dm snapshot: fix race during exception creation

[linux-2.6-omap-h63xx.git] / drivers / md / dm-snap.c

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index de302702ab3e23b9dc95b0dee56b786d74a3365e..f4fd0cee9c3d43f1c06ec288af0d7476bf4f4538 100644 (file)
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -134,6 +134,27 @@ static void stop_tracking_chunk(struct dm_snapshot *s,
        mempool_free(c, s->tracked_chunk_pool);
 }
 
+static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk)
+{
+       struct dm_snap_tracked_chunk *c;
+       struct hlist_node *hn;
+       int found = 0;
+
+       spin_lock_irq(&s->tracked_chunk_lock);
+
+       hlist_for_each_entry(c, hn,
+           &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)], node) {
+               if (c->chunk == chunk) {
+                       found = 1;
+                       break;
+               }
+       }
+
+       spin_unlock_irq(&s->tracked_chunk_lock);
+
+       return found;
+}
+
 /*
  * One of these per registered origin, held in the snapshot_origins hash
  */
@@ -839,6 +860,13 @@ static void pending_complete(struct dm_snap_pending_exception *pe, int success)
                goto out;
        }
 
+       /*
+        * Check for conflicting reads. This is extremely improbable,
+        * so yield() is sufficient and there is no need for a wait queue.
+        */
+       while (__chunk_is_tracked(s, pe->e.old_chunk))
+               yield();
+
        /*
         * Add a proper exception, and remove the
         * in-flight exception from the list.