dm thin: change data device's flush_bio to be member of struct pool

With commit fe64369163c5 ("dm thin: don't allow changing data device
during thin-pool load") it is now possible to re-parent the data
device's flush_bio from the pool_c to pool structure.  Doing so offers
improved lifetime guarantees for the flush_bio so that the call to
dm_pool_register_pre_commit_callback can now be done safely from
pool_ctr().

Depends-on: fe64369163c5 ("dm thin: don't allow changing data device during thin-pool load")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-thin.c

@@ -282,6 +282,8 @@ struct pool {
 	struct dm_bio_prison_cell **cell_sort_array;
 
 	mempool_t mapping_pool;
+
+	struct bio flush_bio;
 };
 
 static void metadata_operation_failed(struct pool *pool, const char *op, int r);
@@ -329,7 +331,6 @@ struct pool_c {
 	dm_block_t low_water_blocks;
 	struct pool_features requested_pf; /* Features requested during table load */
 	struct pool_features adjusted_pf;  /* Features used after adjusting for constituent devices */
-	struct bio flush_bio;
 };
 
 /*
@@ -2925,6 +2926,7 @@ static void __pool_destroy(struct pool *pool)
 	if (pool->next_mapping)
 		mempool_free(pool->next_mapping, &pool->mapping_pool);
 	mempool_exit(&pool->mapping_pool);
+	bio_uninit(&pool->flush_bio);
 	dm_deferred_set_destroy(pool->shared_read_ds);
 	dm_deferred_set_destroy(pool->all_io_ds);
 	kfree(pool);
@@ -3005,6 +3007,7 @@ static struct pool *pool_create(struct mapped_device *pool_md,
 	pool->low_water_triggered = false;
 	pool->suspended = true;
 	pool->out_of_data_space = false;
+	bio_init(&pool->flush_bio, NULL, 0);
 
 	pool->shared_read_ds = dm_deferred_set_create();
 	if (!pool->shared_read_ds) {
@@ -3132,7 +3135,6 @@ static void pool_dtr(struct dm_target *ti)
 	__pool_dec(pt->pool);
 	dm_put_device(ti, pt->metadata_dev);
 	dm_put_device(ti, pt->data_dev);
-	bio_uninit(&pt->flush_bio);
 	kfree(pt);
 
 	mutex_unlock(&dm_thin_pool_table.mutex);
@@ -3211,11 +3213,11 @@ static void metadata_low_callback(void *context)
  */
 static int metadata_pre_commit_callback(void *context)
 {
-	struct pool_c *pt = context;
-	struct bio *flush_bio = &pt->flush_bio;
+	struct pool *pool = context;
+	struct bio *flush_bio = &pool->flush_bio;
 
 	bio_reset(flush_bio);
-	bio_set_dev(flush_bio, pt->data_dev->bdev);
+	bio_set_dev(flush_bio, pool->data_dev);
 	flush_bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
 
 	return submit_bio_wait(flush_bio);
@@ -3389,7 +3391,6 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
 	pt->data_dev = data_dev;
 	pt->low_water_blocks = low_water_blocks;
 	pt->adjusted_pf = pt->requested_pf = pf;
-	bio_init(&pt->flush_bio, NULL, 0);
 	ti->num_flush_bios = 1;
 
 	/*
@@ -3416,6 +3417,9 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
 	if (r)
 		goto out_flags_changed;
 
+	dm_pool_register_pre_commit_callback(pool->pmd,
+					     metadata_pre_commit_callback, pool);
+
 	pt->callbacks.congested_fn = pool_is_congested;
 	dm_table_add_target_callbacks(ti->table, &pt->callbacks);
 
@@ -3578,9 +3582,6 @@ static int pool_preresume(struct dm_target *ti)
 	if (r)
 		return r;
 
-	dm_pool_register_pre_commit_callback(pool->pmd,
-					     metadata_pre_commit_callback, pt);
-
 	r = maybe_resize_data_dev(ti, &need_commit1);
 	if (r)
 		return r;