syzbot


possible deadlock in lookup_one_unlocked (2)

Status: moderation: reported on 2025/06/16 00:37
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+63d952994431b5f1104f@syzkaller.appspotmail.com
First crash: 22d, last: 22d
Similar bugs (1)
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in lookup_one_unlocked kernfs 1 456d 452d 0/29 closed as dup on 2024/04/09 14:58

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc1-syzkaller-00005-g488ef3560196 #0 Not tainted
------------------------------------------------------
syz.3.4164/22783 is trying to acquire lock:
ffff88801273bb38 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:882 [inline]
ffff88801273bb38 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}, at: lookup_slow fs/namei.c:1833 [inline]
ffff88801273bb38 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}, at: lookup_one_unlocked fs/namei.c:3016 [inline]
ffff88801273bb38 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}, at: lookup_one_unlocked+0xc7/0x120 fs/namei.c:3004

but task is already holding lock:
ffff88801273e3b0 (&ovl_i_mutex_dir_key[depth]#2){.+.+}-{4:4}, at: inode_lock_shared include/linux/fs.h:882 [inline]
ffff88801273e3b0 (&ovl_i_mutex_dir_key[depth]#2){.+.+}-{4:4}, at: lookup_slow fs/namei.c:1833 [inline]
ffff88801273e3b0 (&ovl_i_mutex_dir_key[depth]#2){.+.+}-{4:4}, at: walk_component+0x345/0x5b0 fs/namei.c:2138

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&ovl_i_mutex_dir_key[depth]#2){.+.+}-{4:4}:
       down_read+0x9b/0x480 kernel/locking/rwsem.c:1524
       inode_lock_shared include/linux/fs.h:882 [inline]
       lookup_slow fs/namei.c:1833 [inline]
       walk_component+0x345/0x5b0 fs/namei.c:2138
       lookup_last fs/namei.c:2639 [inline]
       path_lookupat+0x142/0x6d0 fs/namei.c:2663
       filename_lookup+0x224/0x5f0 fs/namei.c:2692
       kern_path+0x35/0x50 fs/namei.c:2825
       lookup_bdev+0xd8/0x280 block/bdev.c:1205
       resume_store+0x1d6/0x460 kernel/power/hibernate.c:1272
       kobj_attr_store+0x55/0x80 lib/kobject.c:840
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
       kernfs_fop_write_iter+0x351/0x510 fs/kernfs/file.c:334
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x6c4/0x1150 fs/read_write.c:686
       ksys_write+0x12a/0x250 fs/read_write.c:738
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
       __do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
       do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #3 (&of->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
       kernfs_fop_write_iter+0x28f/0x510 fs/kernfs/file.c:325
       iter_file_splice_write+0x91c/0x1150 fs/splice.c:738
       do_splice_from fs/splice.c:935 [inline]
       do_splice+0x1475/0x1fc0 fs/splice.c:1348
       __do_splice+0x32a/0x360 fs/splice.c:1430
       __do_sys_splice fs/splice.c:1633 [inline]
       __se_sys_splice fs/splice.c:1615 [inline]
       __ia32_sys_splice+0x189/0x250 fs/splice.c:1615
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
       __do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
       do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #2 (&pipe->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
       pipe_lock fs/pipe.c:91 [inline]
       pipe_lock+0x64/0x80 fs/pipe.c:88
       iter_file_splice_write+0x1ea/0x1150 fs/splice.c:683
       do_splice_from fs/splice.c:935 [inline]
       do_splice+0x1475/0x1fc0 fs/splice.c:1348
       __do_splice+0x32a/0x360 fs/splice.c:1430
       __do_sys_splice fs/splice.c:1633 [inline]
       __se_sys_splice fs/splice.c:1615 [inline]
       __ia32_sys_splice+0x189/0x250 fs/splice.c:1615
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
       __do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
       do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #1 (sb_writers#5){.+.+}-{0:0}:
       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:1793 [inline]
       sb_start_write include/linux/fs.h:1929 [inline]
       mnt_want_write+0x6f/0x450 fs/namespace.c:557
       ovl_create_object+0x12c/0x300 fs/overlayfs/dir.c:628
       lookup_open.isra.0+0x11d0/0x1580 fs/namei.c:3708
       open_last_lookups fs/namei.c:3807 [inline]
       path_openat+0x893/0x2cb0 fs/namei.c:4043
       do_filp_open+0x20b/0x470 fs/namei.c:4073
       do_sys_openat2+0x11b/0x1d0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_compat_sys_open fs/open.c:1505 [inline]
       __se_compat_sys_open fs/open.c:1503 [inline]
       __ia32_compat_sys_open+0x146/0x1e0 fs/open.c:1503
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
       __do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
       do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #0 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain kernel/locking/lockdep.c:3911 [inline]
       __lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5240
       lock_acquire kernel/locking/lockdep.c:5871 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5828
       down_read+0x9b/0x480 kernel/locking/rwsem.c:1524
       inode_lock_shared include/linux/fs.h:882 [inline]
       lookup_slow fs/namei.c:1833 [inline]
       lookup_one_unlocked fs/namei.c:3016 [inline]
       lookup_one_unlocked+0xc7/0x120 fs/namei.c:3004
       ovl_lookup_positive_unlocked fs/overlayfs/namei.c:210 [inline]
       ovl_lookup_single+0x214/0xfc0 fs/overlayfs/namei.c:240
       ovl_lookup_layer+0x3d4/0x480 fs/overlayfs/namei.c:333
       ovl_lookup+0x13f9/0x21a0 fs/overlayfs/namei.c:1156
       __lookup_slow+0x251/0x460 fs/namei.c:1817
       lookup_slow fs/namei.c:1834 [inline]
       walk_component+0x353/0x5b0 fs/namei.c:2138
       lookup_last fs/namei.c:2639 [inline]
       path_lookupat+0x142/0x6d0 fs/namei.c:2663
       filename_lookup+0x224/0x5f0 fs/namei.c:2692
       kern_path+0x35/0x50 fs/namei.c:2825
       lookup_bdev+0xd8/0x280 block/bdev.c:1205
       resume_store+0x1d6/0x460 kernel/power/hibernate.c:1272
       kobj_attr_store+0x55/0x80 lib/kobject.c:840
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
       kernfs_fop_write_iter+0x351/0x510 fs/kernfs/file.c:334
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x6c4/0x1150 fs/read_write.c:686
       ksys_write+0x12a/0x250 fs/read_write.c:738
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
       __do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
       do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

other info that might help us debug this:

