raid5-ppl: use a single mempool for ppl_io_unit and header_page

Allocate both struct ppl_io_unit and its header_page from a shared
mempool to avoid a possible deadlock. Implement allocate and free
functions for the mempool, remove the second pool for allocating
header_page. The header_pages are now freed with their io_units, not
when the ppl bio completes. Also, use GFP_NOWAIT instead of GFP_ATOMIC
for allocating ppl_io_unit because we can handle failed allocations and
there is no reason to utilize emergency reserves.

Suggested-by: NeilBrown <neilb@suse.com>
Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/raid5-ppl.c

@@ -102,7 +102,6 @@ struct ppl_conf {
 	struct kmem_cache *io_kc;
 	mempool_t *io_pool;
 	struct bio_set *bs;
-	mempool_t *meta_pool;
 
 	/* used only for recovery */
 	int recovered_entries;
@@ -197,25 +196,55 @@ ops_run_partial_parity(struct stripe_head *sh, struct raid5_percpu *percpu,
 	return tx;
 }
 
+static void *ppl_io_pool_alloc(gfp_t gfp_mask, void *pool_data)
+{
+	struct kmem_cache *kc = pool_data;
+	struct ppl_io_unit *io;
+
+	io = kmem_cache_alloc(kc, gfp_mask);
+	if (!io)
+		return NULL;
+
+	io->header_page = alloc_page(gfp_mask);
+	if (!io->header_page) {
+		kmem_cache_free(kc, io);
+		return NULL;
+	}
+
+	return io;
+}
+
+static void ppl_io_pool_free(void *element, void *pool_data)
+{
+	struct kmem_cache *kc = pool_data;
+	struct ppl_io_unit *io = element;
+
+	__free_page(io->header_page);
+	kmem_cache_free(kc, io);
+}
+
 static struct ppl_io_unit *ppl_new_iounit(struct ppl_log *log,
 					  struct stripe_head *sh)
 {
 	struct ppl_conf *ppl_conf = log->ppl_conf;
 	struct ppl_io_unit *io;
 	struct ppl_header *pplhdr;
+	struct page *header_page;
 
-	io = mempool_alloc(ppl_conf->io_pool, GFP_ATOMIC);
+	io = mempool_alloc(ppl_conf->io_pool, GFP_NOWAIT);
 	if (!io)
 		return NULL;
 
+	header_page = io->header_page;
 	memset(io, 0, sizeof(*io));
+	io->header_page = header_page;
+
 	io->log = log;
 	INIT_LIST_HEAD(&io->log_sibling);
 	INIT_LIST_HEAD(&io->stripe_list);
 	atomic_set(&io->pending_stripes, 0);
 	bio_init(&io->bio, io->biovec, PPL_IO_INLINE_BVECS);
 
-	io->header_page = mempool_alloc(ppl_conf->meta_pool, GFP_NOIO);
 	pplhdr = page_address(io->header_page);
 	clear_page(pplhdr);
 	memset(pplhdr->reserved, 0xff, PPL_HDR_RESERVED);
@@ -371,8 +400,6 @@ static void ppl_log_endio(struct bio *bio)
 	if (bio->bi_error)
 		md_error(ppl_conf->mddev, log->rdev);
 
-	mempool_free(io->header_page, ppl_conf->meta_pool);
-
 	list_for_each_entry_safe(sh, next, &io->stripe_list, log_list) {
 		list_del_init(&sh->log_list);
 
@@ -1007,7 +1034,6 @@ static void __ppl_exit_log(struct ppl_conf *ppl_conf)
 
 	kfree(ppl_conf->child_logs);
 
-	mempool_destroy(ppl_conf->meta_pool);
 	if (ppl_conf->bs)
 		bioset_free(ppl_conf->bs);
 	mempool_destroy(ppl_conf->io_pool);
@@ -1113,25 +1139,20 @@ int ppl_init_log(struct r5conf *conf)
 
 	ppl_conf->io_kc = KMEM_CACHE(ppl_io_unit, 0);
 	if (!ppl_conf->io_kc) {
-		ret = -EINVAL;
+		ret = -ENOMEM;
 		goto err;
 	}
 
-	ppl_conf->io_pool = mempool_create_slab_pool(conf->raid_disks, ppl_conf->io_kc);
+	ppl_conf->io_pool = mempool_create(conf->raid_disks, ppl_io_pool_alloc,
+					   ppl_io_pool_free, ppl_conf->io_kc);
 	if (!ppl_conf->io_pool) {
-		ret = -EINVAL;
+		ret = -ENOMEM;
 		goto err;
 	}
 
 	ppl_conf->bs = bioset_create(conf->raid_disks, 0);
 	if (!ppl_conf->bs) {
-		ret = -EINVAL;
-		goto err;
-	}
-
-	ppl_conf->meta_pool = mempool_create_page_pool(conf->raid_disks, 0);
-	if (!ppl_conf->meta_pool) {
-		ret = -EINVAL;
+		ret = -ENOMEM;
 		goto err;
 	}