======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.6.589/10302 is trying to acquire lock:
ffff8881012ad220 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_iop_getattr+0x9e/0x450

but task is already holding lock:
ffff88816d103008 (&q->q_usage_counter(io)#29){++++}-{0:0}, at: lo_ioctl+0x1a51/0x1fb0

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&q->q_usage_counter(io)#29){++++}-{0:0}:
       blk_alloc_queue+0x546/0x680
       __blk_mq_alloc_disk+0x197/0x390
       loop_add+0x482/0xb40
       loop_init+0xd9/0x170
       do_one_initcall+0x250/0x8d0
       do_initcall_level+0x104/0x190
       do_initcalls+0x59/0xa0
       kernel_init_freeable+0x2a6/0x3e0
       kernel_init+0x1d/0x1d0
       ret_from_fork+0x51e/0xb90
       ret_from_fork_asm+0x1a/0x30

-> #1 (fs_reclaim){+.+.}-{0:0}:
       fs_reclaim_acquire+0x71/0x100
       kmem_cache_alloc_noprof+0x40/0x650
       __kernfs_iattrs+0xdf/0x340
       kernfs_iop_setattr+0xea/0x3f0
       notify_change+0xc1a/0xf40
       do_truncate+0x1c2/0x250
       path_openat+0x2f89/0x3860
       do_file_open+0x23e/0x4a0
       do_sys_openat2+0x113/0x200
       __x64_sys_openat+0x138/0x170
       do_syscall_64+0x14d/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}:
       __lock_acquire+0x15a5/0x2cf0
       lock_acquire+0xf0/0x2e0
       down_read+0x47/0x2e0
       kernfs_iop_getattr+0x9e/0x450
       vfs_getattr_nosec+0x2e1/0x430
       loop_assign_backing_file+0x27a/0x4b0
       lo_ioctl+0x1acb/0x1fb0
       blkdev_ioctl+0x5e3/0x740
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x14d/0xf80
       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)#29

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->q_usage_counter(io)#29);
                               lock(fs_reclaim);
                               lock(&q->q_usage_counter(io)#29);
  rlock(&root->kernfs_iattr_rwsem);

 *** DEADLOCK ***

3 locks held by syz.6.589/10302:
 #0: ffff88816d10e448 (&lo->lo_mutex){+.+.}-{4:4}, at: lo_ioctl+0x14c7/0x1fb0
 #1: ffff88816d103008 (&q->q_usage_counter(io)#29){++++}-{0:0}, at: lo_ioctl+0x1a51/0x1fb0
 #2: ffff88816d103040 (&q->q_usage_counter(queue)#13){+.+.}-{0:0}, at: lo_ioctl+0x1a51/0x1fb0

stack backtrace:
CPU: 0 UID: 0 PID: 10302 Comm: syz.6.589 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+0xe8/0x150
 print_circular_bug+0x2e1/0x300
 check_noncircular+0x12e/0x150
 __lock_acquire+0x15a5/0x2cf0
 lock_acquire+0xf0/0x2e0
 down_read+0x47/0x2e0
 kernfs_iop_getattr+0x9e/0x450
 vfs_getattr_nosec+0x2e1/0x430
 loop_assign_backing_file+0x27a/0x4b0
 lo_ioctl+0x1acb/0x1fb0
 blkdev_ioctl+0x5e3/0x740
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0x14d/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb08099c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb07ebf6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fb080c16090 RCX: 00007fb08099c819
RDX: 0000000000000003 RSI: 0000000000004c06 RDI: 000000000000000b
RBP: 00007fb080a32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb080c16128 R14: 00007fb080c16090 R15: 00007ffc8ca3cd18
 </TASK>
