ext2: avoid WARN() messages when failing to write to the superblock

This fixes a common warning reported by kerneloops.org

[Kernel summit hacking hour]
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ext2/super.c

@@ -1105,9 +1105,30 @@ failed_sbi:
 	return ret;
 }
 
+static void ext2_clear_super_error(struct super_block *sb)
+{
+	struct buffer_head *sbh = EXT2_SB(sb)->s_sbh;
+
+	if (buffer_write_io_error(sbh)) {
+		/*
+		 * Oh, dear.  A previous attempt to write the
+		 * superblock failed.  This could happen because the
+		 * USB device was yanked out.  Or it could happen to
+		 * be a transient write error and maybe the block will
+		 * be remapped.  Nothing we can do but to retry the
+		 * write and hope for the best.
+		 */
+		printk(KERN_ERR "EXT2-fs: %s previous I/O error to "
+		       "superblock detected", sb->s_id);
+		clear_buffer_write_io_error(sbh);
+		set_buffer_uptodate(sbh);
+	}
+}
+
 static void ext2_commit_super (struct super_block * sb,
 			       struct ext2_super_block * es)
 {
+	ext2_clear_super_error(sb);
 	es->s_wtime = cpu_to_le32(get_seconds());
 	mark_buffer_dirty(EXT2_SB(sb)->s_sbh);
 	sb->s_dirt = 0;
@@ -1115,6 +1136,7 @@ static void ext2_commit_super (struct super_block * sb,
 
 static void ext2_sync_super(struct super_block *sb, struct ext2_super_block *es)
 {
+	ext2_clear_super_error(sb);
 	es->s_free_blocks_count = cpu_to_le32(ext2_count_free_blocks(sb));
 	es->s_free_inodes_count = cpu_to_le32(ext2_count_free_inodes(sb));
 	es->s_wtime = cpu_to_le32(get_seconds());