syzbot


possible deadlock in do_page_mkwrite (3)

Status: upstream: reported on 2025/06/15 09:03
Subsystems: kernfs
[Documentation on labels]
Reported-by: syzbot+47c7d1a51f51d13f5723@syzkaller.appspotmail.com
First crash: 76d, last: 16h47m
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [kernfs?] possible deadlock in do_page_mkwrite (3) 0 (1) 2025/06/15 09:03
Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in do_page_mkwrite (2) dri 4 5 209d 269d 0/29 auto-obsoleted due to no activity on 2025/05/09 03:36
linux-6.1 possible deadlock in do_page_mkwrite origin:upstream missing-backport 4 C done 12 186d 850d 0/3 upstream: reported C repro on 2023/04/29 03:26
upstream possible deadlock in do_page_mkwrite fs 4 C error done 114 574d 988d 0/29 auto-obsoleted due to no activity on 2024/04/09 15:57
linux-5.15 possible deadlock in do_page_mkwrite missing-backport origin:upstream 4 C done 15 9d03h 806d 0/3 upstream: reported C repro on 2023/06/12 00:09

Sample crash report:
BTRFS info (device loop8): force clearing of disk cache
BTRFS info (device loop8): use zstd compression, level 3
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.8.601/11635 is trying to acquire lock:
ffff8880315aa600 (sb_pagefaults#2){.+.+}-{0:0}, at: do_page_mkwrite+0x14d/0x310 mm/memory.c:3361

but task is already holding lock:
ffff88801988c238 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x267/0x870 fs/kernfs/dir.c:1893

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&root->kernfs_rwsem){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       down_write+0x3a/0x50 kernel/locking/rwsem.c:1590
       kernfs_add_one+0x41/0x520 fs/kernfs/dir.c:791
       kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1093
       sysfs_create_dir_ns+0x123/0x280 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x5a5/0xb50 lib/kobject.c:240
       kobject_add_varg lib/kobject.c:374 [inline]
       kobject_init_and_add+0x125/0x190 lib/kobject.c:457
       btrfs_sysfs_add_qgroups+0x111/0x2b0 fs/btrfs/sysfs.c:2641
       btrfs_quota_enable+0x253/0x2600 fs/btrfs/qgroup.c:1022
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3667
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/rtmutex_api.c:535 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:547
       btrfs_quota_enable+0x28e/0x2600 fs/btrfs/qgroup.c:1051
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3667
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       join_transaction+0x1a4/0xca0 fs/btrfs/transaction.c:321
       start_transaction+0x6b6/0x1620 fs/btrfs/transaction.c:705
       btrfs_quota_enable+0x281/0x2600 fs/btrfs/qgroup.c:1049
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3667
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5385
       __lock_release kernel/locking/lockdep.c:5574 [inline]
       lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889
       percpu_up_read include/linux/percpu-rwsem.h:112 [inline]
       __sb_end_write include/linux/fs.h:1793 [inline]
       sb_end_intwrite+0x26/0x1c0 include/linux/fs.h:1910
       __btrfs_end_transaction+0x248/0x640 fs/btrfs/transaction.c:1076
       btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6249
       inode_update_time fs/inode.c:2075 [inline]
       __file_update_time fs/inode.c:2304 [inline]
       file_update_time+0x34a/0x490 fs/inode.c:2334
       btrfs_page_mkwrite+0x5dd/0x1a80 fs/btrfs/file.c:1916
       do_page_mkwrite+0x14d/0x310 mm/memory.c:3361
       do_shared_fault mm/memory.c:5649 [inline]
       do_fault mm/memory.c:5711 [inline]
       do_pte_missing mm/memory.c:4234 [inline]
       handle_pte_fault mm/memory.c:6052 [inline]
       __handle_mm_fault mm/memory.c:6195 [inline]
       handle_mm_fault+0x124b/0x3400 mm/memory.c:6364
       do_user_addr_fault+0x764/0x1390 arch/x86/mm/fault.c:1387
       handle_page_fault arch/x86/mm/fault.c:1476 [inline]
       exc_page_fault+0x76/0xf0 arch/x86/mm/fault.c:1532
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623

-> #0 (sb_pagefaults#2){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       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.h:1798 [inline]
       sb_start_pagefault include/linux/fs.h:1963 [inline]
       btrfs_page_mkwrite+0x32c/0x1a80 fs/btrfs/file.c:1875
       do_page_mkwrite+0x14d/0x310 mm/memory.c:3361
       wp_page_shared mm/memory.c:3762 [inline]
       do_wp_page+0x25b8/0x4910 mm/memory.c:3981
       handle_pte_fault mm/memory.c:6068 [inline]
       __handle_mm_fault mm/memory.c:6195 [inline]
       handle_mm_fault+0x97c/0x3400 mm/memory.c:6364
       do_user_addr_fault+0x764/0x1390 arch/x86/mm/fault.c:1387
       handle_page_fault arch/x86/mm/fault.c:1476 [inline]
       exc_page_fault+0x76/0xf0 arch/x86/mm/fault.c:1532
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
       filldir64+0x2c7/0x690 fs/readdir.c:-1
       dir_emit include/linux/fs.h:3958 [inline]
       kernfs_fop_readdir+0x53a/0x870 fs/kernfs/dir.c:1910
       iterate_dir+0x3a2/0x580 fs/readdir.c:108
       __do_sys_getdents64 fs/readdir.c:410 [inline]
       __se_sys_getdents64+0xe4/0x260 fs/readdir.c:396
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  sb_pagefaults#2 --> &fs_info->qgroup_ioctl_lock --> &root->kernfs_rwsem

