Merge branch 'for-linus' of git://git.kernel.dk/linux-block

Pull core block fix from Jens Axboe:
 "Jan reported a problem this morning with a crash in blk-mq, and after
  looking over the recent changes, it's obvious that the blk-mq-tag
  waitqueue handling change is buggy.  We could end up _not_ doing
  finish_wait() before switching to a new waitqueue, thus corrupting the
  wait task list"

* 'for-linus' of git://git.kernel.dk/linux-block:
  Revert "blk-mq: Micro-optimize bt_get()"

block/blk-mq-tag.c

@@ -248,8 +248,8 @@ static int bt_get(struct blk_mq_alloc_data *data,
 	if (!(data->gfp & __GFP_WAIT))
 		return -1;
 
+	bs = bt_wait_ptr(bt, hctx);
 	do {
-		bs = bt_wait_ptr(bt, hctx);
 		prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);
 
 		tag = __bt_get(hctx, bt, last_tag);
@@ -285,6 +285,8 @@ static int bt_get(struct blk_mq_alloc_data *data,
 			hctx = data->hctx;
 			bt = &hctx->tags->bitmap_tags;
 		}
+		finish_wait(&bs->wait, &wait);
+		bs = bt_wait_ptr(bt, hctx);
 	} while (1);
 
 	finish_wait(&bs->wait, &wait);