======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.1.19423/7980 is trying to acquire lock:
ffff8881078a8600 (&sb->s_type->i_mutex_key#24){++++}-{4:4}, at: configfs_depend_item_unlocked+0x153/0x420

but task is already holding lock:
ffffffff8fc6dc60 (tpg_instances_lock){+.+.}-{4:4}, at: usbg_make_tpg+0xf8/0x550

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (tpg_instances_lock){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       usbg_make_tpg+0xf8/0x550
       target_fabric_make_tpg+0xa8/0x6d0
       configfs_mkdir+0x4f6/0x9e0
       vfs_mkdir+0x40c/0x620
       filename_mkdirat+0x285/0x510
       __se_sys_mkdir+0x34/0x150
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&subsys->su_mutex){+.+.}-{4:4}:
       __mutex_lock+0x19d/0x1550
       configfs_rmdir+0x5f0/0x950
       vfs_rmdir+0x3e6/0x6a0
       filename_rmdir+0x292/0x520
       __se_sys_rmdir+0x2e/0x140
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&sb->s_type->i_mutex_key#24){++++}-{4:4}:
       __lock_acquire+0x15ff/0x2e50
       lock_acquire+0x115/0x350
       down_write+0x96/0x200
       configfs_depend_item_unlocked+0x153/0x420
       usbg_make_tpg+0x1e0/0x550
       target_fabric_make_tpg+0xa8/0x6d0
       configfs_mkdir+0x4f6/0x9e0
       vfs_mkdir+0x40c/0x620
       filename_mkdirat+0x285/0x510
       __se_sys_mkdir+0x34/0x150
       do_syscall_64+0x166/0x520
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &sb->s_type->i_mutex_key#24 --> &subsys->su_mutex --> tpg_instances_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(tpg_instances_lock);
                               lock(&subsys->su_mutex);
                               lock(tpg_instances_lock);
  lock(&sb->s_type->i_mutex_key#24);

 *** DEADLOCK ***

locks held by syz.1.19423/7980: 4, last CPU#0:
 #0: ffff888108f18460 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90
 #1: ffff88811eb5d440 (&sb->s_type->i_mutex_key#8/1){+.+.}-{4:4}, at: filename_create+0x200/0x370
 #2: ffffffff8f938528 (&subsys->su_mutex){+.+.}-{4:4}, at: configfs_mkdir+0x4b0/0x9e0
 #3: ffffffff8fc6dc60 (tpg_instances_lock){+.+.}-{4:4}, at: usbg_make_tpg+0xf8/0x550

stack backtrace:
CPU: 0 UID: 0 PID: 7980 Comm: syz.1.19423 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+0x2e2/0x300
 check_noncircular+0x12f/0x150
 __lock_acquire+0x15ff/0x2e50
 lock_acquire+0x115/0x350
 down_write+0x96/0x200
 configfs_depend_item_unlocked+0x153/0x420
 usbg_make_tpg+0x1e0/0x550
 target_fabric_make_tpg+0xa8/0x6d0
 configfs_mkdir+0x4f6/0x9e0
 vfs_mkdir+0x40c/0x620
 filename_mkdirat+0x285/0x510
 __se_sys_mkdir+0x34/0x150
 do_syscall_64+0x166/0x520
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1a1c39e159
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:00007f1a1a5d5028 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
RAX: ffffffffffffffda RBX: 00007f1a1c626090 RCX: 00007f1a1c39e159
RDX: 0000000000000000 RSI: 00000000000001ff RDI: 0000200000000600
RBP: 00007f1a1c435024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1a1c626128 R14: 00007f1a1c626090 R15: 00007ffeace0d898
 </TASK>
