bcache: avoid flushing btree node in cache_set_flush() if io disabled

When cache_set_flush() is called for too many I/O errors detected on
cache device and the cache set is retiring, inside the function it
doesn't make sense to flushing cached btree nodes from c->btree_cache
because CACHE_SET_IO_DISABLE is set on c->flags already and all I/Os
onto cache device will be rejected.

This patch checks in cache_set_flush() that whether CACHE_SET_IO_DISABLE
is set. If yes, then avoids to flush the cached btree nodes to reduce
more time and make cache set retiring more faster.
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/super.c

@@ -1553,13 +1553,17 @@ static void cache_set_flush(struct closure *cl)
 	if (!IS_ERR_OR_NULL(c->root))
 		list_add(&c->root->list, &c->btree_cache);
 
-	/* Should skip this if we're unregistering because of an error */
-	list_for_each_entry(b, &c->btree_cache, list) {
-		mutex_lock(&b->write_lock);
-		if (btree_node_dirty(b))
-			__bch_btree_node_write(b, NULL);
-		mutex_unlock(&b->write_lock);
-	}
+	/*
+	 * Avoid flushing cached nodes if cache set is retiring
+	 * due to too many I/O errors detected.
+	 */
+	if (!test_bit(CACHE_SET_IO_DISABLE, &c->flags))
+		list_for_each_entry(b, &c->btree_cache, list) {
+			mutex_lock(&b->write_lock);
+			if (btree_node_dirty(b))
+				__bch_btree_node_write(b, NULL);
+			mutex_unlock(&b->write_lock);
+		}
 
 	for_each_cache(ca, c, i)
 		if (ca->alloc_thread)