[PATCH 5/6] ext4: Fix fsync error handling after filesystem abort.

[Dmitry Monakhov <dmonakhov@openvz.org>]

If filesystem was aborted after inode's write back is complete
but before its metadata was updated we may return success
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

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
---
 fs/ext4/fsync.c |    8 ++++++--
 fs/ext4/super.c |   12 +++++++++++-
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index e0ba8a4..d7df2f1 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -129,9 +129,13 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 		return ret;
 	mutex_lock(&inode->i_mutex);
 
-	if (inode->i_sb->s_flags & MS_RDONLY)
+	if (inode->i_sb->s_flags & MS_RDONLY) {
+		/* Make shure that we read updated s_mount_flags value */
+		smp_rmb();
+		if (EXT4_SB(inode->i_sb)->s_mount_flags & EXT4_MF_FS_ABORTED)
+			ret = -EROFS;
 		goto out;
-
+	}
 	ret = ext4_flush_unwritten_io(inode);
 	if (ret < 0)
 		goto out;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index edc716d..b4154d3 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -399,6 +399,11 @@ static void ext4_handle_error(struct super_block *sb)
 	}
 	if (test_opt(sb, ERRORS_RO)) {
 		ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");
+		/*
+		 * Make shure updated value of ->s_mount_flags will be visiable
+		 * before ->s_flags update
+		 */
+		smp_wmb();
 		sb->s_flags |= MS_RDONLY;
 	}
 	if (test_opt(sb, ERRORS_PANIC))
@@ -571,8 +576,13 @@ void __ext4_abort(struct super_block *sb, const char *function,
 
 	if ((sb->s_flags & MS_RDONLY) == 0) {
 		ext4_msg(sb, KERN_CRIT, "Remounting filesystem read-only");
-		sb->s_flags |= MS_RDONLY;
 		EXT4_SB(sb)->s_mount_flags |= EXT4_MF_FS_ABORTED;
+		/*
+		 * Make shure updated value of ->s_mount_flags will be visiable
+		 * before ->s_flags update
+		 */
+		smp_wmb();
+		sb->s_flags |= MS_RDONLY;
 		if (EXT4_SB(sb)->s_journal)
 			jbd2_journal_abort(EXT4_SB(sb)->s_journal, -EIO);
 		save_error_info(sb, function, line);
-- 
1.7.1