syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.4.2250/14442 is trying to acquire lock:
ffff888056517088 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x28f/0x570 fs/kernfs/file.c:343

but task is already holding lock:
ffff88807ad64868 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock fs/pipe.c:91 [inline]
ffff88807ad64868 (&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:

-> #2 (&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
       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 (&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

-> #0 (&of->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+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
       kernfs_fop_write_iter+0x28f/0x570 fs/kernfs/file.c:343
       iter_file_splice_write+0xa24/0x12b0 fs/splice.c:738
       do_splice_from fs/splice.c:938 [inline]
       do_splice+0x1478/0x1fc0 fs/splice.c:1351
       __do_splice+0x32a/0x360 fs/splice.c:1433
       __do_sys_splice fs/splice.c:1636 [inline]
       __se_sys_splice fs/splice.c:1618 [inline]
       __x64_sys_splice+0x187/0x250 fs/splice.c:1618
       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:
  &of->mutex --> &sbi->pipe_mutex --> &pipe->mutex

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

2 locks held by syz.4.2250/14442:
 #0: ffff888035ad6420 (sb_writers#8){.+.+}-{0:0}, at: __do_splice+0x32a/0x360 fs/splice.c:1433
 #1: ffff88807ad64868 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock fs/pipe.c:91 [inline]
 #1: ffff88807ad64868 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock+0x64/0x80 fs/pipe.c:88

stack backtrace:
CPU: 0 UID: 0 PID: 14442 Comm: syz.4.2250 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
 kernfs_fop_write_iter+0x28f/0x570 fs/kernfs/file.c:343
 iter_file_splice_write+0xa24/0x12b0 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 do_splice+0x1478/0x1fc0 fs/splice.c:1351
 __do_splice+0x32a/0x360 fs/splice.c:1433
 __do_sys_splice fs/splice.c:1636 [inline]
 __se_sys_splice fs/splice.c:1618 [inline]
 __x64_sys_splice+0x187/0x250 fs/splice.c:1618
 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: 0033:0x7ffae1b8f749
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:00007ffae2af2038 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007ffae1de6090 RCX: 00007ffae1b8f749
RDX: 0000000000000008 RSI: 0000000000000000 RDI: 0000000000000006
RBP: 00007ffae1c13f91 R08: 000000000000bfd1 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffae1de6128 R14: 00007ffae1de6090 R15: 00007ffd3ce979c8
 </TASK>