syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.4.3310/18534 is trying to acquire lock:
ffff888033580148 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_write fs/autofs/waitq.c:55 [inline]
ffff888033580148 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_notify_daemon+0x4f8/0xd90 fs/autofs/waitq.c:164

but task is already holding lock:
ffff8880437f1488 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:343

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&of->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
       kernfs_seq_start+0x4f/0x2a0 fs/kernfs/file.c:172
       seq_read_iter+0x2c1/0x1270 fs/seq_file.c:226
       kernfs_fop_read_iter+0x46c/0x610 fs/kernfs/file.c:297
       copy_splice_read+0x4ba/0xb90 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+0x82/0x120 fs/splice.c:1292
       do_sendfile+0x366/0xe20 fs/read_write.c:1378
       __do_sys_sendfile64 fs/read_write.c:1433 [inline]
       __se_sys_sendfile64 fs/read_write.c:1419 [inline]
       __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1419
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&p->lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
       seq_read_iter+0xe1/0x1270 fs/seq_file.c:183
       kernfs_fop_read_iter+0x46c/0x610 fs/kernfs/file.c:297
       copy_splice_read+0x4ba/0xb90 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+0x82/0x120 fs/splice.c:1292
       do_sendfile+0x366/0xe20 fs/read_write.c:1378
       __do_sys_sendfile64 fs/read_write.c:1433 [inline]
       __se_sys_sendfile64 fs/read_write.c:1419 [inline]
       __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1419
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&pipe->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
       anon_pipe_write+0x163/0x1d40 fs/pipe.c:458
       __kernel_write_iter+0x6b2/0x920 fs/read_write.c:621
       __kernel_write+0xf6/0x140 fs/read_write.c:641
       autofs_write fs/autofs/waitq.c:57 [inline]
       autofs_notify_daemon+0x50d/0xd90 fs/autofs/waitq.c:164
       autofs_wait+0x10fd/0x1b50 fs/autofs/waitq.c:426
       autofs_mount_wait+0x132/0x3b0 fs/autofs/root.c:255
       autofs_d_automount+0x490/0x950 fs/autofs/root.c:409
       follow_automount fs/namei.c:1560 [inline]
       __traverse_mounts+0x1b9/0x8a0 fs/namei.c:1613
       traverse_mounts fs/namei.c:1642 [inline]
       handle_mounts fs/namei.c:1744 [inline]
       step_into_slowpath+0xb7e/0xf90 fs/namei.c:2101
       step_into fs/namei.c:2149 [inline]
       walk_component fs/namei.c:2285 [inline]
       lookup_last fs/namei.c:2780 [inline]
       path_lookupat+0x58b/0xc40 fs/namei.c:2804
       filename_lookup+0x202/0x590 fs/namei.c:2833
       user_path_at+0x3c/0x60 fs/namei.c:3612
       do_mount fs/namespace.c:4156 [inline]
       __do_sys_mount fs/namespace.c:4348 [inline]
       __se_sys_mount fs/namespace.c:4325 [inline]
       __x64_sys_mount+0x1fb/0x310 fs/namespace.c:4325
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&sbi->pipe_mutex){+.+.}-{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+0x14b8/0x2630 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
       autofs_write fs/autofs/waitq.c:55 [inline]
       autofs_notify_daemon+0x4f8/0xd90 fs/autofs/waitq.c:164
       autofs_wait+0x10fd/0x1b50 fs/autofs/waitq.c:426
       autofs_mount_wait+0x132/0x3b0 fs/autofs/root.c:255
       autofs_d_automount+0x490/0x950 fs/autofs/root.c:409
       follow_automount fs/namei.c:1560 [inline]
       __traverse_mounts+0x1b9/0x8a0 fs/namei.c:1613
       traverse_mounts fs/namei.c:1642 [inline]
       handle_mounts fs/namei.c:1744 [inline]
       step_into_slowpath+0xb7e/0xf90 fs/namei.c:2101
       step_into fs/namei.c:2149 [inline]
       walk_component fs/namei.c:2285 [inline]
       lookup_last fs/namei.c:2780 [inline]
       path_lookupat+0x58b/0xc40 fs/namei.c:2804
       filename_lookup+0x202/0x590 fs/namei.c:2833
       kern_path+0x37/0x50 fs/namei.c:3040
       lookup_bdev+0xd8/0x280 block/bdev.c:1221
       resume_store+0x1d6/0x460 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+0x3e0/0x5f0 fs/kernfs/file.c:352
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x6ac/0x1070 fs/read_write.c:688
       ksys_write+0x12a/0x250 fs/read_write.c:740
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x106/0xf80 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:
  &sbi->pipe_mutex --> &p->lock --> &of->mutex

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

4 locks held by syz.4.3310/18534:
 #0: ffff88807c0f07f8 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2aa/0x380 fs/file.c:1261
 #1: ffff888036cd8420 (sb_writers#8){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:740
 #2: ffff8880437f1488 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x2c2/0x5f0 fs/kernfs/file.c:343
 #3: ffff88801fe885a8 (kn->active#62){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:80 [inline]
 #3: ffff88801fe885a8 (kn->active#62){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x332/0x5f0 fs/kernfs/file.c:344

stack backtrace:
CPU: 0 UID: 0 PID: 18534 Comm: syz.4.3310 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_circular_bug.cold+0x178/0x1c7 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+0x14b8/0x2630 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x1cf/0x380 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:614 [inline]
 __mutex_lock+0x1a2/0x1b90 kernel/locking/mutex.c:776
 autofs_write fs/autofs/waitq.c:55 [inline]
 autofs_notify_daemon+0x4f8/0xd90 fs/autofs/waitq.c:164
 autofs_wait+0x10fd/0x1b50 fs/autofs/waitq.c:426
 autofs_mount_wait+0x132/0x3b0 fs/autofs/root.c:255
 autofs_d_automount+0x490/0x950 fs/autofs/root.c:409
 follow_automount fs/namei.c:1560 [inline]
 __traverse_mounts+0x1b9/0x8a0 fs/namei.c:1613
 traverse_mounts fs/namei.c:1642 [inline]
 handle_mounts fs/namei.c:1744 [inline]
 step_into_slowpath+0xb7e/0xf90 fs/namei.c:2101
 step_into fs/namei.c:2149 [inline]
 walk_component fs/namei.c:2285 [inline]
 lookup_last fs/namei.c:2780 [inline]
 path_lookupat+0x58b/0xc40 fs/namei.c:2804
 filename_lookup+0x202/0x590 fs/namei.c:2833
 kern_path+0x37/0x50 fs/namei.c:3040
 lookup_bdev+0xd8/0x280 block/bdev.c:1221
 resume_store+0x1d6/0x460 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+0x3e0/0x5f0 fs/kernfs/file.c:352
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6ac/0x1070 fs/read_write.c:688
 ksys_write+0x12a/0x250 fs/read_write.c:740
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f158519c629
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:00007f1586052028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f1585416090 RCX: 00007f158519c629
RDX: 0000000000000012 RSI: 00002000000000c0 RDI: 0000000000000007
RBP: 00007f1585232b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1585416128 R14: 00007f1585416090 R15: 00007ffeb0422168
 </TASK>
PM: Image not found (code -6)