Re: [PATCH 1/3] block: add blk_mq_enter_no_io() and blk_mq_exit_no_io()

[Ming Lei <ming.lei@redhat.com>]

On Wed, Apr 02, 2025 at 12:38:47PM +0800, Ming Lei wrote:
> Add blk_mq_enter_no_io() and blk_mq_exit_no_io() for preventing queue
> from handling any FS or passthrough IO, meantime the queue is kept in
> non-freeze state.
> 
> The added two APIs are for avoiding many potential lock risk related
> with freeze lock.
> 
> Also add two variants of memsave version.
> 
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  block/blk-core.c       |  6 ++++--
>  block/blk-mq.c         | 18 ++++++++++++++++--
>  block/blk-mq.h         | 19 +++++++++++++++++++
>  block/blk.h            |  5 +++--
>  include/linux/blkdev.h |  8 ++++++++
>  5 files changed, 50 insertions(+), 6 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 4623de79effa..a54a18fada8a 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -319,7 +319,8 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
>  		smp_rmb();
>  		wait_event(q->mq_freeze_wq,
>  			   (!q->mq_freeze_depth &&
> -			    blk_pm_resume_queue(pm, q)) ||
> +			    (blk_pm_resume_queue(pm, q) ||
> +			     !blk_queue_no_io(q))) ||
>  			   blk_queue_dying(q));
>  		if (blk_queue_dying(q))
>  			return -ENODEV;
> @@ -352,7 +353,8 @@ int __bio_queue_enter(struct request_queue *q, struct bio *bio)
>  		smp_rmb();
>  		wait_event(q->mq_freeze_wq,
>  			   (!q->mq_freeze_depth &&
> -			    blk_pm_resume_queue(false, q)) ||
> +			    (blk_pm_resume_queue(false, q) ||

Here the above '||' should have been '&&'.

> +			     !blk_queue_no_io(q))) ||
>  			   test_bit(GD_DEAD, &disk->state));
>  		if (test_bit(GD_DEAD, &disk->state))
>  			goto dead;
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index ae8494d88897..075ee51066b3 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -222,8 +222,7 @@ bool __blk_mq_unfreeze_queue(struct request_queue *q, bool force_atomic)
>  	bool unfreeze;
>  
>  	mutex_lock(&q->mq_freeze_lock);
> -	if (force_atomic)
> -		q->q_usage_counter.data->force_atomic = true;
> +	q->q_usage_counter.data->force_atomic = force_atomic;
>  	q->mq_freeze_depth--;
>  	WARN_ON_ONCE(q->mq_freeze_depth < 0);
>  	if (!q->mq_freeze_depth) {
> @@ -278,6 +277,21 @@ void blk_mq_quiesce_queue_nowait(struct request_queue *q)
>  }
>  EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait);
>  
> +void blk_mq_enter_no_io(struct request_queue *q)
> +{
> +	blk_mq_freeze_queue_nomemsave(q);
> +	q->no_io = true;
> +	if (__blk_mq_unfreeze_queue(q, true))
> +		blk_unfreeze_release_lock(q);
> +}
> +
> +void blk_mq_exit_no_io(struct request_queue *q)
> +{
> +	blk_mq_freeze_queue_nomemsave(q);
> +	q->no_io = false;
> +	blk_mq_unfreeze_queue_nomemrestore(q);
> +}
> +
>  /**
>   * blk_mq_wait_quiesce_done() - wait until in-progress quiesce is done
>   * @set: tag_set to wait on
> diff --git a/block/blk-mq.h b/block/blk-mq.h
> index 3011a78cf16a..f49070c8c05f 100644
> --- a/block/blk-mq.h
> +++ b/block/blk-mq.h
> @@ -452,4 +452,23 @@ static inline bool blk_mq_can_poll(struct request_queue *q)
>  		q->tag_set->map[HCTX_TYPE_POLL].nr_queues;
>  }
>  
> +void blk_mq_enter_no_io(struct request_queue *q);
> +void blk_mq_exit_no_io(struct request_queue *q);
> +
> +static inline unsigned int __must_check
> +blk_mq_enter_no_io_memsave(struct request_queue *q)
> +{
> +	unsigned int memflags = memalloc_noio_save();
> +
> +	blk_mq_enter_no_io(q);
> +	return memflags;
> +}
> +
> +static inline void
> +blk_mq_exit_no_io_memrestore(struct request_queue *q, unsigned int memflags)
> +{
> +	blk_mq_exit_no_io(q);
> +	memalloc_noio_restore(memflags);
> +}
> +
>  #endif
> diff --git a/block/blk.h b/block/blk.h
> index 006e3be433d2..7d0994c1d3ad 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -56,8 +56,9 @@ static inline bool blk_try_enter_queue(struct request_queue *q, bool pm)
>  	 * The code that increments the pm_only counter must ensure that the
>  	 * counter is globally visible before the queue is unfrozen.
>  	 */
> -	if (blk_queue_pm_only(q) &&
> -	    (!pm || queue_rpm_status(q) == RPM_SUSPENDED))
> +	if ((blk_queue_pm_only(q) &&
> +	    (!pm || queue_rpm_status(q) == RPM_SUSPENDED)) ||

Same with above.


Thanks, 
Ming