Commit a59db676 authored by Joe Thornber's avatar Joe Thornber Committed by Mike Snitzer
Browse files

dm cache: fix problematic dual use of a single migration count variable 



Introduce a new variable to count the number of allocated migration
structures.  The existing variable cache->nr_migrations became
overloaded.  It was used to:

 i) track of the number of migrations in flight for the purposes of
    quiescing during suspend.

 ii) to estimate the amount of background IO occuring.

Recent discard changes meant that REQ_DISCARD bios are processed with
a migration.  Discards are not background IO so nr_migrations was not
incremented.  However this could cause quiescing to complete early.

(i) is now handled with a new variable cache->nr_allocated_migrations.
cache->nr_migrations has been renamed cache->nr_io_migrations.
cleanup_migration() is now called free_io_migration(), since it
decrements that variable.

Also, remove the unused cache->next_migration variable that got replaced
with with prealloc_structs a while ago.

Signed-off-by: default avatarJoe Thornber <ejt@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
parent 9b1cc9f2

drivers/md/dm-cache-target.c

+50 −39
Original line number Diff line number Diff line
@@ -221,7 +221,13 @@ struct cache { 
	struct list_head need_commit_migrations;

	sector_t migration_threshold;

	wait_queue_head_t migration_wait;

	atomic_t nr_migrations;

	atomic_t nr_allocated_migrations;



	/*

	 * The number of in flight migrations that are performing

	 * background io. eg, promotion, writeback.

	 */

	atomic_t nr_io_migrations;



	wait_queue_head_t quiescing_wait;

	atomic_t quiescing;
@@ -258,7 +264,6 @@ struct cache { 
	struct dm_deferred_set *all_io_ds;



	mempool_t *migration_pool;

	struct dm_cache_migration *next_migration;



	struct dm_cache_policy *policy;

	unsigned policy_nr_args;
@@ -350,10 +355,31 @@ static void free_prison_cell(struct cache *cache, struct dm_bio_prison_cell *cel 
	dm_bio_prison_free_cell(cache->prison, cell);

}



static struct dm_cache_migration *alloc_migration(struct cache *cache)

{

	struct dm_cache_migration *mg;



	mg = mempool_alloc(cache->migration_pool, GFP_NOWAIT);

	if (mg) {

		mg->cache = cache;

		atomic_inc(&mg->cache->nr_allocated_migrations);

	}



	return mg;

}



static void free_migration(struct dm_cache_migration *mg)

{

	if (atomic_dec_and_test(&mg->cache->nr_allocated_migrations))

		wake_up(&mg->cache->migration_wait);



	mempool_free(mg, mg->cache->migration_pool);

}



static int prealloc_data_structs(struct cache *cache, struct prealloc *p)

{

	if (!p->mg) {

		p->mg = mempool_alloc(cache->migration_pool, GFP_NOWAIT);

		p->mg = alloc_migration(cache);

		if (!p->mg)

			return -ENOMEM;

	}
@@ -382,7 +408,7 @@ static void prealloc_free_structs(struct cache *cache, struct prealloc *p) 
		free_prison_cell(cache, p->cell1);



	if (p->mg)

		mempool_free(p->mg, cache->migration_pool);

		free_migration(p->mg);

}



static struct dm_cache_migration *prealloc_get_migration(struct prealloc *p)
@@ -854,24 +880,14 @@ static void remap_to_origin_then_cache(struct cache *cache, struct bio *bio, 
 * Migration covers moving data from the origin device to the cache, or

 * vice versa.

 *--------------------------------------------------------------*/

static void free_migration(struct dm_cache_migration *mg)

{

	mempool_free(mg, mg->cache->migration_pool);

}



static void inc_nr_migrations(struct cache *cache)

static void inc_io_migrations(struct cache *cache)

{

	atomic_inc(&cache->nr_migrations);

	atomic_inc(&cache->nr_io_migrations);

}



static void dec_nr_migrations(struct cache *cache)

static void dec_io_migrations(struct cache *cache)

{

	atomic_dec(&cache->nr_migrations);



	/*

	 * Wake the worker in case we're suspending the target.

	 */

	wake_up(&cache->migration_wait);

	atomic_dec(&cache->nr_io_migrations);

}



static void __cell_defer(struct cache *cache, struct dm_bio_prison_cell *cell,
@@ -894,11 +910,10 @@ static void cell_defer(struct cache *cache, struct dm_bio_prison_cell *cell, 
	wake_worker(cache);

}



static void cleanup_migration(struct dm_cache_migration *mg)

static void free_io_migration(struct dm_cache_migration *mg)

{

	struct cache *cache = mg->cache;

	dec_io_migrations(mg->cache);

	free_migration(mg);

	dec_nr_migrations(cache);

}



static void migration_failure(struct dm_cache_migration *mg)
@@ -923,7 +938,7 @@ static void migration_failure(struct dm_cache_migration *mg) 
		cell_defer(cache, mg->new_ocell, true);

