ocfs2: Count more refcount records in file system fragmentation.

The refcount record calculation in ocfs2_calc_refcount_meta_credits
is too optimistic that we can always allocate contiguous clusters
and handle an already existed refcount rec as a whole. Actually
because of file system fragmentation, we may have the chance to split
a refcount record into 3 parts during the transaction. So consider
the worst case in record calculation.

Cc: stable@kernel.org
Signed-off-by: Tao Ma <tao.ma@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

1 files changed, 15 insertions, 5 deletions

diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
index 3ac5aa733e9c..73a11ccfd4c2 100644
--- a/fs/ocfs2/refcounttree.c
+++ b/fs/ocfs2/refcounttree.c
@@ -2436,16 +2436,26 @@ static int ocfs2_calc_refcount_meta_credits(struct super_block *sb,
                 len = min((u64)cpos + clusters, le64_to_cpu(rec.r_cpos) +
                           le32_to_cpu(rec.r_clusters)) - cpos;
                 /*
-                 * If the refcount rec already exist, cool. We just need
-                 * to check whether there is a split. Otherwise we just need
-                 * to increase the refcount.
-                 * If we will insert one, increases recs_add.
-                 *
                  * We record all the records which will be inserted to the
                  * same refcount block, so that we can tell exactly whether
                  * we need a new refcount block or not.
+                 *
+                 * If we will insert a new one, this is easy and only happens
+                 * during adding refcounted flag to the extent, so we don't
+                 * have a chance of spliting. We just need one record.
+                 *
+                 * If the refcount rec already exists, that would be a little
+                 * complicated. we may have to:
+                 * 1) split at the beginning if the start pos isn't aligned.
+                 *    we need 1 more record in this case.
+                 * 2) split int the end if the end pos isn't aligned.
+                 *    we need 1 more record in this case.
+                 * 3) split in the middle because of file system fragmentation.
+                 *    we need 2 more records in this case(we can't detect this
+                 *    beforehand, so always think of the worst case).
                  */
                 if (rec.r_refcount) {
+                        recs_add += 2;
                         /* Check whether we need a split at the beginning. */
                         if (cpos == start_cpos &&
                             cpos != le64_to_cpu(rec.r_cpos))