2 files changed, 25 insertions, 9 deletions

diff --git a/fs/xfs/xfs_quota.h b/fs/xfs/xfs_quota.h
index c3483bab9cde..40d508be9a00 100644
--- a/fs/xfs/xfs_quota.h
+++ b/fs/xfs/xfs_quota.h
@@ -108,11 +108,28 @@ typedef struct xfs_dqblk {
         { XFS_DQ_FREEING,       "FREEING" }
 
 /*
- * In the worst case, when both user and group quotas are on,
- * we can have a max of three dquots changing in a single transaction.
+ * We have the possibility of all three quota types being active at once, and
+ * hence free space modification requires modification of all three current
+ * dquots in a single transaction. For this case we need to have a reservation
+ * of at least 3 dquots.
+ *
+ * However, a chmod operation can change both UID and GID in a single
+ * transaction, resulting in requiring {old, new} x {uid, gid} dquots to be
+ * modified. Hence for this case we need to reserve space for at least 4 dquots.
+ *
+ * And in the worst case, there's a rename operation that can be modifying up to
+ * 4 inodes with dquots attached to them. In reality, the only inodes that can
+ * have their dquots modified are the source and destination directory inodes
+ * due to directory name creation and removal. That can require space allocation
+ * and/or freeing on both directory inodes, and hence all three dquots on each
+ * inode can be modified. And if the directories are world writeable, all the
+ * dquots can be unique and so 6 dquots can be modified....
+ *
+ * And, of course, we also need to take into account the dquot log format item
+ * used to describe each dquot.
  */
-#define XFS_DQUOT_LOGRES(mp)    (sizeof(xfs_disk_dquot_t) * 3)
-
+#define XFS_DQUOT_LOGRES(mp)    \
+        ((sizeof(struct xfs_dq_logformat) + sizeof(struct xfs_disk_dquot)) * 6)
 
 /*
  * These are the structures used to lay out dquots and quotaoff
diff --git a/fs/xfs/xfs_trans_dquot.c b/fs/xfs/xfs_trans_dquot.c
index 3ba64d540168..db041a5e1f6d 100644
--- a/fs/xfs/xfs_trans_dquot.c
+++ b/fs/xfs/xfs_trans_dquot.c
@@ -291,11 +291,10 @@ xfs_trans_mod_dquot(
 
 
 /*
- * Given an array of dqtrx structures, lock all the dquots associated
- * and join them to the transaction, provided they have been modified.
- * We know that the highest number of dquots (of one type - usr OR grp),
- * involved in a transaction is 2 and that both usr and grp combined - 3.
- * So, we don't attempt to make this very generic.
+ * Given an array of dqtrx structures, lock all the dquots associated and join
+ * them to the transaction, provided they have been modified.  We know that the
+ * highest number of dquots of one type - usr, grp OR prj - involved in a
+ * transaction is 2 so we don't need to make this very generic.
  */
 STATIC void
 xfs_trans_dqlockedjoin(