On 4/15/21 3:33 AM, Ming Lei wrote:
> 1) grab two queue usage refcount for blk-mq before submitting blk-mq
> bio, one is for bio, anther is for request;
^^^^^^
another?
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 09f774e7413d..f71e4b433030 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -431,12 +431,13 @@ EXPORT_SYMBOL(blk_cleanup_queue);
> int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
> {
> const bool pm = flags & BLK_MQ_REQ_PM;
> + const unsigned int nr = (flags & BLK_MQ_REQ_DOUBLE_REF) ? 2 : 1;
Please leave out the parentheses from around the condition in the above
and in other ternary expressions. The ternary operator has a very low
precedence so adding parentheses around the condition in a ternary
operator is almost never necessary.
> @@ -480,8 +481,18 @@ static inline int bio_queue_enter(struct bio *bio)
> struct request_queue *q = bio->bi_bdev->bd_disk->queue;
> bool nowait = bio->bi_opf & REQ_NOWAIT;
> int ret;
> + blk_mq_req_flags_t flags = nowait ? BLK_MQ_REQ_NOWAIT : 0;
> + bool reffed = bio_flagged(bio, BIO_QUEUE_REFFED);
>
> - ret = blk_queue_enter(q, nowait ? BLK_MQ_REQ_NOWAIT : 0);
> + if (!reffed)
> + bio_set_flag(bio, BIO_QUEUE_REFFED);
> +
> + /*
> + * Grab two queue references for blk-mq, one is for bio, and
> + * another is for blk-mq request.
> + */
> + ret = blk_queue_enter(q, q->mq_ops && !reffed ?
> + (flags | BLK_MQ_REQ_DOUBLE_REF) : flags);
Consider rewriting the above code as follows to make it easier to read:
if (q->mq_ops && !reffed)
flags |= BLK_MQ_REQ_DOUBLE_REF;
ret = blk_queue_enter(q, flags);
Please also expand the comment above this code. The comment only
explains the reffed == false case but not the reffed == true case. I
assume that the reffed == true case applies to stacked bio-based drivers?
Thanks,
Bart.
