocfs2_duplicate_inline_data+0x16a/0x570 fs/ocfs2/refcounttree.c:3991
       ocfs2_reflink_remap_blocks+0x4aa/0x1ab0 fs/ocfs2/refcounttree.c:4684
       ocfs2_remap_file_range+0x457/0x700 fs/ocfs2/file.c:2788
       vfs_copy_file_range+0xe39/0x1430 fs/read_write.c:1581
       __do_sys_copy_file_range fs/read_write.c:1664 [inline]
       __se_sys_copy_file_range+0x2fb/0x480 fs/read_write.c:1631
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  sb_internal#2 --> &journal->j_trans_barrier --> &oi->ip_alloc_sem/1

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&oi->ip_alloc_sem/1);
                               lock(&journal->j_trans_barrier);
                               lock(&oi->ip_alloc_sem/1);
  rlock(sb_internal#2);

 *** DEADLOCK ***

locks held by syz-executor238/5619: 5, on CPU#0:
 #0: ffff88803fb38528 (sb_writers#8){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2765 [inline]
 #0: ffff88803fb38528 (sb_writers#8){.+.+}-{0:0}, at: vfs_copy_file_range+0xa29/0x1430 fs/read_write.c:1569
 #1: ffff88803559ce80 (&sb->s_type->i_mutex_key#17){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1027 [inline]
 #1: ffff88803559ce80 (&sb->s_type->i_mutex_key#17){+.+.}-{4:4}, at: lock_two_nondirectories+0xe7/0x180 fs/inode.c:1275
 #2: ffff88803559df40 (&sb->s_type->i_mutex_key#17/4){+.+.}-{4:4}, at: ocfs2_reflink_inodes_lock+0x11a/0xc20 fs/ocfs2/refcounttree.c:4772
 #3: ffff88803559cad0 (&oi->ip_alloc_sem#2){++++}-{4:4}, at: ocfs2_remap_file_range+0x31e/0x700 fs/ocfs2/file.c:2778
 #4: ffff88803559db90 (&oi->ip_alloc_sem/1){+.+.}-{4:4}, at: ocfs2_remap_file_range+0x342/0x700 fs/ocfs2/file.c:2780

stack backtrace:
CPU: 0 UID: 0 PID: 5619 Comm: syz-executor238 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/06/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
 check_prev_add kernel/locking/lockdep.c:3209 [inline]
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
 percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
 __sb_start_write include/linux/fs/super.h:19 [inline]
 sb_start_intwrite include/linux/fs/super.h:177 [inline]
 ocfs2_start_trans+0x2a7/0x700 fs/ocfs2/journal.c:377
 ocfs2_duplicate_inline_data+0x16a/0x570 fs/ocfs2/refcounttree.c:3991
 ocfs2_reflink_remap_blocks+0x4aa/0x1ab0 fs/ocfs2/refcounttree.c:4684
 ocfs2_remap_file_range+0x457/0x700 fs/ocfs2/file.c:2788
 vfs_copy_file_range+0xe39/0x1430 fs/read_write.c:1581
 __do_sys_copy_file_range fs/read_write.c:1664 [inline]
 __se_sys_copy_file_range+0x2fb/0x480 fs/read_write.c:1631
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fee8fd74a09
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 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 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffecd787a88 EFLAGS: 00000246 ORIG_RAX: 0000000000000146
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fee8fd74a09
RDX: 0000000000000004 RSI: 0000200000004d40 RDI: 0000000000000005
RBP: 0000000000000001 R08: fffffffffffffff8 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffecd787ac0
R13: 0000000000000002 R14: 431bde82d7b634db R15: 00007fee8fdd404b
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/11/14 08:26 upstream 97d73c825122 819ebe34 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci2-upstream-fs possible deadlock in ocfs2_duplicate_inline_data
2026/11/14 07:19 upstream 97d73c825122 819ebe34 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in ocfs2_duplicate_inline_data
* Struck through repros no longer work on HEAD.