dm-cache: fix warnings about duplicate slab caches

The commit 4c39529663b9 adds a warning about duplicate cache names if
CONFIG_DEBUG_VM is selected. These warnings are triggered by the dm-cache
code.

The dm-cache code allocates a slab cache for each device. This commit
changes it to allocate just one slab cache in the module init function.

Signed-off-by: Mikulas Patocka <[e-mail]>
Fixes: 4c39529663b9 ("slab: Warn on duplicate cache names when DEBUG_VM=y")

drivers/md/dm-cache-background-tracker.c

···
 
 #define DM_MSG_PREFIX "dm-background-tracker"
 
-struct bt_work {
-	struct list_head list;
-	struct rb_node node;
-	struct policy_work work;
-};
-
 struct background_tracker {
 	unsigned int max_work;
 	atomic_t pending_promotes;
···
 	struct list_head issued;
 	struct list_head queued;
 	struct rb_root pending;
-
-	struct kmem_cache *work_cache;
 };
+
+struct kmem_cache *btracker_work_cache = NULL;
 
 struct background_tracker *btracker_create(unsigned int max_work)
 {
···
 	INIT_LIST_HEAD(&b->queued);
 
 	b->pending = RB_ROOT;
-	b->work_cache = KMEM_CACHE(bt_work, 0);
-	if (!b->work_cache) {
-		DMERR("couldn't create mempool for background work items");
-		kfree(b);
-		b = NULL;
-	}
 
 	return b;
 }
···
 	BUG_ON(!list_empty(&b->issued));
 	list_for_each_entry_safe (w, tmp, &b->queued, list) {
 		list_del(&w->list);
-		kmem_cache_free(b->work_cache, w);
+		kmem_cache_free(btracker_work_cache, w);
 	}
 
-	kmem_cache_destroy(b->work_cache);
 	kfree(b);
 }
 EXPORT_SYMBOL_GPL(btracker_destroy);
···
 	if (max_work_reached(b))
 		return NULL;
 
-	return kmem_cache_alloc(b->work_cache, GFP_NOWAIT);
+	return kmem_cache_alloc(btracker_work_cache, GFP_NOWAIT);
 }
 
 int btracker_queue(struct background_tracker *b,
···
 		 * There was a race, we'll just ignore this second
 		 * bit of work for the same oblock.
 		 */
-		kmem_cache_free(b->work_cache, w);
+		kmem_cache_free(btracker_work_cache, w);
 		return -EINVAL;
 	}
 
···
 	update_stats(b, &w->work, -1);
 	rb_erase(&w->node, &b->pending);
 	list_del(&w->list);
-	kmem_cache_free(b->work_cache, w);
+	kmem_cache_free(btracker_work_cache, w);
 }
 EXPORT_SYMBOL_GPL(btracker_complete);
 

drivers/md/dm-cache-background-tracker.h

···
  * protected with a spinlock.
  */
 
+struct bt_work {
+	struct list_head list;
+	struct rb_node node;
+	struct policy_work work;
+};
+
+extern struct kmem_cache *btracker_work_cache;
+
 struct background_work;
 struct background_tracker;
 

drivers/md/dm-cache-target.c

···
 #include "dm-bio-record.h"
 #include "dm-cache-metadata.h"
 #include "dm-io-tracker.h"
+#include "dm-cache-background-tracker.h"
 
 #include <linux/dm-io.h>
 #include <linux/dm-kcopyd.h>
···
 
 /*----------------------------------------------------------------*/
 
-static struct kmem_cache *migration_cache;
+static struct kmem_cache *migration_cache = NULL;
 
 #define NOT_CORE_OPTION 1
 
···
 	int r;
 
 	migration_cache = KMEM_CACHE(dm_cache_migration, 0);
-	if (!migration_cache)
-		return -ENOMEM;
+	if (!migration_cache) {
+		r = -ENOMEM;
+		goto err;
+	}
+
+	btracker_work_cache = kmem_cache_create("dm_cache_bt_work",
+		sizeof(struct bt_work), __alignof__(struct bt_work), 0, NULL);
+	if (!btracker_work_cache) {
+		r = -ENOMEM;
+		goto err;
+	}
 
 	r = dm_register_target(&cache_target);
 	if (r) {
-		kmem_cache_destroy(migration_cache);
-		return r;
+		goto err;
 	}
 
 	return 0;
+
+err:
+	kmem_cache_destroy(migration_cache);
+	kmem_cache_destroy(btracker_work_cache);
+	return r;
 }
 
 static void __exit dm_cache_exit(void)
 {
 	dm_unregister_target(&cache_target);
 	kmem_cache_destroy(migration_cache);
+	kmem_cache_destroy(btracker_work_cache);
 }
 
 module_init(dm_cache_init);