	}



	cleanup_migration(mg);

	free_io_migration(mg);

}



static void migration_success_pre_commit(struct dm_cache_migration *mg)
@@ -934,7 +949,7 @@ static void migration_success_pre_commit(struct dm_cache_migration *mg) 
	if (mg->writeback) {

		clear_dirty(cache, mg->old_oblock, mg->cblock);

		cell_defer(cache, mg->old_ocell, false);

		cleanup_migration(mg);

		free_io_migration(mg);

		return;



	} else if (mg->demote) {
@@ -944,14 +959,14 @@ static void migration_success_pre_commit(struct dm_cache_migration *mg) 
					     mg->old_oblock);

			if (mg->promote)

				cell_defer(cache, mg->new_ocell, true);

			cleanup_migration(mg);

			free_io_migration(mg);

			return;

		}

	} else {

		if (dm_cache_insert_mapping(cache->cmd, mg->cblock, mg->new_oblock)) {

			DMWARN_LIMIT("promotion failed; couldn't update on disk metadata");

			policy_remove_mapping(cache->policy, mg->new_oblock);

			cleanup_migration(mg);

			free_io_migration(mg);

			return;

		}

	}
@@ -984,7 +999,7 @@ static void migration_success_post_commit(struct dm_cache_migration *mg) 
		} else {

			if (mg->invalidate)

				policy_remove_mapping(cache->policy, mg->old_oblock);

			cleanup_migration(mg);

			free_io_migration(mg);

		}



	} else {
@@ -999,7 +1014,7 @@ static void migration_success_post_commit(struct dm_cache_migration *mg) 
			bio_endio(mg->new_ocell->holder, 0);

			cell_defer(cache, mg->new_ocell, false);

		}

		cleanup_migration(mg);

		free_io_migration(mg);

	}

}
@@ -1251,7 +1266,7 @@ static void promote(struct cache *cache, struct prealloc *structs, 
	mg->new_ocell = cell;

	mg->start_jiffies = jiffies;



	inc_nr_migrations(cache);

	inc_io_migrations(cache);

	quiesce_migration(mg);

}
@@ -1275,7 +1290,7 @@ static void writeback(struct cache *cache, struct prealloc *structs, 
	mg->new_ocell = NULL;

	mg->start_jiffies = jiffies;



	inc_nr_migrations(cache);

	inc_io_migrations(cache);

	quiesce_migration(mg);

}
@@ -1302,7 +1317,7 @@ static void demote_then_promote(struct cache *cache, struct prealloc *structs, 
	mg->new_ocell = new_ocell;

	mg->start_jiffies = jiffies;



	inc_nr_migrations(cache);

	inc_io_migrations(cache);

	quiesce_migration(mg);

}
@@ -1330,7 +1345,7 @@ static void invalidate(struct cache *cache, struct prealloc *structs, 
	mg->new_ocell = NULL;

	mg->start_jiffies = jiffies;



	inc_nr_migrations(cache);

	inc_io_migrations(cache);

	quiesce_migration(mg);

}
@@ -1412,7 +1427,7 @@ static void process_discard_bio(struct cache *cache, struct prealloc *structs, 


static bool spare_migration_bandwidth(struct cache *cache)

{

	sector_t current_volume = (atomic_read(&cache->nr_migrations) + 1) *

	sector_t current_volume = (atomic_read(&cache->nr_io_migrations) + 1) *

		cache->sectors_per_block;

	return current_volume < cache->migration_threshold;

}
@@ -1764,7 +1779,7 @@ static void stop_quiescing(struct cache *cache) 


static void wait_for_migrations(struct cache *cache)

{

	wait_event(cache->migration_wait, !atomic_read(&cache->nr_migrations));

	wait_event(cache->migration_wait, !atomic_read(&cache->nr_allocated_migrations));

}



static void stop_worker(struct cache *cache)
@@ -1876,9 +1891,6 @@ static void destroy(struct cache *cache) 
{

	unsigned i;



	if (cache->next_migration)

		mempool_free(cache->next_migration, cache->migration_pool);



	if (cache->migration_pool)

		mempool_destroy(cache->migration_pool);
@@ -2424,7 +2436,8 @@ static int cache_create(struct cache_args *ca, struct cache **result) 
	INIT_LIST_HEAD(&cache->quiesced_migrations);

	INIT_LIST_HEAD(&cache->completed_migrations);

	INIT_LIST_HEAD(&cache->need_commit_migrations);

	atomic_set(&cache->nr_migrations, 0);

	atomic_set(&cache->nr_allocated_migrations, 0);

	atomic_set(&cache->nr_io_migrations, 0);

	init_waitqueue_head(&cache->migration_wait);



	init_waitqueue_head(&cache->quiescing_wait);
@@ -2487,8 +2500,6 @@ static int cache_create(struct cache_args *ca, struct cache **result) 
		goto bad;

	}



	cache->next_migration = NULL;



	cache->need_tick_bio = true;

	cache->sized = false;

	cache->invalidate = false;

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