[PATCH 03/47] block: defer timeouts to a workqueue

[Jeff Moyer]

Christoph Hellwig <hch at lst.de> writes:

> Timer context is not very useful for drivers to perform any meaningful abort
> action from.  So instead of calling the driver from this useless context
> defer it to a workqueue as soon as possible.
>
> Note that while a delayed_work item would seem the right thing here I didn't
> dare to use it due to the magic in blk_add_timer that pokes deep into timer
> internals.  But maybe this encourages Tejun to add a sensible API for that to
> the workqueue API and we'll all be fine in the end :)

I don't see where the blk-mq timeout work is ever scheduled.  You
removed the call to setup_timer for the mq case, so what causes the mq
timeout work to run?  I must be missing something.

-Jeff

>
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>  block/blk-core.c       | 8 ++++++++
>  block/blk-mq.c         | 8 +++++---
>  block/blk-timeout.c    | 5 +++--
>  block/blk.h            | 2 +-
>  include/linux/blkdev.h | 1 +
>  5 files changed, 18 insertions(+), 6 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 5131993b..1de0974 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -664,6 +664,13 @@ static void blk_queue_usage_counter_release(struct percpu_ref *ref)
>  	wake_up_all(&q->mq_freeze_wq);
>  }
>  
> +static void blk_rq_timed_out_timer(unsigned long data)
> +{
> +	struct request_queue *q = (struct request_queue *)data;
> +
> +	kblockd_schedule_work(&q->timeout_work);
> +}
> +
>  struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
>  {
>  	struct request_queue *q;
> @@ -825,6 +832,7 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
>  	if (blk_init_rl(&q->root_rl, q, GFP_KERNEL))
>  		goto fail;
>  
> +	INIT_WORK(&q->timeout_work, blk_timeout_work);
>  	q->request_fn		= rfn;
>  	q->prep_rq_fn		= NULL;
>  	q->unprep_rq_fn		= NULL;
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 3ae09de..8354601 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -85,6 +85,7 @@ void blk_mq_freeze_queue_start(struct request_queue *q)
>  	freeze_depth = atomic_inc_return(&q->mq_freeze_depth);
>  	if (freeze_depth == 1) {
>  		percpu_ref_kill(&q->q_usage_counter);
> +		cancel_work_sync(&q->timeout_work);
>  		blk_mq_run_hw_queues(q, false);
>  	}
>  }
> @@ -617,9 +618,10 @@ static void blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
>  	}
>  }
>  
> -static void blk_mq_rq_timer(unsigned long priv)
> +static void blk_mq_timeout_work(struct work_struct *work)
>  {
> -	struct request_queue *q = (struct request_queue *)priv;
> +	struct request_queue *q =
> +		container_of(work, struct request_queue, timeout_work);
>  	struct blk_mq_timeout_data data = {
>  		.next		= 0,
>  		.next_set	= 0,
> @@ -2015,7 +2017,7 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
>  		hctxs[i]->queue_num = i;
>  	}
>  
> -	setup_timer(&q->timeout, blk_mq_rq_timer, (unsigned long) q);
> +	INIT_WORK(&q->timeout_work, blk_mq_timeout_work);
>  	blk_queue_rq_timeout(q, set->timeout ? set->timeout : 30 * HZ);
>  
>  	q->nr_queues = nr_cpu_ids;
> diff --git a/block/blk-timeout.c b/block/blk-timeout.c
> index aa40aa9..aedd128 100644
> --- a/block/blk-timeout.c
> +++ b/block/blk-timeout.c
> @@ -127,9 +127,10 @@ static void blk_rq_check_expired(struct request *rq, unsigned long *next_timeout
>  	}
>  }
>  
> -void blk_rq_timed_out_timer(unsigned long data)
> +void blk_timeout_work(struct work_struct *work)
>  {
> -	struct request_queue *q = (struct request_queue *) data;
> +	struct request_queue *q =
> +		container_of(work, struct request_queue, timeout_work);
>  	unsigned long flags, next = 0;
>  	struct request *rq, *tmp;
>  	int next_set = 0;
> diff --git a/block/blk.h b/block/blk.h
> index da722eb..37b9165 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -95,7 +95,7 @@ static inline void blk_flush_integrity(void)
>  }
>  #endif
>  
> -void blk_rq_timed_out_timer(unsigned long data);
> +void blk_timeout_work(struct work_struct *work);
>  unsigned long blk_rq_timeout(unsigned long timeout);
>  void blk_add_timer(struct request *req);
>  void blk_delete_timer(struct request *);
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 3fe27f8..9a8424a 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -407,6 +407,7 @@ struct request_queue {
>  
>  	unsigned int		rq_timeout;
>  	struct timer_list	timeout;
> +	struct work_struct	timeout_work;
>  	struct list_head	timeout_list;
>  
>  	struct list_head	icq_list;