Re: [RFC PATCH 2/7] blk-mq: add blk-mq flag of BLK_MQ_F_NO_MANAGED_IRQ

[John Garry <john.garry@huawei.com>]

在 12/07/2019 10:47, Ming Lei 写道:
> We will stop hw queue and wait for completion of in-flight requests
> when one hctx is becoming dead in the following patch. This way may
> cause dead-lock for some stacking blk-mq drivers, such as dm-rq and
> loop.
> 
> Add blk-mq flag of BLK_MQ_F_NO_MANAGED_IRQ and mark it for dm-rq and
> loop, so we needn't to wait for completion of in-flight requests of
> dm-rq & loop, then the potential dead-lock can be avoided.

Wouldn't it make more sense to have the flag name be like 
BLK_MQ_F_DONT_DRAIN_STOPPED_HCTX?

I did not think that blk-mq is specifically concerned with managed 
interrupts, but only their indirect effect.

> 
> Cc: Bart Van Assche <bvanassche@acm.org>
> Cc: Hannes Reinecke <hare@suse.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Keith Busch <keith.busch@intel.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>   block/blk-mq-debugfs.c | 1 +
>   drivers/block/loop.c   | 2 +-
>   drivers/md/dm-rq.c     | 2 +-
>   include/linux/blk-mq.h | 1 +
>   4 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
> index af40a02c46ee..24fff8c90942 100644
> --- a/block/blk-mq-debugfs.c
> +++ b/block/blk-mq-debugfs.c
> @@ -240,6 +240,7 @@ static const char *const hctx_flag_name[] = {
>   	HCTX_FLAG_NAME(TAG_SHARED),
>   	HCTX_FLAG_NAME(BLOCKING),
>   	HCTX_FLAG_NAME(NO_SCHED),
> +	HCTX_FLAG_NAME(NO_MANAGED_IRQ),
>   };
>   #undef HCTX_FLAG_NAME
>   
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 44c9985f352a..199d76e8bf46 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1986,7 +1986,7 @@ static int loop_add(struct loop_device **l, int i)
>   	lo->tag_set.queue_depth = 128;
>   	lo->tag_set.numa_node = NUMA_NO_NODE;
>   	lo->tag_set.cmd_size = sizeof(struct loop_cmd);
> -	lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
> +	lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_NO_MANAGED_IRQ;

nit: at this point in the series you're setting a flag which is never 
checked.

>   	lo->tag_set.driver_data = lo;
>   
>   	err = blk_mq_alloc_tag_set(&lo->tag_set);
> diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
> index 5f7063f05ae0..f7fbef2d3cd7 100644
> --- a/drivers/md/dm-rq.c
> +++ b/drivers/md/dm-rq.c
> @@ -546,7 +546,7 @@ int dm_mq_init_request_queue(struct mapped_device *md, struct dm_table *t)
>   	md->tag_set->ops = &dm_mq_ops;
>   	md->tag_set->queue_depth = dm_get_blk_mq_queue_depth();
>   	md->tag_set->numa_node = md->numa_node_id;
> -	md->tag_set->flags = BLK_MQ_F_SHOULD_MERGE;
> +	md->tag_set->flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_NO_MANAGED_IRQ;
>   	md->tag_set->nr_hw_queues = dm_get_blk_mq_nr_hw_queues();
>   	md->tag_set->driver_data = md;
>   
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 3a731c3c0762..911cdc6479dc 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -219,6 +219,7 @@ struct blk_mq_ops {
>   enum {
>   	BLK_MQ_F_SHOULD_MERGE	= 1 << 0,
>   	BLK_MQ_F_TAG_SHARED	= 1 << 1,
> +	BLK_MQ_F_NO_MANAGED_IRQ	= 1 << 2,
>   	BLK_MQ_F_BLOCKING	= 1 << 5,
>   	BLK_MQ_F_NO_SCHED	= 1 << 6,
>   	BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
>