syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.7.1572/23611 is trying to acquire lock:
ffff888065655db0 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb8/0xe20 fs/seq_file.c:183

but task is already holding lock:
ffff88803e781858 (&pipe->mutex){+.+.}-{4:4}, at: splice_file_to_pipe+0x40/0x6c0 fs/splice.c:1287

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&pipe->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:533 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:552
       iter_file_splice_write+0x1f3/0x10f0 fs/splice.c:682
       do_splice_from fs/splice.c:936 [inline]
       do_splice+0xef8/0x1940 fs/splice.c:1349
       __do_splice fs/splice.c:1431 [inline]
       __do_sys_splice fs/splice.c:1634 [inline]
       __se_sys_splice+0x353/0x490 fs/splice.c:1616
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (sb_writers#5){.+.+}-{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+0x4d/0x1c0 include/linux/fs/super.h:125
       mnt_want_write+0x41/0x90 fs/namespace.c:493
       ovl_setattr+0x2c9/0x580 fs/overlayfs/inode.c:75
       notify_change+0xc18/0xf60 fs/attr.c:556
       chmod_common+0x273/0x4a0 fs/open.c:639
       do_fchmodat+0x12d/0x230 fs/open.c:684
       __do_sys_fchmodat fs/open.c:703 [inline]
       __se_sys_fchmodat fs/open.c:700 [inline]
       __x64_sys_fchmodat+0x7d/0x90 fs/open.c:700
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&ovl_i_mutex_dir_key[depth]){++++}-{4:4}:
       down_read+0x97/0x200 kernel/locking/rwsem.c:1537
       inode_lock_shared include/linux/fs.h:1043 [inline]
       lookup_slow+0x46/0x70 fs/namei.c:1932
       walk_component fs/namei.c:2279 [inline]
       lookup_last fs/namei.c:2780 [inline]
       path_lookupat+0x3f5/0x8c0 fs/namei.c:2804
       filename_lookup+0x256/0x5d0 fs/namei.c:2833
       kern_path+0x3d/0x150 fs/namei.c:3040
       lookup_bdev+0xc8/0x290 block/bdev.c:1221
       resume_store+0x16f/0x4f0 kernel/power/hibernate.c:1306
       kernfs_fop_write_iter+0x3b0/0x540 fs/kernfs/file.c:352
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x629/0xba0 fs/read_write.c:688
       ksys_write+0x156/0x270 fs/read_write.c:740
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&of->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:533 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:552
       kernfs_seq_start+0x5c/0x420 fs/kernfs/file.c:172
       seq_read_iter+0x3f8/0xe20 fs/seq_file.c:226
       copy_splice_read+0x605/0xab0 fs/splice.c:362
       do_splice_read fs/splice.c:980 [inline]
       splice_direct_to_actor+0x483/0xc80 fs/splice.c:1084
       do_splice_direct_actor fs/splice.c:1202 [inline]
       do_splice_direct+0x19b/0x2a0 fs/splice.c:1228
       do_sendfile+0x547/0x7e0 fs/read_write.c:1372
       __do_sys_sendfile64 fs/read_write.c:1433 [inline]
       __se_sys_sendfile64+0x144/0x1a0 fs/read_write.c:1419
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&p->lock){+.+.}-{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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/rtmutex_api.c:533 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:552
       seq_read_iter+0xb8/0xe20 fs/seq_file.c:183
       proc_reg_read_iter+0x1bf/0x290 fs/proc/inode.c:299
       copy_splice_read+0x605/0xab0 fs/splice.c:362
       do_splice_read fs/splice.c:980 [inline]
       splice_file_to_pipe+0x452/0x6c0 fs/splice.c:1290
       do_sendfile+0x4ed/0x7e0 fs/read_write.c:1378
       __do_sys_sendfile64 fs/read_write.c:1433 [inline]
       __se_sys_sendfile64+0x144/0x1a0 fs/read_write.c:1419
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/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:
  &p->lock --> sb_writers#5 --> &pipe->mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&pipe->mutex);
                               lock(sb_writers#5);
                               lock(&pipe->mutex);
  lock(&p->lock);

 *** DEADLOCK ***

1 lock held by syz.7.1572/23611:
 #0: ffff88803e781858 (&pipe->mutex){+.+.}-{4:4}, at: splice_file_to_pipe+0x40/0x6c0 fs/splice.c:1287

stack backtrace:
CPU: 0 UID: 0 PID: 23611 Comm: syz.7.1572 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/rtmutex_api.c:533 [inline]
 mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:552
 seq_read_iter+0xb8/0xe20 fs/seq_file.c:183
 proc_reg_read_iter+0x1bf/0x290 fs/proc/inode.c:299
 copy_splice_read+0x605/0xab0 fs/splice.c:362
 do_splice_read fs/splice.c:980 [inline]
 splice_file_to_pipe+0x452/0x6c0 fs/splice.c:1290
 do_sendfile+0x4ed/0x7e0 fs/read_write.c:1378
 __do_sys_sendfile64 fs/read_write.c:1433 [inline]
 __se_sys_sendfile64+0x144/0x1a0 fs/read_write.c:1419
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f21df47c799
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:00007f21dd6b5028 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f21df6f6090 RCX: 00007f21df47c799
RDX: 0000000000000000 RSI: 0000000000000007 RDI: 0000000000000000
RBP: 00007f21df512c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000100004000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f21df6f6128 R14: 00007f21df6f6090 R15: 00007fff0149e4f8
 </TASK>