On Fri, Mar 12 2021 at 10:44am -0500,
Sergei Shtepa <sergei.sht...@veeam.com> wrote:
> blk_mq_is_queue_frozen() allow to assert that the queue is frozen.
>
> Signed-off-by: Sergei Shtepa <sergei.sht...@veeam.com>
> ---
> block/blk-mq.c | 13 +++++++++++++
> include/linux/blk-mq.h | 1 +
> 2 files changed, 14 insertions(+)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index d4d7c1caa439..2f188a865024 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -161,6 +161,19 @@ int blk_mq_freeze_queue_wait_timeout(struct
> request_queue *q,
> }
> EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_wait_timeout);
>
> +bool blk_mq_is_queue_frozen(struct request_queue *q)
> +{
> + bool frozen;
> +
> + mutex_lock(&q->mq_freeze_lock);
> + frozen = percpu_ref_is_dying(&q->q_usage_counter) &&
> + percpu_ref_is_zero(&q->q_usage_counter);
> + mutex_unlock(&q->mq_freeze_lock);
> +
> + return frozen;
> +}
> +EXPORT_SYMBOL_GPL(blk_mq_is_queue_frozen);
> +
This is returning a frozen state that is immediately stale. I don't
think any code calling this is providing the guarantees you think it
does due to the racey nature of this state once the mutex is dropped.
> /*
> * Guarantee no request is in use, so we can change any data structure of
> * the queue afterward.
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 2c473c9b8990..6f01971abf7b 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -533,6 +533,7 @@ void blk_freeze_queue_start(struct request_queue *q);
> void blk_mq_freeze_queue_wait(struct request_queue *q);
> int blk_mq_freeze_queue_wait_timeout(struct request_queue *q,
> unsigned long timeout);
> +bool blk_mq_is_queue_frozen(struct request_queue *q);
>
> int blk_mq_map_queues(struct blk_mq_queue_map *qmap);
> void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int
> nr_hw_queues);
> --
> 2.20.1
>
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