dm thin metadata: Fix ABBA deadlock by resetting dm_bufio_client

As described in commit 8111964f1b85 ("dm thin: Fix ABBA deadlock between
shrink_slab and dm_pool_abort_metadata"), ABBA deadlocks will be
triggered because shrinker_rwsem currently needs to held by
dm_pool_abort_metadata() as a side-effect of thin-pool metadata
operation failure.

The following three problem scenarios have been noticed:

1) Described by commit 8111964f1b85 ("dm thin: Fix ABBA deadlock between
shrink_slab and dm_pool_abort_metadata")

2) shrinker_rwsem and throttle->lock
P1(drop cache) P2(kworker)
drop_caches_sysctl_handler
drop_slab
shrink_slab
down_read(&shrinker_rwsem) - LOCK A
do_shrink_slab
super_cache_scan
prune_icache_sb
dispose_list
evict
ext4_evict_inode
ext4_clear_inode
ext4_discard_preallocations
ext4_mb_load_buddy_gfp
ext4_mb_init_cache
ext4_wait_block_bitmap
__ext4_error
ext4_handle_error
ext4_commit_super
...
dm_submit_bio
do_worker
throttle_work_update
down_write(&t->lock) -- LOCK B
process_deferred_bios
commit
metadata_operation_failed
dm_pool_abort_metadata
dm_block_manager_create
dm_bufio_client_create
register_shrinker
down_write(&shrinker_rwsem)
-- LOCK A
thin_map
thin_bio_map
thin_defer_bio_with_throttle
throttle_lock
down_read(&t->lock) - LOCK B

3) shrinker_rwsem and wait_on_buffer
P1(drop cache) P2(kworker)
drop_caches_sysctl_handler
drop_slab
shrink_slab
down_read(&shrinker_rwsem) - LOCK A
do_shrink_slab
...
ext4_wait_block_bitmap
__ext4_error
ext4_handle_error
jbd2_journal_abort
jbd2_journal_update_sb_errno
jbd2_write_superblock
submit_bh
// LOCK B
// RELEASE B
do_worker
throttle_work_update
down_write(&t->lock) - LOCK B
process_deferred_bios
process_bio
commit
metadata_operation_failed
dm_pool_abort_metadata
dm_block_manager_create
dm_bufio_client_create
register_shrinker
register_shrinker_prepared
down_write(&shrinker_rwsem) - LOCK A
bio_endio
wait_on_buffer
__wait_on_buffer

Fix these by resetting dm_bufio_client without holding shrinker_rwsem.

Fixes: 8111964f1b85 ("dm thin: Fix ABBA deadlock between shrink_slab and dm_pool_abort_metadata")
Cc: [e-mail]
Signed-off-by: Li Lingfeng <[e-mail]>
Signed-off-by: Mike Snitzer <[e-mail]>

drivers/md/dm-bufio.c

···
 }
 EXPORT_SYMBOL_GPL(dm_bufio_client_destroy);
 
+void dm_bufio_client_reset(struct dm_bufio_client *c)
+{
+	drop_buffers(c);
+	flush_work(&c->shrink_work);
+}
+EXPORT_SYMBOL_GPL(dm_bufio_client_reset);
+
 void dm_bufio_set_sector_offset(struct dm_bufio_client *c, sector_t start)
 {
 	c->start = start;

drivers/md/dm-thin-metadata.c

···
 	r = dm_tm_create_with_sm(pmd->bm, THIN_SUPERBLOCK_LOCATION,
 				 &pmd->tm, &pmd->metadata_sm);
 	if (r < 0) {
+		pmd->tm = NULL;
+		pmd->metadata_sm = NULL;
 		DMERR("tm_create_with_sm failed");
 		return r;
 	}
···
 	if (IS_ERR(pmd->data_sm)) {
 		DMERR("sm_disk_create failed");
 		r = PTR_ERR(pmd->data_sm);
+		pmd->data_sm = NULL;
 		goto bad_cleanup_tm;
 	}
 
···
 
 bad_cleanup_nb_tm:
 	dm_tm_destroy(pmd->nb_tm);
+	pmd->nb_tm = NULL;
 bad_cleanup_data_sm:
 	dm_sm_destroy(pmd->data_sm);
+	pmd->data_sm = NULL;
 bad_cleanup_tm:
 	dm_tm_destroy(pmd->tm);
+	pmd->tm = NULL;
 	dm_sm_destroy(pmd->metadata_sm);
+	pmd->metadata_sm = NULL;
 
 	return r;
 }
···
 			       sizeof(disk_super->metadata_space_map_root),
 			       &pmd->tm, &pmd->metadata_sm);
 	if (r < 0) {
+		pmd->tm = NULL;
+		pmd->metadata_sm = NULL;
 		DMERR("tm_open_with_sm failed");
 		goto bad_unlock_sblock;
 	}
···
 	if (IS_ERR(pmd->data_sm)) {
 		DMERR("sm_disk_open failed");
 		r = PTR_ERR(pmd->data_sm);
+		pmd->data_sm = NULL;
 		goto bad_cleanup_tm;
 	}
 
