ext4: fix warning when submitting superblock in ext4_commit_super()

We have already check the io_error and uptodate flag before submitting
the superblock buffer, and re-set the uptodate flag if it has been
failed to write out. But it was lockless and could be raced by another
ext4_commit_super(), and finally trigger '!uptodate' WARNING when
marking buffer dirty. Fix it by submit buffer directly.

Reported-by: Hulk Robot <[email protected]>
Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Reviewed-by: Ritesh Harjani <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

Author: zhangyi089

fs/ext4/super.c

@@ -5898,7 +5898,6 @@ static void ext4_update_super(struct super_block *sb)
 static int ext4_commit_super(struct super_block *sb)
 {
 	struct buffer_head *sbh = EXT4_SB(sb)->s_sbh;
-	int error = 0;
 
 	if (!sbh)
 		return -EINVAL;
@@ -5907,6 +5906,13 @@ static int ext4_commit_super(struct super_block *sb)
 
 	ext4_update_super(sb);
 
+	lock_buffer(sbh);
+	/* Buffer got discarded which means block device got invalidated */
+	if (!buffer_mapped(sbh)) {
+		unlock_buffer(sbh);
+		return -EIO;
+	}
+
 	if (buffer_write_io_error(sbh) || !buffer_uptodate(sbh)) {
 		/*
 		 * Oh, dear.  A previous attempt to write the
@@ -5921,17 +5927,21 @@ static int ext4_commit_super(struct super_block *sb)
 		clear_buffer_write_io_error(sbh);
 		set_buffer_uptodate(sbh);
 	}
-	BUFFER_TRACE(sbh, "marking dirty");
-	mark_buffer_dirty(sbh);
-	error = __sync_dirty_buffer(sbh,
-		REQ_SYNC | (test_opt(sb, BARRIER) ? REQ_FUA : 0));
+	get_bh(sbh);
+	/* Clear potential dirty bit if it was journalled update */
+	clear_buffer_dirty(sbh);
+	sbh->b_end_io = end_buffer_write_sync;
+	submit_bh(REQ_OP_WRITE,
+		  REQ_SYNC | (test_opt(sb, BARRIER) ? REQ_FUA : 0), sbh);
+	wait_on_buffer(sbh);
 	if (buffer_write_io_error(sbh)) {
 		ext4_msg(sb, KERN_ERR, "I/O error while writing "
 		       "superblock");
 		clear_buffer_write_io_error(sbh);
 		set_buffer_uptodate(sbh);
+		return -EIO;
 	}
-	return error;
+	return 0;
 }
 
 /*