Patch "ocfs2: fix start offset to ocfs2_zero_range_for_truncate()" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

ocfs2: fix start offset to ocfs2_zero_range_for_truncate()

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ocfs2-fix-start-offset-to-ocfs2_zero_range_for_truncate.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ashish Samant <[email protected]>
Date: Mon, 19 Sep 2016 14:44:42 -0700
Subject: ocfs2: fix start offset to ocfs2_zero_range_for_truncate()

From: Ashish Samant <[email protected]>

commit d21c353d5e99c56cdd5b5c1183ffbcaf23b8b960 upstream.

If we punch a hole on a reflink such that following conditions are met:

1. start offset is on a cluster boundary
2. end offset is not on a cluster boundary
3. (end offset is somewhere in another extent) or
(hole range > MAX_CONTIG_BYTES(1MB)),

we dont COW the first cluster starting at the start offset. But in this case, we were wrongly passing this cluster to ocfs2_zero_range_for_truncate() to zero out. This will modify the cluster in place and zero it in the source too.

Fix this by skipping this cluster in such a scenario.

To reproduce:

1. Create a random file of say 10 MB

     xfs_io -c 'pwrite -b 4k 0 10M' -f 10MBfile

2. Reflink it
reflink -f 10MBfile reflnktest
3. Punch a hole at starting at cluster boundary with range greater that 1MB. You can also use a range that will put the end offset in another extent.

     fallocate -p -o 0 -l 1048615 reflnktest

4. sync
5. Check the first cluster in the source file. (It will be zeroed out). dd if=10MBfile iflag=direct bs=<cluster size> count=1 | hexdump -C

---
 fs/ocfs2/file.c |   38 ++++++++++++++++++++++++++------------
 1 file changed, 26 insertions(+), 12 deletions(-)

@@ -1536,7 +1536,8 @@ static int ocfs2_zero_partial_clusters(s
 				       u64 start, u64 len)
 {
 	int ret = 0;
-	u64 tmpend, end = start + len;
+	u64 tmpend = 0;
+	u64 end = start + len;
 	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
 	unsigned int csize = osb->s_clustersize;
 	handle_t *handle;

@@ -1568,18 +1569,31 @@ static int ocfs2_zero_partial_clusters(s
 	}
 
 	/*
-	 * We want to get the byte offset of the end of the 1st cluster.
+	 * If start is on a cluster boundary and end is somewhere in another
+	 * cluster, we have not COWed the cluster starting at start, unless
+	 * end is also within the same cluster. So, in this case, we skip this
+	 * first call to ocfs2_zero_range_for_truncate() truncate and move on
+	 * to the next one.
 	 */
-	tmpend = (u64)osb->s_clustersize + (start & ~(osb->s_clustersize - 1));
-	if (tmpend > end)
-		tmpend = end;
-
-	trace_ocfs2_zero_partial_clusters_range1((unsigned long long)start,
-						 (unsigned long long)tmpend);
-
-	ret = ocfs2_zero_range_for_truncate(inode, handle, start, tmpend);
-	if (ret)
-		mlog_errno(ret);
+	if ((start & (csize - 1)) != 0) {
+		/*
+		 * We want to get the byte offset of the end of the 1st
+		 * cluster.
+		 */
+		tmpend = (u64)osb->s_clustersize +
+			(start & ~(osb->s_clustersize - 1));
+		if (tmpend > end)
+			tmpend = end;
+
+		trace_ocfs2_zero_partial_clusters_range1(
+			(unsigned long long)start,
+			(unsigned long long)tmpend);
+
+		ret = ocfs2_zero_range_for_truncate(inode, handle, start,
+						    tmpend);
+		if (ret)
+			mlog_errno(ret);
+	}
 
 	if (tmpend < end) {
 		/*

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/ocfs2-fix-start-offset-to-ocfs2_zero_range_for_truncate.patch