syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.906/9066 is trying to acquire lock:
ffff88805877c488 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x28f/0x570 fs/kernfs/file.c:343

but task is already holding lock:
ffff88807a2b2468 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock fs/pipe.c:91 [inline]
ffff88807a2b2468 (&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/0x1b10 kernel/locking/mutex.c:776
       pipe_lock fs/pipe.c:91 [inline]
       pipe_lock+0x64/0x80 fs/pipe.c:88
       iter_file_splice_write+0x1ea/0x12b0 fs/splice.c:683
       backing_file_splice_write+0x27f/0x880 fs/backing-file.c:314
       ovl_splice_write+0x38d/0x6c0 fs/overlayfs/file.c:432
       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

-> #2 (sb_writers#6){.+.+}-{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/super.h:19 [inline]
       sb_start_write include/linux/fs/super.h:125 [inline]
       mnt_want_write+0x6f/0x450 fs/namespace.c:499
       ovl_setattr+0x1c1/0x5a0 fs/overlayfs/inode.c:75
       notify_change+0x6d2/0x1290 fs/attr.c:546
       chmod_common+0x224/0x470 fs/open.c:647
       do_fchmodat fs/open.c:694 [inline]
       __do_sys_fchmodat fs/open.c:713 [inline]
       __se_sys_fchmodat fs/open.c:710 [inline]
       __x64_sys_fchmodat+0x12b/0x1f0 fs/open.c:710
       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 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}:
       down_read+0x9b/0x460 kernel/locking/rwsem.c:1537
       inode_lock_shared include/linux/fs.h:1042 [inline]
       lookup_slow+0x42/0x70 fs/namei.c:1874
       walk_component fs/namei.c:2221 [inline]
       lookup_last fs/namei.c:2722 [inline]
       path_lookupat+0x5e9/0xc40 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+0x1d6/0x460 kernel/power/hibernate.c:1302
       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+0x1542/0x22f0 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/0x1b10 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 --> sb_writers#6 --> &pipe->mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&pipe->mutex);
                               lock(sb_writers#6);
                               lock(&pipe->mutex);
  lock(&of->mutex);

 *** DEADLOCK ***

2 locks held by syz.2.906/9066:
 #0: ffff888035f94420 (sb_writers#8){.+.+}-{0:0}, at: __do_splice+0x32a/0x360 fs/splice.c:1433
 #1: ffff88807a2b2468 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock fs/pipe.c:91 [inline]
 #1: ffff88807a2b2468 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock+0x64/0x80 fs/pipe.c:88

stack backtrace:
CPU: 1 UID: 0 PID: 9066 Comm: syz.2.906 Not tainted syzkaller #0 PREEMPT(full) 
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+0x2db/0x410 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+0x1542/0x22f0 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/0x1b10 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: 0033:0x7ff05818f749
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:00007ff058f57038 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007ff0583e6090 RCX: 00007ff05818f749
RDX: 0000000000000007 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007ff058213f91 R08: 000000000000bfd1 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff0583e6128 R14: 00007ff0583e6090 R15: 00007ffd48579a58
 </TASK>