syzbot

======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc2-syzkaller-00269-g11313e2f7812 #0 Not tainted
------------------------------------------------------
syz.1.5307/23843 is trying to acquire lock:
ffff888031fec9e0 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xb7/0xe10 fs/seq_file.c:182

but task is already holding lock:
ffff888032d2dc68 (&pipe->mutex){+.+.}-{4:4}, at: splice_file_to_pipe+0x2e/0x440 fs/splice.c:1286

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&pipe->mutex){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       iter_file_splice_write+0x1e6/0x1000 fs/splice.c:683
       do_splice_from fs/splice.c:935 [inline]
       do_splice+0xc76/0x1660 fs/splice.c:1348
       __do_splice fs/splice.c:1430 [inline]
       __do_sys_splice fs/splice.c:1633 [inline]
       __se_sys_splice+0x2e1/0x460 fs/splice.c:1615
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (sb_writers#5){.+.+}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       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:1795 [inline]
       sb_start_write+0x4d/0x1c0 include/linux/fs.h:1931
       mnt_want_write+0x41/0x90 fs/namespace.c:557
       ovl_create_object+0xfc/0x310 fs/overlayfs/dir.c:628
       lookup_open fs/namei.c:3717 [inline]
       open_last_lookups fs/namei.c:3816 [inline]
       path_openat+0x14f1/0x3830 fs/namei.c:4052
       do_filp_open+0x1fa/0x410 fs/namei.c:4082
       do_sys_openat2+0x121/0x1c0 fs/open.c:1437
       do_sys_open fs/open.c:1452 [inline]
       __do_sys_open fs/open.c:1460 [inline]
       __se_sys_open fs/open.c:1456 [inline]
       __x64_sys_open+0x11e/0x150 fs/open.c:1456
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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+0x120/0x360 kernel/locking/lockdep.c:5871
       down_read+0x46/0x2e0 kernel/locking/rwsem.c:1524
       inode_lock_shared include/linux/fs.h:884 [inline]
       lookup_slow+0x46/0x70 fs/namei.c:1833
       walk_component+0x2d2/0x400 fs/namei.c:2138
       lookup_last fs/namei.c:2639 [inline]
       path_lookupat+0x163/0x430 fs/namei.c:2663
       filename_lookup+0x212/0x570 fs/namei.c:2692
       kern_path+0x35/0x50 fs/namei.c:2825
       lookup_bdev+0xc0/0x280 block/bdev.c:1205
       resume_store+0x169/0x460 kernel/power/hibernate.c:1272
       kernfs_fop_write_iter+0x375/0x4f0 fs/kernfs/file.c:334
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x548/0xa90 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/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&of->mutex){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       kernfs_seq_start+0x55/0x3c0 fs/kernfs/file.c:154
       traverse+0x15f/0x570 fs/seq_file.c:106
       seq_read_iter+0xcfe/0xe10 fs/seq_file.c:195
       new_sync_read fs/read_write.c:491 [inline]
       vfs_read+0x4cd/0x980 fs/read_write.c:572
       ksys_pread64 fs/read_write.c:763 [inline]
       __do_sys_pread64 fs/read_write.c:771 [inline]
       __se_sys_pread64 fs/read_write.c:768 [inline]
       __x64_sys_pread64+0x193/0x220 fs/read_write.c:768
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       seq_read_iter+0xb7/0xe10 fs/seq_file.c:182
       proc_reg_read_iter+0x1b7/0x280 fs/proc/inode.c:299
       copy_splice_read+0x54f/0x9b0 fs/splice.c:363
       do_splice_read fs/splice.c:979 [inline]
       splice_file_to_pipe+0x270/0x440 fs/splice.c:1289
       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/0x3b0 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.1.5307/23843:
 #0: ffff888032d2dc68 (&pipe->mutex){+.+.}-{4:4}, at: splice_file_to_pipe+0x2e/0x440 fs/splice.c:1286

stack backtrace:
CPU: 1 UID: 0 PID: 23843 Comm: syz.1.5307 Not tainted 6.16.0-rc2-syzkaller-00269-g11313e2f7812 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 __mutex_lock_common kernel/locking/mutex.c:602 [inline]
 __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
 seq_read_iter+0xb7/0xe10 fs/seq_file.c:182
 proc_reg_read_iter+0x1b7/0x280 fs/proc/inode.c:299
 copy_splice_read+0x54f/0x9b0 fs/splice.c:363
 do_splice_read fs/splice.c:979 [inline]
 splice_file_to_pipe+0x270/0x440 fs/splice.c:1289
 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/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f097078e929
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:00007f097165c038 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f09709b5fa0 RCX: 00007f097078e929
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000001
RBP: 00007f0970810b39 R08: 0000000000000000 R09: 0000000000000000
R10: 4000000000010042 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f09709b5fa0 R15: 00007ffc5b92ad08
 </TASK>