1 files changed, 141 insertions, 22 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 1ba8a47d61b..6e5528aecc9 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -40,6 +40,11 @@
  */
 #define SNAPSHOT_PAGES (((1UL << 20) >> PAGE_SHIFT) ? : 1)
 
+/*
+ * The size of the mempool used to track chunks in use.
+ */
+#define MIN_IOS 256
+
 static struct workqueue_struct *ksnapd;
 static void flush_queued_bios(struct work_struct *work);
 
@@ -91,7 +96,63 @@ struct dm_snap_pending_exception {
  */
 static struct kmem_cache *exception_cache;
 static struct kmem_cache *pending_cache;
-static mempool_t *pending_pool;
+
+struct dm_snap_tracked_chunk {
+	struct hlist_node node;
+	chunk_t chunk;
+};
+
+static struct kmem_cache *tracked_chunk_cache;
+
+static struct dm_snap_tracked_chunk *track_chunk(struct dm_snapshot *s,
+						 chunk_t chunk)
+{
+	struct dm_snap_tracked_chunk *c = mempool_alloc(s->tracked_chunk_pool,
+							GFP_NOIO);
+	unsigned long flags;
+
+	c->chunk = chunk;
+
+	spin_lock_irqsave(&s->tracked_chunk_lock, flags);
+	hlist_add_head(&c->node,
+		       &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]);
+	spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
+
+	return c;
+}
+
+static void stop_tracking_chunk(struct dm_snapshot *s,
+				struct dm_snap_tracked_chunk *c)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&s->tracked_chunk_lock, flags);
+	hlist_del(&c->node);
+	spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
+
+	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
@@ -302,14 +363,19 @@ static void free_exception(struct dm_snap_exception *e)
 	kmem_cache_free(exception_cache, e);
 }
 
-static struct dm_snap_pending_exception *alloc_pending_exception(void)
+static struct dm_snap_pending_exception *alloc_pending_exception(struct dm_snapshot *s)
 {
-	return mempool_alloc(pending_pool, GFP_NOIO);
+	struct dm_snap_pending_exception *pe = mempool_alloc(s->pending_pool,
+							     GFP_NOIO);
+
+	pe->snap = s;
+
+	return pe;
 }
 
 static void free_pending_exception(struct dm_snap_pending_exception *pe)
 {
-	mempool_free(pe, pending_pool);
+	mempool_free(pe, pe->snap->pending_pool);
 }
 
 static void insert_completed_exception(struct dm_snapshot *s,
@@ -482,6 +548,7 @@ static int set_chunk_size(struct dm_snapshot *s, const char *chunk_size_arg,
 static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 {
 	struct dm_snapshot *s;
+	int i;
 	int r = -EINVAL;
 	char persistent;
 	char *origin_path;
@@ -564,11 +631,30 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		goto bad5;
 	}
 
+	s->pending_pool = mempool_create_slab_pool(MIN_IOS, pending_cache);
+	if (!s->pending_pool) {
+		ti->error = "Could not allocate mempool for pending exceptions";
+		goto bad6;
+	}
+
+	s->tracked_chunk_pool = mempool_create_slab_pool(MIN_IOS,
+							 tracked_chunk_cache);
+	if (!s->tracked_chunk_pool) {
+		ti->error = "Could not allocate tracked_chunk mempool for "
+			    "tracking reads";
+		goto bad_tracked_chunk_pool;
+	}
+
+	for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
+		INIT_HLIST_HEAD(&s->tracked_chunk_hash[i]);
+
+	spin_lock_init(&s->tracked_chunk_lock);
+
 	/* Metadata must only be loaded into one table at once */
 	r = s->store.read_metadata(&s->store);
 	if (r < 0) {
 		ti->error = "Failed to read snapshot metadata";
-		goto bad6;
+		goto bad_load_and_register;
 	} else if (r > 0) {
 		s->valid = 0;
 		DMWARN("Snapshot is marked invalid.");
@@ -582,7 +668,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	if (register_snapshot(s)) {
 		r = -EINVAL;
 		ti->error = "Cannot register snapshot origin";
-		goto bad6;
+		goto bad_load_and_register;
 	}
 
 	ti->private = s;
@@ -590,6 +676,12 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 
 	return 0;
 
+ bad_load_and_register:
+	mempool_destroy(s->tracked_chunk_pool);
+
+ bad_tracked_chunk_pool:
+	mempool_destroy(s->pending_pool);
+
  bad6:
 	dm_kcopyd_client_destroy(s->kcopyd_client);
 
