On 2020-05-16 08:34, Christoph Hellwig wrote:
> No need for two queue references. Also reduce the q_usage_counter
> critical section to just the actual request allocation.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> block/blk-mq.c | 14 ++++----------
> 1 file changed, 4 insertions(+), 10 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index d96d3931f33e6..69e58cc4244c0 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -439,26 +439,20 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
> if (hctx_idx >= q->nr_hw_queues)
> return ERR_PTR(-EIO);
>
> - ret = blk_queue_enter(q, flags);
> - if (ret)
> - return ERR_PTR(ret);
> -
> /*
> * Check if the hardware context is actually mapped to anything.
> * If not tell the caller that it should skip this queue.
> */
> alloc_data.hctx = q->queue_hw_ctx[hctx_idx];
> - if (!blk_mq_hw_queue_mapped(alloc_data.hctx)) {
> - blk_queue_exit(q);
> + if (!blk_mq_hw_queue_mapped(alloc_data.hctx))
> return ERR_PTR(-EXDEV);
> - }
> cpu = cpumask_first_and(alloc_data.hctx->cpumask, cpu_online_mask);
> alloc_data.ctx = __blk_mq_get_ctx(q, cpu);
>
> - blk_queue_enter_live(q);
> + ret = blk_queue_enter(q, flags);
> + if (ret)
> + return ERR_PTR(ret);
> rq = blk_mq_get_request(q, NULL, &alloc_data);
> - blk_queue_exit(q);
> -
> if (!rq) {
> blk_queue_exit(q);
> return ERR_PTR(-EWOULDBLOCK);
This change looks wrong to me. blk_mq_update_nr_hw_queues() modifies
q->queue_hw_ctx so q_usage_counter must be incremented before that
pointer is dereferenced.
Bart.
