linux-kernel - Re: [PATCH 2/2 v2] f2fs: complete checkpoints during remount

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Message-ID: <YwaKbmB23U9czf51@google.com>
Date:   Wed, 24 Aug 2022 13:30:38 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH 2/2 v2] f2fs: complete checkpoints during remount

Otherwise, pending checkpoints can contribute a race condition to give a
quota warning.

- Thread                      - checkpoint thread
                              add checkpoints to the list
do_remount()
 down_write(&sb->s_umount);
 f2fs_remount()
                              block_operations()
                               down_read_trylock(&sb->s_umount) = 0
 up_write(&sb->s_umount);
                               f2fs_quota_sync()
                                dquot_writeback_dquots()
                                 WARN_ON_ONCE(!rwsem_is_locked(&sb->s_umount));

Or,

do_remount()
 down_write(&sb->s_umount);
 f2fs_remount()
                              create a ckpt thread
                              f2fs_enable_checkpoint() adds checkpoints
			      wait for f2fs_sync_fs()
                              trigger another pending checkpoint
                               block_operations()
                                down_read_trylock(&sb->s_umount) = 0
 up_write(&sb->s_umount);
                                f2fs_quota_sync()
                                 dquot_writeback_dquots()
                                  WARN_ON_ONCE(!rwsem_is_locked(&sb->s_umount));

Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
---

 Change log from v1:
  - add one more case

 fs/f2fs/super.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 4f2ff50b247c..0f29c759a898 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2185,6 +2185,9 @@ static void f2fs_enable_checkpoint(struct f2fs_sb_info *sbi)
 	f2fs_up_write(&sbi->gc_lock);
 
 	f2fs_sync_fs(sbi->sb, 1);
+
+	/* Let's ensure there's no pending checkpoint anymore */
+	f2fs_flush_ckpt_thread(sbi);
 }
 
 static int f2fs_remount(struct super_block *sb, int *flags, char *data)
@@ -2350,6 +2353,9 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
 		f2fs_stop_ckpt_thread(sbi);
 		need_restart_ckpt = true;
 	} else {
+		/* Flush if the prevous checkpoint, if exists. */
+		f2fs_flush_ckpt_thread(sbi);
+
 		err = f2fs_start_ckpt_thread(sbi);
 		if (err) {
 			f2fs_err(sbi,
-- 
2.37.1.595.g718a3a8f04-goog