dm snapshot: use per device mempools

Change snapshot per-module mempool to per-device mempool.

Per-module mempools could cause a deadlock if multiple
snapshot devices are stacked above each other.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

2 files changed, 24 insertions, 18 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index f4fd0cee9c3d..6e5528aecc98 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -96,7 +96,6 @@ 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;
@@ -364,14 +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,
@@ -627,12 +631,18 @@ 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 bad6;
+                goto bad_tracked_chunk_pool;
         }
 
         for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
@@ -669,6 +679,9 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
  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);
 
@@ -723,6 +736,8 @@ static void snapshot_dtr(struct dm_target *ti)
 
         __free_exceptions(s);
 
+        mempool_destroy(s->pending_pool);
+
         dm_put_device(ti, s->origin);
         dm_put_device(ti, s->cow);
 
@@ -969,7 +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) {
@@ -989,7 +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)) {
@@ -1418,24 +1432,15 @@ static int __init dm_snapshot_init(void)
                 goto bad5;
         }
 
-        pending_pool = mempool_create_slab_pool(128, pending_cache);
-        if (!pending_pool) {
-                DMERR("Couldn't create pending pool.");
-                r = -ENOMEM;
-                goto bad_pending_pool;
-        }
-
         ksnapd = create_singlethread_workqueue("ksnapd");
         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:
@@ -1466,7 +1471,6 @@ 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);
diff --git a/drivers/md/dm-snap.h b/drivers/md/dm-snap.h
index 70dc961f40d8..292c15609ae3 100644
--- a/drivers/md/dm-snap.h
+++ b/drivers/md/dm-snap.h
@@ -161,6 +161,8 @@ struct dm_snapshot {
         /* The last percentage we notified */
         int last_percent;
 
+        mempool_t *pending_pool;
+
         struct exception_table pending;
         struct exception_table complete;