============================================
WARNING: possible recursive locking detected
5.16.0-rc8-next-20220110-syzkaller #0 Not tainted
--------------------------------------------
f2fs_ckpt-7:2/4139 is trying to acquire lock:
ffff88807c598390 (&sem->internal_rwsem#2){+.+.}-{3:3}, at: f2fs_down_write fs/f2fs/f2fs.h:2149 [inline]
ffff88807c598390 (&sem->internal_rwsem#2){+.+.}-{3:3}, at: f2fs_write_checkpoint+0x535/0x5d00 fs/f2fs/checkpoint.c:1615

but task is already holding lock:
ffff88807c599338 (&sem->internal_rwsem#2){+.+.}-{3:3}, at: f2fs_down_write fs/f2fs/f2fs.h:2149 [inline]
ffff88807c599338 (&sem->internal_rwsem#2){+.+.}-{3:3}, at: __write_checkpoint_sync fs/f2fs/checkpoint.c:1744 [inline]
ffff88807c599338 (&sem->internal_rwsem#2){+.+.}-{3:3}, at: __checkpoint_and_complete_reqs+0xdd/0x360 fs/f2fs/checkpoint.c:1764

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

       CPU0
       ----
  lock(&sem->internal_rwsem#2);
  lock(&sem->internal_rwsem#2);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

1 lock held by f2fs_ckpt-7:2/4139:
 #0: ffff88807c599338 (&sem->internal_rwsem#2){+.+.}-{3:3}, at: f2fs_down_write fs/f2fs/f2fs.h:2149 [inline]
 #0: ffff88807c599338 (&sem->internal_rwsem#2){+.+.}-{3:3}, at: __write_checkpoint_sync fs/f2fs/checkpoint.c:1744 [inline]
 #0: ffff88807c599338 (&sem->internal_rwsem#2){+.+.}-{3:3}, at: __checkpoint_and_complete_reqs+0xdd/0x360 fs/f2fs/checkpoint.c:1764

stack backtrace:
CPU: 0 PID: 4139 Comm: f2fs_ckpt-7:2 Not tainted 5.16.0-rc8-next-20220110-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_deadlock_bug kernel/locking/lockdep.c:2956 [inline]
 check_deadlock kernel/locking/lockdep.c:2999 [inline]
 validate_chain kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire.cold+0x149/0x3ab kernel/locking/lockdep.c:5027
 lock_acquire kernel/locking/lockdep.c:5639 [inline]
 lock_acquire+0x1ab/0x510 kernel/locking/lockdep.c:5604
 down_write+0x90/0x150 kernel/locking/rwsem.c:1514
 f2fs_down_write fs/f2fs/f2fs.h:2149 [inline]
 f2fs_write_checkpoint+0x535/0x5d00 fs/f2fs/checkpoint.c:1615
 __write_checkpoint_sync fs/f2fs/checkpoint.c:1745 [inline]
 __checkpoint_and_complete_reqs+0xea/0x360 fs/f2fs/checkpoint.c:1764
 issue_checkpoint_thread+0xdf/0x250 fs/f2fs/checkpoint.c:1795
 kthread+0x2e9/0x3a0 kernel/kthread.c:377
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>