ext3: Fix fsync error handling after filesystem abort.

If filesystem was aborted we will return success
due to (sb->s_flags & MS_RDONLY) which is incorrect and
results in data loss.
In order to handle fs abort correctly we have to check
fs state once we discover that it is in MS_RDONLY state

Test case: http://patchwork.ozlabs.org/patch/244297/
Changes from V1:
 - fix spelling
 - fix smp_rmb()/debug order
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ext3/fsync.c

@@ -48,9 +48,13 @@ int ext3_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 
 	trace_ext3_sync_file_enter(file, datasync);
 
-	if (inode->i_sb->s_flags & MS_RDONLY)
+	if (inode->i_sb->s_flags & MS_RDONLY) {
+		/* Make sure that we read updated state */
+		smp_rmb();
+		if (EXT3_SB(inode->i_sb)->s_mount_state & EXT3_ERROR_FS)
+			return -EROFS;
 		return 0;
-
+	}
 	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
 	if (ret)
 		goto out;

fs/ext3/super.c

@@ -174,6 +174,11 @@ static void ext3_handle_error(struct super_block *sb)
 	if (test_opt (sb, ERRORS_RO)) {
 		ext3_msg(sb, KERN_CRIT,
 			"error: remounting filesystem read-only");
+		/*
+		 * Make sure updated value of ->s_mount_state will be visible
+		 * before ->s_flags update.
+		 */
+		smp_wmb();
 		sb->s_flags |= MS_RDONLY;
 	}
 	ext3_commit_super(sb, es, 1);
@@ -291,8 +296,14 @@ void ext3_abort(struct super_block *sb, const char *function,
 	ext3_msg(sb, KERN_CRIT,
 		"error: remounting filesystem read-only");
 	EXT3_SB(sb)->s_mount_state |= EXT3_ERROR_FS;
-	sb->s_flags |= MS_RDONLY;
 	set_opt(EXT3_SB(sb)->s_mount_opt, ABORT);
+	/*
+	 * Make sure updated value of ->s_mount_state will be visible
+	 * before ->s_flags update.
+	 */
+	smp_wmb();
+	sb->s_flags |= MS_RDONLY;
+
 	if (EXT3_SB(sb)->s_journal)
 		journal_abort(EXT3_SB(sb)->s_journal, -EIO);
 }