vfs: ignore error on forced remount

On emergency remount we want to force MS_RDONLY on the super block
even if ->remount_fs() failed for some reason.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Tested-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

fs/super.c

@@ -727,8 +727,13 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
 
 	if (sb->s_op->remount_fs) {
 		retval = sb->s_op->remount_fs(sb, &flags, data);
-		if (retval)
-			return retval;
+		if (retval) {
+			if (!force)
+				return retval;
+			/* If forced remount, go ahead despite any errors */
+			WARN(1, "forced remount of a %s fs returned %i\n",
+			     sb->s_type->name, retval);
+		}
 	}
 	sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);