======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.4.520/8580 is trying to acquire lock:
ffff8881000e0220 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_iop_getattr+0x9e/0x450

but task is already holding lock:
ffff888108efe2c8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: lo_ioctl+0x16cc/0x1c10

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&q->q_usage_counter(io)#24){++++}-{0:0}:
       lock_acquire+0x120/0x360
       blk_alloc_queue+0x538/0x620
       __blk_mq_alloc_disk+0x15c/0x340
       loop_add+0x411/0xad0
       loop_init+0xd9/0x170
       do_one_initcall+0x236/0x820
       do_initcall_level+0x104/0x190
       do_initcalls+0x59/0xa0
       kernel_init_freeable+0x334/0x4b0
       kernel_init+0x1d/0x1d0
       ret_from_fork+0x439/0x7d0
       ret_from_fork_asm+0x1a/0x30

-> #1 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire+0x120/0x360
       fs_reclaim_acquire+0x72/0x100
       kmem_cache_alloc_noprof+0x44/0x3c0
       __kernfs_iattrs+0xd9/0x320
       kernfs_iop_setattr+0xea/0x3f0
       notify_change+0xb36/0xe40
       do_truncate+0x1a4/0x220
       path_openat+0x306c/0x3830
       do_filp_open+0x1fa/0x410
       do_sys_openat2+0x121/0x1c0
       __x64_sys_openat+0x138/0x170
       do_syscall_64+0xfa/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}:
       validate_chain+0xb9b/0x2140
       __lock_acquire+0xab9/0xd20
       lock_acquire+0x120/0x360
       down_read+0x46/0x2e0
       kernfs_iop_getattr+0x9e/0x450
       vfs_getattr_nosec+0x2e1/0x430
       loop_assign_backing_file+0x222/0x400
       lo_ioctl+0x1738/0x1c10
       blkdev_ioctl+0x5a8/0x6d0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &root->kernfs_iattr_rwsem --> fs_reclaim --> &q->q_usage_counter(io)#24

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->q_usage_counter(io)#24);
                               lock(fs_reclaim);
                               lock(&q->q_usage_counter(io)#24);
  rlock(&root->kernfs_iattr_rwsem);

 *** DEADLOCK ***

3 locks held by syz.4.520/8580:
 #0: ffff8880201bc400 (&lo->lo_mutex){+.+.}-{4:4}, at: lo_ioctl+0x11c1/0x1c10
 #1: ffff888108efe2c8 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: lo_ioctl+0x16cc/0x1c10
 #2: ffff888108efe300 (&q->q_usage_counter(queue)#8){+.+.}-{0:0}, at: lo_ioctl+0x16cc/0x1c10

stack backtrace:
CPU: 0 UID: 0 PID: 8580 Comm: syz.4.520 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250
 print_circular_bug+0x2ee/0x310
 check_noncircular+0x134/0x160
 validate_chain+0xb9b/0x2140
 __lock_acquire+0xab9/0xd20
 lock_acquire+0x120/0x360
 down_read+0x46/0x2e0
 kernfs_iop_getattr+0x9e/0x450
 vfs_getattr_nosec+0x2e1/0x430
 loop_assign_backing_file+0x222/0x400
 lo_ioctl+0x1738/0x1c10
 blkdev_ioctl+0x5a8/0x6d0
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f942e38ec29
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:00007f942f1e8038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f942e5d5fa0 RCX: 00007f942e38ec29
RDX: 0000000000000018 RSI: 0000000000004c06 RDI: 0000000000000003
RBP: 00007f942e411e41 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f942e5d6038 R14: 00007f942e5d5fa0 R15: 00007ffcc0475e38
 </TASK>
