1 files changed, 18 insertions, 1 deletions

diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
index ebc4a49801bd..9e8ed607173b 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -119,6 +119,18 @@ struct ocfs2_lock_res_ops {
         void (*post_unlock)(struct ocfs2_super *, struct ocfs2_lock_res *);
 
         /*
+         * Allow a lock type to add checks to determine whether it is
+         * safe to downconvert a lock. Return 0 to re-queue the
+         * downconvert at a later time, nonzero to continue.
+         *
+         * For most locks, the default checks that there are no
+         * incompatible holders are sufficient.
+         *
+         * Called with the lockres spinlock held.
+         */
+        int (*check_downconvert)(struct ocfs2_lock_res *, int);
+
+        /*
          * LOCK_TYPE_* flags which describe the specific requirements
          * of a lock type. Descriptions of each individual flag follow.
          */
@@ -2657,6 +2669,12 @@ recheck:
             && (lockres->l_flags & OCFS2_LOCK_REFRESHING))
                 goto leave_requeue;
 
+        new_level = ocfs2_highest_compat_lock_level(lockres->l_blocking);
+
+        if (lockres->l_ops->check_downconvert
+            && !lockres->l_ops->check_downconvert(lockres, new_level))
+                goto leave_requeue;
+
         /* If we get here, then we know that there are no more
          * incompatible holders (and anyone asking for an incompatible
          * lock is blocked). We can now downconvert the lock */
@@ -2684,7 +2702,6 @@ recheck:
 
 downconvert:
         ctl->requeue = 0;
-        new_level = ocfs2_highest_compat_lock_level(lockres->l_blocking);
 
         ocfs2_prepare_downconvert(lockres, new_level);
         spin_unlock_irqrestore(&lockres->l_lock, flags);