syzbot

9pnet_fd: Insufficient options for proto=fd
======================================================
WARNING: possible circular locking dependency detected
6.16.0-syzkaller-11105-ga6923c06a3b2 #0 Not tainted
------------------------------------------------------
syz.6.2097/14575 is trying to acquire lock:
ffff88804e4b4868 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock fs/pipe.c:91 [inline]
ffff88804e4b4868 (&pipe->mutex){+.+.}-{4:4}, at: pipe_lock+0x64/0x80 fs/pipe.c:88

but task is already holding lock:
ffff888076a0a428 (sb_writers#6){.+.+}-{0:0}, at: __do_splice+0x32a/0x360 fs/splice.c:1430

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (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.h:1798 [inline]
       sb_start_write include/linux/fs.h:1934 [inline]
       mnt_want_write+0x6f/0x450 fs/namespace.c:557
       ovl_create_object+0x12c/0x300 fs/overlayfs/dir.c:651
       lookup_open.isra.0+0x11d0/0x1580 fs/namei.c:3708
       open_last_lookups fs/namei.c:3807 [inline]
       path_openat+0x893/0x2cb0 fs/namei.c:4043
       do_filp_open+0x20b/0x470 fs/namei.c:4073
       do_sys_openat2+0x11b/0x1d0 fs/open.c:1435
       do_sys_open fs/open.c:1450 [inline]
       __do_sys_openat fs/open.c:1466 [inline]
       __se_sys_openat fs/open.c:1461 [inline]
       __x64_sys_openat+0x174/0x210 fs/open.c:1461
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&ovl_i_mutex_dir_key[depth]#2){++++}-{4:4}:
       down_read+0x9b/0x480 kernel/locking/rwsem.c:1522
       inode_lock_shared include/linux/fs.h:884 [inline]
       lookup_slow fs/namei.c:1824 [inline]
       walk_component+0x345/0x5b0 fs/namei.c:2129
       lookup_last fs/namei.c:2630 [inline]
       path_lookupat+0x142/0x6d0 fs/namei.c:2654
       filename_lookup+0x224/0x5f0 fs/namei.c:2683
       kern_path+0x35/0x50 fs/namei.c:2816
       lookup_bdev+0xd8/0x280 block/bdev.c:1205
       resume_store+0x1d6/0x460 kernel/power/hibernate.c:1295
       kobj_attr_store+0x55/0x80 lib/kobject.c:840
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
       kernfs_fop_write_iter+0x354/0x510 fs/kernfs/file.c:334
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x6c4/0x1150 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/0x4c0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&of->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x10b0 kernel/locking/mutex.c:760
       kernfs_fop_write_iter+0x28f/0x510 fs/kernfs/file.c:325
       iter_file_splice_write+0x91c/0x1150 fs/splice.c:738
       do_splice_from fs/splice.c:935 [inline]
       do_splice+0x1475/0x1fc0 fs/splice.c:1348
       __do_splice+0x32a/0x360 fs/splice.c:1430
       __do_sys_splice fs/splice.c:1633 [inline]
       __se_sys_splice fs/splice.c:1615 [inline]
       __x64_sys_splice+0x187/0x250 fs/splice.c:1615
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4c0 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 kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x10b0 kernel/locking/mutex.c:760
       pipe_lock fs/pipe.c:91 [inline]
       pipe_lock+0x64/0x80 fs/pipe.c:88
       iter_file_splice_write+0x1ea/0x1150 fs/splice.c:683
       do_splice_from fs/splice.c:935 [inline]
       do_splice+0x1475/0x1fc0 fs/splice.c:1348
       __do_splice+0x32a/0x360 fs/splice.c:1430
       __do_sys_splice fs/splice.c:1633 [inline]
       __se_sys_splice fs/splice.c:1615 [inline]
       __x64_sys_splice+0x187/0x250 fs/splice.c:1615
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4c0 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#6

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(sb_writers#6);
                               lock(&ovl_i_mutex_dir_key[depth]#2);
                               lock(sb_writers#6);
  lock(&pipe->mutex);

 *** DEADLOCK ***

1 lock held by syz.6.2097/14575:
 #0: ffff888076a0a428 (sb_writers#6){.+.+}-{0:0}, at: __do_splice+0x32a/0x360 fs/splice.c:1430

stack backtrace:
CPU: 1 UID: 0 PID: 14575 Comm: syz.6.2097 Not tainted 6.16.0-syzkaller-11105-ga6923c06a3b2 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2043
 check_noncircular+0x14c/0x170 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+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:598 [inline]
 __mutex_lock+0x193/0x10b0 kernel/locking/mutex.c:760
 pipe_lock fs/pipe.c:91 [inline]
 pipe_lock+0x64/0x80 fs/pipe.c:88
 iter_file_splice_write+0x1ea/0x1150 fs/splice.c:683
 do_splice_from fs/splice.c:935 [inline]
 do_splice+0x1475/0x1fc0 fs/splice.c:1348
 __do_splice+0x32a/0x360 fs/splice.c:1430
 __do_sys_splice fs/splice.c:1633 [inline]
 __se_sys_splice fs/splice.c:1615 [inline]
 __x64_sys_splice+0x187/0x250 fs/splice.c:1615
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7787f8eb69
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:00007f7788ddf038 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007f77881b5fa0 RCX: 00007f7787f8eb69
RDX: 000000000000000d RSI: 0000000000000000 RDI: 0000000000000009
RBP: 00007f7788011df1 R08: 0000200000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f77881b5fa0 R15: 00007ffdd1d7eab8
 </TASK>