syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.1.5524/28942 is trying to acquire lock:
ffff88807a66cab8 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xe1/0x1270 fs/seq_file.c:183

but task is already holding lock:
ffff888056077060 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock fs/pipe.c:91 [inline]
ffff888056077060 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock+0x69/0x80 fs/pipe.c:88

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&pipe->mutex){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       pipe_lock fs/pipe.c:91 [inline]
       pipe_lock+0x69/0x80 fs/pipe.c:88
       iter_file_splice_write+0x1fd/0x10b0 fs/splice.c:682
       do_splice_from fs/splice.c:936 [inline]
       do_splice+0x109c/0x1f90 fs/splice.c:1349
       __do_splice+0x33b/0x370 fs/splice.c:1431
       __do_sys_splice fs/splice.c:1634 [inline]
       __se_sys_splice fs/splice.c:1616 [inline]
       __x64_sys_splice+0x187/0x250 fs/splice.c:1616
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (sb_writers#6){.+.+}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       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/0x410 fs/namespace.c:494
       ovl_create_object+0x12b/0x3b0 fs/overlayfs/dir.c:706
       lookup_open fs/namei.c:4508 [inline]
       open_last_lookups fs/namei.c:4608 [inline]
       path_openat+0x341f/0x4280 fs/namei.c:4860
       do_file_open+0x20e/0x430 fs/namei.c:4892
       do_sys_openat2+0x10f/0x1e0 fs/open.c:1368
       do_sys_open fs/open.c:1374 [inline]
       __do_sys_openat fs/open.c:1390 [inline]
       __se_sys_openat fs/open.c:1385 [inline]
       __x64_sys_openat+0x12d/0x210 fs/open.c:1385
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       down_read+0x99/0x4c0 kernel/locking/rwsem.c:1574
       inode_lock_shared include/linux/fs.h:1039 [inline]
       lookup_slow+0x42/0x70 fs/namei.c:1935
       walk_component fs/namei.c:2282 [inline]
       lookup_last fs/namei.c:2789 [inline]
       path_lookupat+0x5e8/0xc40 fs/namei.c:2813
       filename_lookup+0x202/0x590 fs/namei.c:2842
       kern_path+0x37/0x50 fs/namei.c:3036
       lookup_bdev+0xd8/0x280 block/bdev.c:1208
       resume_store+0x1d6/0x460 kernel/power/hibernate.c:1278
       kobj_attr_store+0x58/0x80 lib/kobject.c:840
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
       kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
       iter_file_splice_write+0x830/0x10b0 fs/splice.c:736
       do_splice_from fs/splice.c:936 [inline]
       direct_splice_actor+0x192/0x690 fs/splice.c:1159
       splice_direct_to_actor+0x345/0xa30 fs/splice.c:1103
       do_splice_direct_actor fs/splice.c:1202 [inline]
       do_splice_direct+0x174/0x240 fs/splice.c:1228
       do_sendfile+0xadc/0xe20 fs/read_write.c:1371
       __do_sys_sendfile64 fs/read_write.c:1432 [inline]
       __se_sys_sendfile64 fs/read_write.c:1418 [inline]
       __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1418
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&of->mutex){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       kernfs_seq_start+0x4f/0x2a0 fs/kernfs/file.c:165
       traverse.part.0.constprop.0+0xaf/0x650 fs/seq_file.c:107
       traverse fs/seq_file.c:99 [inline]
       seq_read_iter+0x93f/0x1270 fs/seq_file.c:196
       kernfs_fop_read_iter+0x46c/0x610 fs/kernfs/file.c:290
       lo_rw_aio.isra.0+0x70a/0xdf0 drivers/block/loop.c:400
       do_req_filebacked drivers/block/loop.c:431 [inline]
       loop_handle_cmd drivers/block/loop.c:1921 [inline]
       loop_process_work+0x86c/0x11c0 drivers/block/loop.c:1956
       process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
       process_scheduled_works kernel/workqueue.c:3405 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
       kthread+0x370/0x450 kernel/kthread.c:436
       ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (&p->lock){+.+.}-{4:4}:
       check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       seq_read_iter+0xe1/0x1270 fs/seq_file.c:183
       kernfs_fop_read_iter+0x46c/0x610 fs/kernfs/file.c:290
       copy_splice_read+0x4ba/0xbb0 fs/splice.c:362
       do_splice_read fs/splice.c:980 [inline]
       do_splice_read+0x285/0x370 fs/splice.c:954
       splice_file_to_pipe+0x82/0x120 fs/splice.c:1290
       do_sendfile+0x366/0xe20 fs/read_write.c:1377
       __do_sys_sendfile64 fs/read_write.c:1432 [inline]
       __se_sys_sendfile64 fs/read_write.c:1418 [inline]
       __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1418
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x115/0x870 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 --> sb_writers#6 --> &pipe->mutex

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz.1.5524/28942:
 #0: ffff888056077060 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock fs/pipe.c:91 [inline]
 #0: ffff888056077060 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock+0x69/0x80 fs/pipe.c:88

stack backtrace:
CPU: 1 UID: 0 PID: 28942 Comm: syz.1.5524 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/10/2026
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+0xeb/0xe60 kernel/locking/lockdep.c:3165
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
 seq_read_iter+0xe1/0x1270 fs/seq_file.c:183
 kernfs_fop_read_iter+0x46c/0x610 fs/kernfs/file.c:290
 copy_splice_read+0x4ba/0xbb0 fs/splice.c:362
 do_splice_read fs/splice.c:980 [inline]
 do_splice_read+0x285/0x370 fs/splice.c:954
 splice_file_to_pipe+0x82/0x120 fs/splice.c:1290
 do_sendfile+0x366/0xe20 fs/read_write.c:1377
 __do_sys_sendfile64 fs/read_write.c:1432 [inline]
 __se_sys_sendfile64 fs/read_write.c:1418 [inline]
 __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1418
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f618539de59
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:00007f61862e9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f6185625fa0 RCX: 00007f618539de59
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000000
RBP: 00007f6185433e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6185626038 R14: 00007f6185625fa0 R15: 00007ffcf29971c8
 </TASK>