Revert "blk-mq: Micro-optimize bt_get()"

This reverts commit 52f7eb945f2ba62b324bb9ae16d945326a961dcf.

The optimization is only really safe for a single queue, otherwise
'bs' and 'bt' can indeed change, and if we don't do a finish_wait()
for each loop, we'll potentially change the wait structure and
corrupt task wait list.

Reported-by: Jan Kara <jack@suse.cz>

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index e3d4e40..32e8dbb 100644 (file)
--- a/block/blk-mq-tag.c
+++ b/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);