syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.5.6367/31726 is trying to acquire lock:
ffff88802a721668 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xe1/0x12d0 fs/seq_file.c:182

but task is already holding lock:
ffff8880790db068 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock fs/pipe.c:91 [inline]
ffff8880790db068 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock+0x64/0x80 fs/pipe.c:88

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&pipe->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1aa/0x1ca0 kernel/locking/mutex.c:776
       anon_pipe_write+0x15d/0x1bd0 fs/pipe.c:458
       __kernel_write_iter+0x720/0xb10 fs/read_write.c:619
       __kernel_write+0xf5/0x140 fs/read_write.c:639
       autofs_write fs/autofs/waitq.c:57 [inline]
       autofs_notify_daemon+0x4db/0xd60 fs/autofs/waitq.c:164
       autofs_wait+0x10f3/0x1ac0 fs/autofs/waitq.c:426
       autofs_mount_wait+0x132/0x3c0 fs/autofs/root.c:255
       autofs_d_automount+0x4b2/0x960 fs/autofs/root.c:409
       follow_automount fs/namei.c:1499 [inline]
       __traverse_mounts+0x1b9/0x830 fs/namei.c:1552
       traverse_mounts fs/namei.c:1581 [inline]
       handle_mounts fs/namei.c:1686 [inline]
       step_into_slowpath+0x772/0xf50 fs/namei.c:2043
       step_into fs/namei.c:2091 [inline]
       walk_component fs/namei.c:2227 [inline]
       lookup_last fs/namei.c:2722 [inline]
       path_lookupat+0x627/0xc40 fs/namei.c:2746
       filename_lookup+0x224/0x5f0 fs/namei.c:2775
       user_path_at+0x3a/0x60 fs/namei.c:3567
       do_mount fs/namespace.c:4032 [inline]
       __do_sys_mount fs/namespace.c:4224 [inline]
       __se_sys_mount fs/namespace.c:4201 [inline]
       __x64_sys_mount+0x1fb/0x310 fs/namespace.c:4201
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&sbi->pipe_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1aa/0x1ca0 kernel/locking/mutex.c:776
       autofs_write fs/autofs/waitq.c:55 [inline]
       autofs_notify_daemon+0x4a6/0xd60 fs/autofs/waitq.c:164
       autofs_wait+0x10f3/0x1ac0 fs/autofs/waitq.c:426
       autofs_mount_wait+0x132/0x3c0 fs/autofs/root.c:255
       autofs_d_automount+0x4b2/0x960 fs/autofs/root.c:409
       follow_automount fs/namei.c:1499 [inline]
       __traverse_mounts+0x1b9/0x830 fs/namei.c:1552
       traverse_mounts fs/namei.c:1581 [inline]
       handle_mounts fs/namei.c:1686 [inline]
       step_into_slowpath+0x772/0xf50 fs/namei.c:2043
       step_into fs/namei.c:2091 [inline]
       walk_component fs/namei.c:2227 [inline]
       lookup_last fs/namei.c:2722 [inline]
       path_lookupat+0x627/0xc40 fs/namei.c:2746
       filename_lookup+0x224/0x5f0 fs/namei.c:2775
       kern_path+0x35/0x50 fs/namei.c:2987
       lookup_bdev+0xd8/0x280 block/bdev.c:1222
       resume_store+0x1d6/0x490 kernel/power/hibernate.c:1306
       kobj_attr_store+0x58/0x80 lib/kobject.c:840
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
       kernfs_fop_write_iter+0x3af/0x570 fs/kernfs/file.c:352
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x7d3/0x11d0 fs/read_write.c:686
       ksys_write+0x12a/0x250 fs/read_write.c:738
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&of->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1aa/0x1ca0 kernel/locking/mutex.c:776
       kernfs_seq_start+0x4f/0x2a0 fs/kernfs/file.c:172
       traverse.part.0.constprop.0+0xaf/0x650 fs/seq_file.c:106
       traverse fs/seq_file.c:98 [inline]
       seq_read_iter+0x93c/0x12d0 fs/seq_file.c:195
       kernfs_fop_read_iter+0x46c/0x610 fs/kernfs/file.c:297
       do_iter_readv_writev+0x743/0x9e0 fs/read_write.c:825
       vfs_readv+0x4cb/0x8b0 fs/read_write.c:1018
       do_preadv+0x1a6/0x270 fs/read_write.c:1132
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&p->lock){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x1669/0x2890 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1aa/0x1ca0 kernel/locking/mutex.c:776
       seq_read_iter+0xe1/0x12d0 fs/seq_file.c:182
       kernfs_fop_read_iter+0x46c/0x610 fs/kernfs/file.c:297
       copy_splice_read+0x618/0xc20 fs/splice.c:363
       do_splice_read fs/splice.c:982 [inline]
       do_splice_read+0x285/0x370 fs/splice.c:956
       splice_file_to_pipe+0x109/0x120 fs/splice.c:1292
       do_sendfile+0x400/0xe50 fs/read_write.c:1376
       __do_sys_sendfile64 fs/read_write.c:1431 [inline]
       __se_sys_sendfile64 fs/read_write.c:1417 [inline]
       __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1417
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xf80 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:
  &p->lock --> &sbi->pipe_mutex --> &pipe->mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&pipe->mutex);
                               lock(&sbi->pipe_mutex);
                               lock(&pipe->mutex);
  lock(&p->lock);

 *** DEADLOCK ***

1 lock held by syz.5.6367/31726:
 #0: ffff8880790db068 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock fs/pipe.c:91 [inline]
 #0: ffff8880790db068 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock+0x64/0x80 fs/pipe.c:88

stack backtrace:
CPU: 1 UID: 0 PID: 31726 Comm: syz.5.6367 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x340 kernel/locking/lockdep.c:2043
 check_noncircular+0x146/0x160 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 kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x1669/0x2890 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:614 [inline]
 __mutex_lock+0x1aa/0x1ca0 kernel/locking/mutex.c:776
 seq_read_iter+0xe1/0x12d0 fs/seq_file.c:182
 kernfs_fop_read_iter+0x46c/0x610 fs/kernfs/file.c:297
 copy_splice_read+0x618/0xc20 fs/splice.c:363
 do_splice_read fs/splice.c:982 [inline]
 do_splice_read+0x285/0x370 fs/splice.c:956
 splice_file_to_pipe+0x109/0x120 fs/splice.c:1292
 do_sendfile+0x400/0xe50 fs/read_write.c:1376
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64 fs/read_write.c:1417 [inline]
 __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1417
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7b0cf8f749
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:00007f7b0de39038 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f7b0d1e5fa0 RCX: 00007f7b0cf8f749
RDX: 0000000000000000 RSI: 0000000000000007 RDI: 0000000000000000
RBP: 00007f7b0d013f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7b0d1e6038 R14: 00007f7b0d1e5fa0 R15: 00007ffe92377088
 </TASK>