Re: [PATCH 1/2] blk-mq: not deactivate hctx if the device doesn't use managed irq

Damien Le Moal
2021-06-29T23:30:40Z

On 2021/06/29 16:50, Ming Lei wrote:
> hctx is deactivated when all CPU in hctx->cpumask become offline by
> draining all requests originated from this hctx and moving new
> allocation to active hctx. This way is for avoiding inflight IO when
> the managed irq is shutdown.
>
> Some drivers(nvme fc, rdma, tcp, loop) doesn't use managed irq, so
> they needn't to deactivate hctx. Also, they are the only user of
> blk_mq_alloc_request_hctx() which is used for connecting io queue.
> And their requirement is that the connect request can be submitted
> via one specified hctx on which all CPU in its hctx->cpumask may have
> become offline.
>
> Address the requirement for nvme fc/rdma/loop, so the reported kernel
> panic on the following line in blk_mq_alloc_request_hctx() can be fixed.
>
> data.ctx = __blk_mq_get_ctx(q, cpu)
>
> Cc: Sagi Grimberg <sagi@grimberg.me>
> Cc: Daniel Wagner <dwagner@suse.de>
> Cc: Wen Xiong <wenxiong@us.ibm.com>
> Cc: John Garry <john.garry@huawei.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> block/blk-mq.c | 6 +++++-
> include/linux/blk-mq.h | 1 +
> 2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index df5dc3b756f5..74632f50d969 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -494,7 +494,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
> data.hctx = q->queue_hw_ctx[hctx_idx];
> if (!blk_mq_hw_queue_mapped(data.hctx))
> goto out_queue_exit;
> - cpu = cpumask_first_and(data.hctx->cpumask, cpu_online_mask);
> + cpu = cpumask_first(data.hctx->cpumask);
> data.ctx = __blk_mq_get_ctx(q, cpu);
>
> if (!q->elevator)
> @@ -2570,6 +2570,10 @@ static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
> !blk_mq_last_cpu_in_hctx(cpu, hctx))
> return 0;
>
> + /* Controller doesn't use managed IRQ, no need to deactivate hctx */
> + if (hctx->flags & BLK_MQ_F_NOT_USE_MANAGED_IRQ)
> + return 0;
> +
> /*
> * Prevent new request from being allocated on the current hctx.
> *
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 21140132a30d..600c5dd1a069 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -403,6 +403,7 @@ enum {
> */
> BLK_MQ_F_STACKING = 1 << 2,
> BLK_MQ_F_TAG_HCTX_SHARED = 1 << 3,
> + BLK_MQ_F_NOT_USE_MANAGED_IRQ = 1 << 4,

My 2 cents: BLK_MQ_F_NO_MANAGED_IRQ may be a better/shorter name.

> BLK_MQ_F_BLOCKING = 1 << 5,
> BLK_MQ_F_NO_SCHED = 1 << 6,
> BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
>

--
Damien Le Moal
Western Digital Research