linux-kernel - [PATCH 5.15 081/530] f2fs: complete checkpoints during remount

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Message-Id: <20221024113048.676219749@linuxfoundation.org>
Date:   Mon, 24 Oct 2022 13:27:05 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Chao Yu <chao@...nel.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>
Subject: [PATCH 5.15 081/530] f2fs: complete checkpoints during remount

From: Jaegeuk Kim <jaegeuk@...nel.org>

commit 4f99484d27961cb194cebcd917176fa038a5025f upstream.

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));

Cc: stable@...r.kernel.org
Reviewed-by: Chao Yu <chao@...nel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/f2fs/super.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2152,6 +2152,9 @@ static void f2fs_enable_checkpoint(struc
 	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)
@@ -2318,6 +2321,9 @@ static int f2fs_remount(struct super_blo
 		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,