======================================================
WARNING: possible circular locking dependency detected
5.13.0-rc5-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor708/8403 is trying to acquire lock:
ffff88814572c5a0 (&bdev->bd_mutex){+.+.}-{3:3}, at: del_gendisk+0x2ab/0x860 block/genhd.c:610

but task is already holding lock:
ffffffff8d671668 (loop_ctl_mutex){+.+.}-{3:3}, at: loop_control_ioctl+0x9b/0x770 drivers/block/loop.c:2257

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (loop_ctl_mutex){+.+.}-{3:3}:
       lock_acquire+0x17f/0x720 kernel/locking/lockdep.c:5512
       __mutex_lock_common+0x1bf/0x3100 kernel/locking/mutex.c:959
       __mutex_lock kernel/locking/mutex.c:1104 [inline]
       mutex_lock_killable_nested+0x1a/0x20 kernel/locking/mutex.c:1134
       lo_open+0x1c/0x100 drivers/block/loop.c:1890
       __blkdev_get+0x293/0xa50 fs/block_dev.c:1311
       blkdev_get_by_dev+0xf9/0x640 fs/block_dev.c:1451
       blkdev_open+0x132/0x2c0 fs/block_dev.c:1546
       do_dentry_open+0x7cb/0x1010 fs/open.c:826
       do_open fs/namei.c:3361 [inline]
       path_openat+0x28e6/0x39b0 fs/namei.c:3494
       do_filp_open+0x221/0x460 fs/namei.c:3521
       do_sys_openat2+0x124/0x460 fs/open.c:1187
       do_sys_open fs/open.c:1203 [inline]
       __do_sys_open fs/open.c:1211 [inline]
       __se_sys_open fs/open.c:1207 [inline]
       __x64_sys_open+0x221/0x270 fs/open.c:1207
       do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (&bdev->bd_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:2938 [inline]
       check_prevs_add+0x4f9/0x5b60 kernel/locking/lockdep.c:3061
       validate_chain kernel/locking/lockdep.c:3676 [inline]
       __lock_acquire+0x4307/0x6040 kernel/locking/lockdep.c:4902
       lock_acquire+0x17f/0x720 kernel/locking/lockdep.c:5512
       __mutex_lock_common+0x1bf/0x3100 kernel/locking/mutex.c:959
       __mutex_lock kernel/locking/mutex.c:1104 [inline]
       mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1119
       del_gendisk+0x2ab/0x860 block/genhd.c:610
       loop_remove drivers/block/loop.c:2191 [inline]
       loop_control_ioctl+0x647/0x770 drivers/block/loop.c:2291
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:1069 [inline]
       __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:1055
       do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
       entry_SYSCALL_64_after_hwframe+0x44/0xae

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(loop_ctl_mutex);
                               lock(&bdev->bd_mutex);
                               lock(loop_ctl_mutex);
  lock(&bdev->bd_mutex);

 *** DEADLOCK ***

1 lock held by syz-executor708/8403:
 #0: ffffffff8d671668 (loop_ctl_mutex){+.+.}-{3:3}, at: loop_control_ioctl+0x9b/0x770 drivers/block/loop.c:2257

stack backtrace:
CPU: 1 PID: 8403 Comm: syz-executor708 Not tainted 5.13.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x202/0x31e lib/dump_stack.c:120
 print_circular_bug+0xb17/0xdc0 kernel/locking/lockdep.c:2007
 check_noncircular+0x2cc/0x390 kernel/locking/lockdep.c:2129
 check_prev_add kernel/locking/lockdep.c:2938 [inline]
 check_prevs_add+0x4f9/0x5b60 kernel/locking/lockdep.c:3061
 validate_chain kernel/locking/lockdep.c:3676 [inline]
 __lock_acquire+0x4307/0x6040 kernel/locking/lockdep.c:4902
 lock_acquire+0x17f/0x720 kernel/locking/lockdep.c:5512
 __mutex_lock_common+0x1bf/0x3100 kernel/locking/mutex.c:959
 __mutex_lock kernel/locking/mutex.c:1104 [inline]
 mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1119
 del_gendisk+0x2ab/0x860 block/genhd.c:610
 loop_remove drivers/block/loop.c:2191 [inline]
 loop_control_ioctl+0x647/0x770 drivers/block/loop.c:2291
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:1055
 do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x43ee49
Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd041439f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000400488 RCX: 000000000043ee49
RDX: 0000000000000000 RSI: 0000000000004c81 RDI: 0000000000000003
RBP: 0000000000402e30 R08: 0000000000000000 R09: 0000000000400488
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402ec0
R13: 0000000000000000 R14: 00000000004ac018 R15: 0000000000400488