============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.9.5228/21748 is trying to acquire lock:
ffff88802b61d868 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:1039 [inline]
ffff88802b61d868 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: blkdev_buffered_write block/fops.c:734 [inline]
ffff88802b61d868 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: blkdev_write_iter+0xd12/0x11d0 block/fops.c:812

but task is already holding lock:
ffff88802b61d868 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:1039 [inline]
ffff88802b61d868 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: blkdev_write_iter+0xc5e/0x11d0 block/fops.c:811

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&sb->s_type->i_mutex_key#9);
  lock(&sb->s_type->i_mutex_key#9);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

locks held by syz.9.5228/21748: 1, last CPU#3:
 #0: ffff88802b61d868 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:1039 [inline]
 #0: ffff88802b61d868 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: blkdev_write_iter+0xc5e/0x11d0 block/fops.c:811

stack backtrace:
CPU: 3 UID: 0 PID: 21748 Comm: syz.9.5228 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_deadlock_bug.cold+0xbd/0xca kernel/locking/lockdep.c:3085
 check_deadlock kernel/locking/lockdep.c:3137 [inline]
 validate_chain kernel/locking/lockdep.c:3939 [inline]
 __lock_acquire+0x13f4/0x1f40 kernel/locking/lockdep.c:5288
 lock_acquire kernel/locking/lockdep.c:5942 [inline]
 lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5899
 down_read+0x94/0x4c0 kernel/locking/rwsem.c:1574
 inode_lock_shared include/linux/fs.h:1039 [inline]
 blkdev_buffered_write block/fops.c:734 [inline]
 blkdev_write_iter+0xd12/0x11d0 block/fops.c:812
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6af/0x1050 fs/read_write.c:687
 ksys_write+0x12a/0x250 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb9ac59f559
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:00007fb9ad413028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fb9ac826090 RCX: 00007fb9ac59f559
RDX: 0000000000001006 RSI: 0000200000000440 RDI: 0000000000000004
RBP: 00007fb9ac636b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb9ac826128 R14: 00007fb9ac826090 R15: 00007ffc90761f78
 </TASK>