1 files changed, 28 insertions, 0 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index de302702ab3e..f4fd0cee9c3d 100644
--- 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
  */
@@ -840,6 +861,13 @@ static void pending_complete(struct dm_snap_pending_exception *pe, int success)
         }
 
         /*
+         * 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.
          */