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&root->kernfs_rwsem);
                               lock(&fs_info->qgroup_ioctl_lock);
                               lock(&root->kernfs_rwsem);
  rlock(sb_pagefaults#2);

 *** DEADLOCK ***

4 locks held by syz.8.601/11635:
 #0: ffff8880359d0d28 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x253/0x320 fs/file.c:1232
 #1: ffff888061863ea8 (&type->i_mutex_dir_key#4){++++}-{4:4}, at: iterate_dir+0x29e/0x580 fs/readdir.c:101
 #2: ffff88801988c238 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x267/0x870 fs/kernfs/dir.c:1893
 #3: ffff88803de418d0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:472 [inline]
 #3: ffff88803de418d0 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:277 [inline]
 #3: ffff88803de418d0 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x32/0x300 mm/mmap_lock.c:337

stack backtrace:
CPU: 0 UID: 0 PID: 11635 Comm: syz.8.601 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 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.h:1798 [inline]
 sb_start_pagefault include/linux/fs.h:1963 [inline]
 btrfs_page_mkwrite+0x32c/0x1a80 fs/btrfs/file.c:1875
 do_page_mkwrite+0x14d/0x310 mm/memory.c:3361
 wp_page_shared mm/memory.c:3762 [inline]
 do_wp_page+0x25b8/0x4910 mm/memory.c:3981
 handle_pte_fault mm/memory.c:6068 [inline]
 __handle_mm_fault mm/memory.c:6195 [inline]
 handle_mm_fault+0x97c/0x3400 mm/memory.c:6364
 do_user_addr_fault+0x764/0x1390 arch/x86/mm/fault.c:1387
 handle_page_fault arch/x86/mm/fault.c:1476 [inline]
 exc_page_fault+0x76/0xf0 arch/x86/mm/fault.c:1532
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
RIP: 0010:filldir64+0x2c7/0x690 fs/readdir.c:379
Code: e8 48 8b 44 24 50 49 89 44 24 08 48 8b 4c 24 08 48 8b 44 24 58 48 89 01 48 8b 04 24 8b 54 24 14 49 bc 00 00 00 00 00 fc ff df <66> 89 41 10 80 e2 0f 88 51 12 49 63 ee c6 44 29 13 00 4c 8d 79 13
RSP: 0018:ffffc90010037c58 EFLAGS: 00050283
RAX: 0000000000000020 RBX: ffffc90010037e38 RCX: 0000200000000ff0
RDX: 0000000000000004 RSI: 0000200000000fd0 RDI: 0000200000001010
RBP: 00007ffffffff000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed1004c4c001 R12: dffffc0000000000
R13: ffffffff8b79a4c0 R14: 0000000000000005 R15: 0000200000001010
 dir_emit include/linux/fs.h:3958 [inline]
 kernfs_fop_readdir+0x53a/0x870 fs/kernfs/dir.c:1910
 iterate_dir+0x3a2/0x580 fs/readdir.c:108
 __do_sys_getdents64 fs/readdir.c:410 [inline]
 __se_sys_getdents64+0xe4/0x260 fs/readdir.c:396
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9e1304ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f9e112ae038 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007f9e13275fa0 RCX: 00007f9e1304ebe9
RDX: 0000000000000ff6 RSI: 0000200000000f80 RDI: 0000000000000008
RBP: 00007f9e130d1e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9e13276038 R14: 00007f9e13275fa0 R15: 00007ffea8a15208
 </TASK>
sysfs: Unknown parameter '˙˙˙˙˙˙˙˙˙˙˙˙˙˙18446744073709551615˙˙˙˙š@­LqE:†‹ á艞Őt}˛0ü$‰'
----------------
Code disassembly (best guess):
   0:	e8 48 8b 44 24       	call   0x24448b4d
   5:	50                   	push   %rax
   6:	49 89 44 24 08       	mov    %rax,0x8(%r12)
   b:	48 8b 4c 24 08       	mov    0x8(%rsp),%rcx
  10:	48 8b 44 24 58       	mov    0x58(%rsp),%rax
  15:	48 89 01             	mov    %rax,(%rcx)
  18:	48 8b 04 24          	mov    (%rsp),%rax
  1c:	8b 54 24 14          	mov    0x14(%rsp),%edx
  20:	49 bc 00 00 00 00 00 	movabs $0xdffffc0000000000,%r12
  27:	fc ff df
* 2a:	66 89 41 10          	mov    %ax,0x10(%rcx) <-- trapping instruction
  2e:	80 e2 0f             	and    $0xf,%dl
  31:	88 51 12             	mov    %dl,0x12(%rcx)
  34:	49 63 ee             	movslq %r14d,%rbp
  37:	c6 44 29 13 00       	movb   $0x0,0x13(%rcx,%rbp,1)
  3c:	4c 8d 79 13          	lea    0x13(%rcx),%r15

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/08/26 04:24 upstream b6add54ba618 bf27483f .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in do_page_mkwrite
2025/07/26 21:35 upstream 302f88ff3584 fb8f743d .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in do_page_mkwrite
2025/06/11 08:56 upstream aef17cb3d3c4 5d7e17ca .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in do_page_mkwrite
2025/06/11 08:56 upstream aef17cb3d3c4 5d7e17ca .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs possible deadlock in do_page_mkwrite
* Struck through repros no longer work on HEAD.