···
 
 bad_cleanup_data_sm:
 	dm_sm_destroy(pmd->data_sm);
+	pmd->data_sm = NULL;
 bad_cleanup_tm:
 	dm_tm_destroy(pmd->tm);
+	pmd->tm = NULL;
 	dm_sm_destroy(pmd->metadata_sm);
+	pmd->metadata_sm = NULL;
 bad_unlock_sblock:
 	dm_bm_unlock(sblock);
 
···
 					      bool destroy_bm)
 {
 	dm_sm_destroy(pmd->data_sm);
+	pmd->data_sm = NULL;
 	dm_sm_destroy(pmd->metadata_sm);
+	pmd->metadata_sm = NULL;
 	dm_tm_destroy(pmd->nb_tm);
+	pmd->nb_tm = NULL;
 	dm_tm_destroy(pmd->tm);
+	pmd->tm = NULL;
 	if (destroy_bm)
 		dm_block_manager_destroy(pmd->bm);
 }
···
 			       __func__, r);
 	}
 	pmd_write_unlock(pmd);
-	if (!pmd->fail_io)
-		__destroy_persistent_data_objects(pmd, true);
+	__destroy_persistent_data_objects(pmd, true);
 
 	kfree(pmd);
 	return 0;
···
 int dm_pool_abort_metadata(struct dm_pool_metadata *pmd)
 {
 	int r = -EINVAL;
-	struct dm_block_manager *old_bm = NULL, *new_bm = NULL;
 
 	/* fail_io is double-checked with pmd->root_lock held below */
 	if (unlikely(pmd->fail_io))
 		return r;
 
-	/*
-	 * Replacement block manager (new_bm) is created and old_bm destroyed outside of
-	 * pmd root_lock to avoid ABBA deadlock that would result (due to life-cycle of
-	 * shrinker associated with the block manager's bufio client vs pmd root_lock).
-	 * - must take shrinker_mutex without holding pmd->root_lock
-	 */
-	new_bm = dm_block_manager_create(pmd->bdev, THIN_METADATA_BLOCK_SIZE << SECTOR_SHIFT,
-					 THIN_MAX_CONCURRENT_LOCKS);
-
 	pmd_write_lock(pmd);
 	if (pmd->fail_io) {
 		pmd_write_unlock(pmd);
-		goto out;
+		return r;
 	}
-
 	__set_abort_with_changes_flags(pmd);
-	__destroy_persistent_data_objects(pmd, false);
-	old_bm = pmd->bm;
-	if (IS_ERR(new_bm)) {
-		DMERR("could not create block manager during abort");
-		pmd->bm = NULL;
-		r = PTR_ERR(new_bm);
-		goto out_unlock;
-	}
 
-	pmd->bm = new_bm;
+	/* destroy data_sm/metadata_sm/nb_tm/tm */
+	__destroy_persistent_data_objects(pmd, false);
+
+	/* reset bm */
+	dm_block_manager_reset(pmd->bm);
+
+	/* rebuild data_sm/metadata_sm/nb_tm/tm */
 	r = __open_or_format_metadata(pmd, false);
-	if (r) {
-		pmd->bm = NULL;
-		goto out_unlock;
-	}
-	new_bm = NULL;
-out_unlock:
 	if (r)
 		pmd->fail_io = true;
 	pmd_write_unlock(pmd);
-	dm_block_manager_destroy(old_bm);
-out:
-	if (new_bm && !IS_ERR(new_bm))
-		dm_block_manager_destroy(new_bm);
-
 	return r;
 }
 

drivers/md/persistent-data/dm-block-manager.c

···
 }
 EXPORT_SYMBOL_GPL(dm_block_manager_destroy);
 
+void dm_block_manager_reset(struct dm_block_manager *bm)
+{
+	dm_bufio_client_reset(bm->bufio);
+}
+EXPORT_SYMBOL_GPL(dm_block_manager_reset);
+
 unsigned int dm_bm_block_size(struct dm_block_manager *bm)
 {
 	return dm_bufio_get_block_size(bm->bufio);

drivers/md/persistent-data/dm-block-manager.h

···
 	struct block_device *bdev, unsigned int block_size,
 	unsigned int max_held_per_thread);
 void dm_block_manager_destroy(struct dm_block_manager *bm);
+void dm_block_manager_reset(struct dm_block_manager *bm);
 
 unsigned int dm_bm_block_size(struct dm_block_manager *bm);
 dm_block_t dm_bm_nr_blocks(struct dm_block_manager *bm);

drivers/md/persistent-data/dm-space-map.h

···
 
 static inline void dm_sm_destroy(struct dm_space_map *sm)
 {
-	sm->destroy(sm);
+	if (sm)
+		sm->destroy(sm);
 }
 
 static inline int dm_sm_extend(struct dm_space_map *sm, dm_block_t extra_blocks)

drivers/md/persistent-data/dm-transaction-manager.c

···
 
 void dm_tm_destroy(struct dm_transaction_manager *tm)
 {
+	if (!tm)
+		return;
+
 	if (!tm->is_clone)
 		wipe_shadow_table(tm);
 

include/linux/dm-bufio.h

···
  */
 void dm_bufio_client_destroy(struct dm_bufio_client *c);
 
+void dm_bufio_client_reset(struct dm_bufio_client *c);
+
 /*
  * Set the sector range.
  * When this function is called, there must be no I/O in progress on the bufio