Re: [PATCH] block: ensure we hold a queue reference when using queue limits

Ming Lei
2024-01-13T02:05:30Z

On Sat, Jan 13, 2024 at 12:15 AM Jens Axboe <axboe@kernel.dk> wrote:
>
> q_usage_counter is the only thing preventing us from the limits changing
> under us in __bio_split_to_limits, but blk_mq_submit_bio doesn't hold
> it while calling into it.
>
> Move the splitting inside the region where we know we've got a queue
> reference. Ideally this could still remain a shared section of code, but
> let's keep the fix simple and defer any refactoring here to later.
>
> Reported-by: Christoph Hellwig <hch@lst.de>
> Fixes: 9d497e2941c3 ("block: don't protect submit_bio_checks by q_usage_counter")

The fixes tag is wrong, and it should be:

Fixes: 900e08075202 ("block: move queue enter logic into blk_mq_submit_bio()")

> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>
> ---
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index f57b86d6de6a..e02c4b1af8c5 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2964,12 +2964,6 @@ void blk_mq_submit_bio(struct bio *bio)
> blk_status_t ret;
>
> bio = blk_queue_bounce(bio, q);
> - if (bio_may_exceed_limits(bio, &q->limits)) {
> - bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
> - if (!bio)
> - return;
> - }
> -
> bio_set_ioprio(bio);
>
> if (plug) {
> @@ -2978,6 +2972,11 @@ void blk_mq_submit_bio(struct bio *bio)
> rq = NULL;
> }
> if (rq) {
> + if (unlikely(bio_may_exceed_limits(bio, &q->limits))) {
> + bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
> + if (!bio)
> + return;
> + }
> if (!bio_integrity_prep(bio))
> return;
> if (blk_mq_attempt_bio_merge(q, bio, nr_segs))
> @@ -2988,6 +2987,11 @@ void blk_mq_submit_bio(struct bio *bio)
> } else {
> if (unlikely(bio_queue_enter(bio)))
> return;
> + if (unlikely(bio_may_exceed_limits(bio, &q->limits))) {
> + bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
> + if (!bio)
> + goto fail;
> + }

With "Fixes" tag fixed, the patch looks fine:

Reviewed-by: Ming Lei <ming.lei@redhat.com>