ocfs2: Fix start offset to ocfs2_zero_range_for_truncate()

If we do fallocate with punch hole option on a reflink, with start offset on a cluster boundary and end offset somewhere in another cluster, 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.

Fix this by skipping this cluster in such a scenario.

Signed-off-by Ashish Samant <[email protected]>

---
  fs/ocfs2/file.c | 34 ++++++++++++++++++++++++----------
  1 file changed, 24 insertions(+), 10 deletions(-)

fs/ocfs2/file.c +24 -10

index 4a6e130..ab305aa 100644
@@ -1522,7 +1522,8 @@ static int ocfs2_zero_partial_clusters(struct inode *inode,
  				       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;

@@ -1554,18 +1555,31 @@ static int ocfs2_zero_partial_clusters(struct inode *inode,
  	}
 
  	/*
-	 * 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;
+	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);
+		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);
+		ret = ocfs2_zero_range_for_truncate(inode, handle, start,
+						    tmpend);
+		if (ret)
+			mlog_errno(ret);
+	}
 
  	if (tmpend < end) {
  		/*

If we do fallocate with punch hole option on a reflink, with start offset on a cluster boundary and end offset somewhere in another cluster, 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.

Fix this by skipping this cluster in such a scenario.

Quoted 6 lines · On Thu, 11 Aug 2016 16:12:27 -0700 Ashish Samant <[email protected]>…

If we do fallocate with punch hole option on a reflink, with start offset on a cluster boundary and end offset somewhere in another cluster, 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.

Quoted 1 line

Fix this by skipping this cluster in such a scenario.

How serious is this bug? It sounds like a data-corrupting error? As such, this is a high priority fix and it should be backported into the -stable kernels?

Please always include such info when fixing bugs.