On 2020-04-16 04:18, John Garry wrote:
> If in blk_mq_dispatch_rq_list() we find no budget, then we break of the
> dispatch loop, but the request may keep the driver tag, evaulated
> in 'nxt' in the previous loop iteration.
>
> Fix by putting the driver tag for that request.
>
> Signed-off-by: John Garry <john.garry@xxxxxxxxxx>
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 8e56884fd2e9..a7785df2c944 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1222,8 +1222,10 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
> rq = list_first_entry(list, struct request, queuelist);
>
> hctx = rq->mq_hctx;
> - if (!got_budget && !blk_mq_get_dispatch_budget(hctx))
> + if (!got_budget && !blk_mq_get_dispatch_budget(hctx)) {
> + blk_mq_put_driver_tag(rq);
> break;
> + }
>
> if (!blk_mq_get_driver_tag(rq)) {
> /*
Is this something that can only happen if q->mq_ops->queue_rq(hctx, &bd)
returns another value than BLK_STS_OK, BLK_STS_RESOURCE and
BLK_STS_DEV_RESOURCE? If so, please add a comment in the source code
that explains this.
Is this perhaps a bug fix for 0bca799b9280 ("blk-mq: order getting
budget and driver tag")? If so, please mention this and add Cc tags for
the people who were Cc-ed on that patch.
Thanks,
Bart.