Chain exists of:
  &ovl_i_mutex_dir_key[depth] --> &of->mutex --> &ovl_i_mutex_dir_key[depth]#2

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&ovl_i_mutex_dir_key[depth]#2);
                               lock(&of->mutex);
                               lock(&ovl_i_mutex_dir_key[depth]#2);
  rlock(&ovl_i_mutex_dir_key[depth]);

 *** DEADLOCK ***

5 locks held by syz.3.4164/22783:
 #0: ffff888051c28478 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2a2/0x370 fs/file.c:1213
 #1: ffff888024514428 (sb_writers#7){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:738
 #2: ffff8880276a4888 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x28f/0x510 fs/kernfs/file.c:325
 #3: ffff88801c3f3008 (kn->active#73){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x2b2/0x510 fs/kernfs/file.c:326
 #4: ffff88801273e3b0 (&ovl_i_mutex_dir_key[depth]#2){.+.+}-{4:4}, at: inode_lock_shared include/linux/fs.h:882 [inline]
 #4: ffff88801273e3b0 (&ovl_i_mutex_dir_key[depth]#2){.+.+}-{4:4}, at: lookup_slow fs/namei.c:1833 [inline]
 #4: ffff88801273e3b0 (&ovl_i_mutex_dir_key[depth]#2){.+.+}-{4:4}, at: walk_component+0x345/0x5b0 fs/namei.c:2138

stack backtrace:
CPU: 1 UID: 0 PID: 22783 Comm: syz.3.4164 Not tainted 6.16.0-rc1-syzkaller-00005-g488ef3560196 #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2046
 check_noncircular+0x14c/0x170 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain kernel/locking/lockdep.c:3911 [inline]
 __lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5240
 lock_acquire kernel/locking/lockdep.c:5871 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5828
 down_read+0x9b/0x480 kernel/locking/rwsem.c:1524
 inode_lock_shared include/linux/fs.h:882 [inline]
 lookup_slow fs/namei.c:1833 [inline]
 lookup_one_unlocked fs/namei.c:3016 [inline]
 lookup_one_unlocked+0xc7/0x120 fs/namei.c:3004
 ovl_lookup_positive_unlocked fs/overlayfs/namei.c:210 [inline]
 ovl_lookup_single+0x214/0xfc0 fs/overlayfs/namei.c:240
 ovl_lookup_layer+0x3d4/0x480 fs/overlayfs/namei.c:333
 ovl_lookup+0x13f9/0x21a0 fs/overlayfs/namei.c:1156
 __lookup_slow+0x251/0x460 fs/namei.c:1817
 lookup_slow fs/namei.c:1834 [inline]
 walk_component+0x353/0x5b0 fs/namei.c:2138
 lookup_last fs/namei.c:2639 [inline]
 path_lookupat+0x142/0x6d0 fs/namei.c:2663
 filename_lookup+0x224/0x5f0 fs/namei.c:2692
 kern_path+0x35/0x50 fs/namei.c:2825
 lookup_bdev+0xd8/0x280 block/bdev.c:1205
 resume_store+0x1d6/0x460 kernel/power/hibernate.c:1272
 kobj_attr_store+0x55/0x80 lib/kobject.c:840
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
 kernfs_fop_write_iter+0x351/0x510 fs/kernfs/file.c:334
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x6c4/0x1150 fs/read_write.c:686
 ksys_write+0x12a/0x250 fs/read_write.c:738
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
 do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf706e579
Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00
RSP: 002b:00000000f503d55c EFLAGS: 00000296 ORIG_RAX: 0000000000000004
RAX: ffffffffffffffda RBX: 0000000000000008 RCX: 0000000080000040
RDX: 0000000000000012 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000296 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
PM: Image not found (code -22)
----------------
Code disassembly (best guess), 2 bytes skipped:
   0:	10 06                	adc    %al,(%rsi)
   2:	03 74 b4 01          	add    0x1(%rsp,%rsi,4),%esi
   6:	10 07                	adc    %al,(%rdi)
   8:	03 74 b0 01          	add    0x1(%rax,%rsi,4),%esi
   c:	10 08                	adc    %cl,(%rax)
   e:	03 74 d8 01          	add    0x1(%rax,%rbx,8),%esi
  1e:	00 51 52             	add    %dl,0x52(%rcx)
  21:	55                   	push   %rbp
  22:	89 e5                	mov    %esp,%ebp
  24:	0f 34                	sysenter
  26:	cd 80                	int    $0x80
* 28:	5d                   	pop    %rbp <-- trapping instruction
  29:	5a                   	pop    %rdx
  2a:	59                   	pop    %rcx
  2b:	c3                   	ret
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	90                   	nop
  2f:	90                   	nop
  30:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi
  37:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/06/12 00:28 upstream 488ef3560196 98683f8f .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 possible deadlock in lookup_one_unlocked
* Struck through repros no longer work on HEAD.