@@ -624,6 +716,9 @@ static void __free_exceptions(struct dm_snapshot *s)
 
 static void snapshot_dtr(struct dm_target *ti)
 {
+#ifdef CONFIG_DM_DEBUG
+	int i;
+#endif
 	struct dm_snapshot *s = ti->private;
 
 	flush_workqueue(ksnapd);
@@ -632,8 +727,17 @@ static void snapshot_dtr(struct dm_target *ti)
 	/* After this returns there can be no new kcopyd jobs. */
 	unregister_snapshot(s);
 
+#ifdef CONFIG_DM_DEBUG
+	for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
+		BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i]));
+#endif
+
+	mempool_destroy(s->tracked_chunk_pool);
+
 	__free_exceptions(s);
 
+	mempool_destroy(s->pending_pool);
+
 	dm_put_device(ti, s->origin);
 	dm_put_device(ti, s->cow);
 
@@ -772,6 +876,13 @@ 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.
 	 */
@@ -873,7 +984,7 @@ __find_pending_exception(struct dm_snapshot *s, struct bio *bio)
 	 * to hold the lock while we do this.
 	 */
 	up_write(&s->lock);
-	pe = alloc_pending_exception();
+	pe = alloc_pending_exception(s);
 	down_write(&s->lock);
 
 	if (!s->valid) {
@@ -893,7 +1004,6 @@ __find_pending_exception(struct dm_snapshot *s, struct bio *bio)
 	bio_list_init(&pe->snapshot_bios);
 	pe->primary_pe = NULL;
 	atomic_set(&pe->ref_count, 0);
-	pe->snap = s;
 	pe->started = 0;
 
 	if (s->store.prepare_exception(&s->store, &pe->e)) {
@@ -974,14 +1084,10 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
 			start_copy(pe);
 			goto out;
 		}
-	} else
-		/*
-		 * FIXME: this read path scares me because we
-		 * always use the origin when we have a pending
-		 * exception.  However I can't think of a
-		 * situation where this is wrong - ejt.
-		 */
+	} else {
 		bio->bi_bdev = s->origin->bdev;
+		map_context->ptr = track_chunk(s, chunk);
+	}
 
  out_unlock:
 	up_write(&s->lock);
@@ -989,6 +1095,18 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
 	return r;
 }
 
+static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
+			   int error, union map_info *map_context)
+{
+	struct dm_snapshot *s = ti->private;
+	struct dm_snap_tracked_chunk *c = map_context->ptr;
+
+	if (c)
+		stop_tracking_chunk(s, c);
+
+	return 0;
+}
+
 static void snapshot_resume(struct dm_target *ti)
 {
 	struct dm_snapshot *s = ti->private;
@@ -1266,6 +1384,7 @@ static struct target_type snapshot_target = {
 	.ctr     = snapshot_ctr,
 	.dtr     = snapshot_dtr,
 	.map     = snapshot_map,
+	.end_io  = snapshot_end_io,
 	.resume  = snapshot_resume,
 	.status  = snapshot_status,
 };
@@ -1306,9 +1425,9 @@ static int __init dm_snapshot_init(void)
 		goto bad4;
 	}
 
-	pending_pool = mempool_create_slab_pool(128, pending_cache);
-	if (!pending_pool) {
-		DMERR("Couldn't create pending pool.");
+	tracked_chunk_cache = KMEM_CACHE(dm_snap_tracked_chunk, 0);
+	if (!tracked_chunk_cache) {
+		DMERR("Couldn't create cache to track chunks in use.");
 		r = -ENOMEM;
 		goto bad5;
 	}
@@ -1317,13 +1436,13 @@ static int __init dm_snapshot_init(void)
 	if (!ksnapd) {
 		DMERR("Failed to create ksnapd workqueue.");
 		r = -ENOMEM;
-		goto bad6;
+		goto bad_pending_pool;
 	}
 
 	return 0;
 
-      bad6:
-	mempool_destroy(pending_pool);
+      bad_pending_pool:
+	kmem_cache_destroy(tracked_chunk_cache);
       bad5:
 	kmem_cache_destroy(pending_cache);
       bad4:
@@ -1352,9 +1471,9 @@ static void __exit dm_snapshot_exit(void)
 		DMERR("origin unregister failed %d", r);
 
 	exit_origin_hash();
-	mempool_destroy(pending_pool);
 	kmem_cache_destroy(pending_cache);
 	kmem_cache_destroy(exception_cache);
+	kmem_cache_destroy(tracked_chunk_cache);
 }
 
 /* Module hooks */