======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.2.2398/12246 is trying to acquire lock:
ffff8881012d4a10 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_iop_getattr+0x9e/0x450

but task is already holding lock:
ffff88816b967020 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: lo_ioctl+0x1a65/0x1fc0

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}:
       blk_alloc_queue+0x544/0x690
       __blk_mq_alloc_disk+0x194/0x390
       loop_add+0x480/0xb40
       loop_init+0xd7/0x160
       do_one_initcall+0x250/0x870
       do_initcall_level+0x10a/0x1a0
       do_initcalls+0x59/0xa0
       kernel_init_freeable+0x29d/0x3e0
       kernel_init+0x1d/0x1d0
       ret_from_fork+0x514/0xb70
       ret_from_fork_asm+0x1a/0x30

-> #1 (fs_reclaim){+.+.}-{0:0}:
       fs_reclaim_acquire+0x71/0x100
       kmem_cache_alloc_noprof+0x64/0x5f0
       __kernfs_iattrs+0xdd/0x380
       kernfs_iop_setattr+0xe6/0x3f0
       notify_change+0xbba/0xea0
       do_truncate+0x1c2/0x250
       path_openat+0x2fed/0x3830
       do_file_open+0x23e/0x4a0
       do_sys_openat2+0x115/0x200
       __x64_sys_openat+0x138/0x170
       do_syscall_64+0x174/0x580
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}:
       __lock_acquire+0x1520/0x2cf0
       lock_acquire+0x106/0x350
       down_read+0x4a/0x330
       kernfs_iop_getattr+0x9e/0x450
       vfs_getattr_nosec+0x2e1/0x430
       loop_assign_backing_file+0x27a/0x4b0
       lo_ioctl+0x1ad6/0x1fc0
       blkdev_ioctl+0x5e3/0x740
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x174/0x580
       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.2.2398/12246:
 #0: ffff88816bc8c430 (&lo->lo_mutex){+.+.}-{4:4}, at: lo_ioctl+0x14c7/0x1fc0
 #1: ffff88816b967020 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: lo_ioctl+0x1a65/0x1fc0
 #2: ffff88816b967058 (&q->q_usage_counter(queue)#8){+.+.}-{0:0}, at: lo_ioctl+0x1a65/0x1fc0

stack backtrace:
CPU: 1 UID: 0 PID: 12246 Comm: syz.2.2398 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
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+0x1520/0x2cf0
 lock_acquire+0x106/0x350
 down_read+0x4a/0x330
 kernfs_iop_getattr+0x9e/0x450
 vfs_getattr_nosec+0x2e1/0x430
 loop_assign_backing_file+0x27a/0x4b0
 lo_ioctl+0x1ad6/0x1fc0
 blkdev_ioctl+0x5e3/0x740
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0x174/0x580
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb82f99e0d9
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:00007fb830905028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fb82fc25fa0 RCX: 00007fb82f99e0d9
RDX: 0000000000000004 RSI: 0000000000004c06 RDI: 0000000000000003
RBP: 00007fb82fa35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb82fc26038 R14: 00007fb82fc25fa0 R15: 00007fff1f3a5488
 </TASK>
ldm_validate_partition_table(): Disk read failed.
Dev loop7: unable to read RDB block 0
 loop7: unable to read partition table
loop7: partition table beyond EOD, truncated
loop_reread_partitions: partition scan of loop7 () failed (rc=-5)
