Re: [syzbot] possible deadlock in f2fs_write_checkpoint

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    6abab1b81b65 Add linux-next specific files for 20220202
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=178ef35bb00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b8d8750556896349
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
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=150341d4700000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15649300700000

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

F2FS-fs (loop0): Can't find valid F2FS filesystem in 2th superblock
F2FS-fs (loop0): invalid crc_offset: 0
F2FS-fs (loop0): Disable nat_bits due to incorrect cp_ver (8221872453892455638, 0)
F2FS-fs (loop0): Try to recover 2th superblock, ret: 0
F2FS-fs (loop0): Mounted with checkpoint version = 7ad43cd6
============================================
WARNING: possible recursive locking detected
5.17.0-rc2-next-20220202-syzkaller #0 Not tainted
--------------------------------------------
syz-executor316/3595 is trying to acquire lock:
ffff88801d514390 (&sem->internal_rwsem#2){++++}-{3:3}, at: f2fs_down_write fs/f2fs/f2fs.h:2156 [inline]
ffff88801d514390 (&sem->internal_rwsem#2){++++}-{3:3}, at: f2fs_write_checkpoint+0x535/0x5c90 fs/f2fs/checkpoint.c:1616

but task is already holding lock:
ffff88801d515398 (&sem->internal_rwsem#2){++++}-{3:3}, at: f2fs_down_write fs/f2fs/f2fs.h:2156 [inline]
ffff88801d515398 (&sem->internal_rwsem#2){++++}-{3:3}, at: f2fs_issue_checkpoint+0x149/0x480 fs/f2fs/checkpoint.c:1835

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

2 locks held by syz-executor316/3595:
 #0: ffff888074db00e0 (&type->s_umount_key#46){+.+.}-{3:3}, at: deactivate_super+0xa5/0xd0 fs/super.c:362
 #1: ffff88801d515398 (&sem->internal_rwsem#2){++++}-{3:3}, at: f2fs_down_write fs/f2fs/f2fs.h:2156 [inline]
 #1: ffff88801d515398 (&sem->internal_rwsem#2){++++}-{3:3}, at: f2fs_issue_checkpoint+0x149/0x480 fs/f2fs/checkpoint.c:1835

stack backtrace:
CPU: 0 PID: 3595 Comm: syz-executor316 Not tainted 5.17.0-rc2-next-20220202-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:2156 [inline]
 f2fs_write_checkpoint+0x535/0x5c90 fs/f2fs/checkpoint.c:1616
 __write_checkpoint_sync fs/f2fs/checkpoint.c:1746 [inline]
 f2fs_issue_checkpoint+0x156/0x480 fs/f2fs/checkpoint.c:1843
 f2fs_sync_fs+0x20f/0x420 fs/f2fs/super.c:1644
 sync_filesystem.part.0+0x13c/0x1d0 fs/sync.c:66
 sync_filesystem+0x8b/0xc0 fs/sync.c:43
 generic_shutdown_super+0x70/0x400 fs/super.c:445
 kill_block_super+0x97/0xf0 fs/super.c:1394
 kill_f2fs_super+0x2b3/0x3c0 fs/f2fs/super.c:4523
 deactivate_locked_super+0x94/0x160 fs/super.c:332
 deactivate_super+0xad/0xd0 fs/super.c:363
 cleanup_mnt+0x3a2/0x540 fs/namespace.c:1159
 task_work_run+0xdd/0x1a0 kernel/task_work.c:164
 exit_task_work include/linux/task_work.h:32 [inline]
 do_exit+0xb29/0x2b10 kernel/exit.c:806
 do_group_exit+0xd2/0x2f0 kernel/exit.c:935
 __do_sys_exit_group kernel/exit.c:946 [inline]
 __se_sys_exit_group kernel/exit.c:944 [inline]
 __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:944
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f93b7998639
Code: Unable to access opcode bytes at RIP 0x7f93b799860f.
RSP: 002b:00007fffe1dc7708 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 00007f93b7a0d3