[syzbot] possible deadlock in f2fs_write_checkpoint

[syzbot <syzbot+0b9cadf5fc45a98a5083@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    57c149e506d5 Add linux-next specific files for 20220110
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15cb8b77b00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2f1cca5543ac6349
dashboard link: https://syzkaller.appspot.com/bug?extid=0b9cadf5fc45a98a5083
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0b9cadf5fc45a98a5083@syzkaller.appspotmail.com

============================================
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>


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