syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.3313/20789 is trying to acquire lock:
ffff888068a74468 (&pipe->mutex){+.+.}-{4:4}, at: iter_file_splice_write+0x1e0/0x10e0 fs/splice.c:683

but task is already holding lock:
ffff88802f694420 (sb_writers#5){.+.+}-{0:0}, at: do_splice+0xbff/0x1660 fs/splice.c:1350

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (sb_writers#5){.+.+}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       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:1916 [inline]
       sb_start_write+0x4d/0x1c0 include/linux/fs.h:2052
       mnt_want_write+0x41/0x90 fs/namespace.c:508
       ovl_create_object+0xfc/0x310 fs/overlayfs/dir.c:678
       lookup_open fs/namei.c:3796 [inline]
       open_last_lookups fs/namei.c:3895 [inline]
       path_openat+0x14f4/0x3830 fs/namei.c:4131
       do_filp_open+0x1fa/0x410 fs/namei.c:4161
       do_sys_openat2+0x121/0x1c0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_sys_openat fs/open.c:1468 [inline]
       __se_sys_openat fs/open.c:1463 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1463
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&ovl_i_mutex_dir_key[depth]#2){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       down_read+0x46/0x2e0 kernel/locking/rwsem.c:1537
       inode_lock_shared include/linux/fs.h:995 [inline]
       lookup_slow+0x46/0x70 fs/namei.c:1832
       walk_component+0x2d2/0x400 fs/namei.c:2151
       lookup_last fs/namei.c:2652 [inline]
       path_lookupat+0x163/0x430 fs/namei.c:2676
       filename_lookup+0x212/0x570 fs/namei.c:2705
       kern_path+0x35/0x50 fs/namei.c:2863
       lookup_bdev+0xc0/0x280 block/bdev.c:1205
       resume_store+0x169/0x460 kernel/power/hibernate.c:1309
       kernfs_fop_write_iter+0x3af/0x540 fs/kernfs/file.c:352
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x5c9/0xb30 fs/read_write.c:686
       ksys_write+0x145/0x250 fs/read_write.c:738
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&of->mutex){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
       kernfs_seq_start+0x5c/0x420 fs/kernfs/file.c:172
       traverse+0x164/0x580 fs/seq_file.c:106
       seq_read_iter+0xd08/0xe20 fs/seq_file.c:195
       do_iter_readv_writev+0x623/0x8c0 fs/read_write.c:-1
       vfs_readv+0x253/0x850 fs/read_write.c:1018
       do_preadv fs/read_write.c:1132 [inline]
       __do_sys_preadv fs/read_write.c:1179 [inline]
       __se_sys_preadv fs/read_write.c:1174 [inline]
       __x64_sys_preadv+0x197/0x2a0 fs/read_write.c:1174
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&p->lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
       seq_read_iter+0xb7/0xe20 fs/seq_file.c:182
       proc_reg_read_iter+0x1b7/0x280 fs/proc/inode.c:299
       copy_splice_read+0x5d4/0xa50 fs/splice.c:363
       do_splice_read fs/splice.c:982 [inline]
       splice_file_to_pipe+0x273/0x440 fs/splice.c:1292
       do_sendfile+0x475/0x7e0 fs/read_write.c:1376
       __do_sys_sendfile64 fs/read_write.c:1431 [inline]
       __se_sys_sendfile64+0x13e/0x190 fs/read_write.c:1417
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&pipe->mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
       iter_file_splice_write+0x1e0/0x10e0 fs/splice.c:683
       do_splice_from fs/splice.c:938 [inline]
       do_splice+0xc79/0x1660 fs/splice.c:1351
       __do_splice fs/splice.c:1433 [inline]
       __do_sys_splice fs/splice.c:1636 [inline]
       __se_sys_splice+0x2e1/0x460 fs/splice.c:1618
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 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:
  &pipe->mutex --> &ovl_i_mutex_dir_key[depth]#2 --> sb_writers#5

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(sb_writers#5);
                               lock(&ovl_i_mutex_dir_key[depth]#2);
                               lock(sb_writers#5);
  lock(&pipe->mutex);

 *** DEADLOCK ***

1 lock held by syz.1.3313/20789:
 #0: ffff88802f694420 (sb_writers#5){.+.+}-{0:0}, at: do_splice+0xbff/0x1660 fs/splice.c:1350

stack backtrace:
CPU: 1 UID: 0 PID: 20789 Comm: syz.1.3313 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:598 [inline]
 __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
 iter_file_splice_write+0x1e0/0x10e0 fs/splice.c:683
 do_splice_from fs/splice.c:938 [inline]
 do_splice+0xc79/0x1660 fs/splice.c:1351
 __do_splice fs/splice.c:1433 [inline]
 __do_sys_splice fs/splice.c:1636 [inline]
 __se_sys_splice+0x2e1/0x460 fs/splice.c:1618
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc9d378efc9
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:00007fc9d461b038 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007fc9d39e5fa0 RCX: 00007fc9d378efc9
RDX: 0000000000000007 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00007fc9d3811f91 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc9d39e6038 R14: 00007fc9d39e5fa0 R15: 00007fffd3ace9d8
 </TASK>