syzbot

======================================================
WARNING: possible circular locking dependency detected
5.14.0-syzkaller #0 Not tainted
------------------------------------------------------
iou-sqp-7301/7302 is trying to acquire lock:
ffff8880761080a8 (&ctx->uring_lock){+.+.}-{3:3}, at: __io_sq_thread fs/io_uring.c:7291 [inline]
ffff8880761080a8 (&ctx->uring_lock){+.+.}-{3:3}, at: io_sq_thread+0x92c/0x12a0 fs/io_uring.c:7368

but task is already holding lock:
ffff88801b509c70 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread+0x299/0x12a0 fs/io_uring.c:7356

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&sqd->lock){+.+.}-{3:3}:
       lock_acquire+0x19f/0x4d0 kernel/locking/lockdep.c:5625
       __mutex_lock_common+0x1df/0x2550 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:743
       io_register_iowq_max_workers fs/io_uring.c:10551 [inline]
       __io_uring_register fs/io_uring.c:10757 [inline]
       __do_sys_io_uring_register fs/io_uring.c:10792 [inline]
       __se_sys_io_uring_register+0x231e/0x3140 fs/io_uring.c:10772
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (&ctx->uring_lock){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3051 [inline]
       check_prevs_add kernel/locking/lockdep.c:3174 [inline]
       validate_chain+0x1dfb/0x8240 kernel/locking/lockdep.c:3789
       __lock_acquire+0x1382/0x2b00 kernel/locking/lockdep.c:5015
       lock_acquire+0x19f/0x4d0 kernel/locking/lockdep.c:5625
       __mutex_lock_common+0x1df/0x2550 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:743
       __io_sq_thread fs/io_uring.c:7291 [inline]
       io_sq_thread+0x92c/0x12a0 fs/io_uring.c:7368
       ret_from_fork+0x1f/0x30

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sqd->lock);
                               lock(&ctx->uring_lock);
                               lock(&sqd->lock);
  lock(&ctx->uring_lock);

 *** DEADLOCK ***

1 lock held by iou-sqp-7301/7302:
 #0: ffff88801b509c70 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread+0x299/0x12a0 fs/io_uring.c:7356

stack backtrace:
CPU: 1 PID: 7302 Comm: iou-sqp-7301 Not tainted 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1dc/0x2d8 lib/dump_stack.c:106
 check_noncircular+0x2f9/0x3b0 kernel/locking/lockdep.c:2131
 check_prev_add kernel/locking/lockdep.c:3051 [inline]
 check_prevs_add kernel/locking/lockdep.c:3174 [inline]
 validate_chain+0x1dfb/0x8240 kernel/locking/lockdep.c:3789
 __lock_acquire+0x1382/0x2b00 kernel/locking/lockdep.c:5015
 lock_acquire+0x19f/0x4d0 kernel/locking/lockdep.c:5625
 __mutex_lock_common+0x1df/0x2550 kernel/locking/mutex.c:596
 __mutex_lock kernel/locking/mutex.c:729 [inline]
 mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:743
 __io_sq_thread fs/io_uring.c:7291 [inline]
 io_sq_thread+0x92c/0x12a0 fs/io_uring.c:7368
 ret_from_fork+0x1f/0x30