It would be really helpful if the commit log contained the explanation
from your reply on the previous submission..
On Tue, Feb 25, 2020 at 09:04:32AM +0800, Ming Lei wrote:
> For some reason, device may be in one situation which can't handle
> FS request, so STS_RESOURCE is always returned and the FS request
> will be added to hctx->dispatch. However passthrough request may
> be required at that time for fixing the problem. If passthrough
> request is added to scheduler queue, there isn't any chance for
> blk-mq to dispatch it given we prioritize requests in hctx->dispatch.
> Then the FS IO request may never be completed, and IO hang is caused.
>
> So passthrough request has to be added to hctx->dispatch directly
> for fixing the IO hang.
>
> Fix this issue by inserting passthrough request into hctx->dispatch
> directly together withing adding FS request to the tail of
> hctx->dispatch in blk_mq_dispatch_rq_list(). Actually we add FS request
> to tail of hctx->dispatch at default, see blk_mq_request_bypass_insert().
>
> Then it becomes consistent with original legacy IO request
> path, in which passthrough request is always added to q->queue_head.
>
> Cc: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: Ewan D. Milne <emilne@xxxxxxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> V2:
> - adding FS request to the tail of hctx->dispatch in blk_mq_dispatch_rq_list()
> - pass our(RH) customer's test
>
> block/blk-flush.c | 2 +-
> block/blk-mq-sched.c | 22 +++++++++++++++-------
> block/blk-mq.c | 18 +++++++++++-------
> block/blk-mq.h | 3 ++-
> 4 files changed, 29 insertions(+), 16 deletions(-)
>
> diff --git a/block/blk-flush.c b/block/blk-flush.c
> index 3f977c517960..5cc775bdb06a 100644
> --- a/block/blk-flush.c
> +++ b/block/blk-flush.c
> @@ -412,7 +412,7 @@ void blk_insert_flush(struct request *rq)
> */
> if ((policy & REQ_FSEQ_DATA) &&
> !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
> - blk_mq_request_bypass_insert(rq, false);
> + blk_mq_request_bypass_insert(rq, false, false);
> return;
> }
>
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index ca22afd47b3d..856356b1619e 100644
> --- a/block/blk-mq-sched.c
> +++ b/block/blk-mq-sched.c
> @@ -361,13 +361,19 @@ static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
> bool has_sched,
> struct request *rq)
> {
> - /* dispatch flush rq directly */
> - if (rq->rq_flags & RQF_FLUSH_SEQ) {
> - spin_lock(&hctx->lock);
> - list_add(&rq->queuelist, &hctx->dispatch);
> - spin_unlock(&hctx->lock);
> + /*
> + * dispatch flush and passthrough rq directly
> + *
> + * passthrough request has to be added to hctx->dispatch directly.
> + * For some reason, device may be in one situation which can't
> + * handle FS request, so STS_RESOURCE is always returned and the
> + * FS request will be added to hctx->dispatch. However passthrough
> + * request may be required at that time for fixing the problem. If
> + * passthrough request is added to scheduler queue, there isn't any
> + * chance to dispatch it given we prioritize requests in hctx->dispatch.
> + */
> + if ((rq->rq_flags & RQF_FLUSH_SEQ) || blk_rq_is_passthrough(rq))
> return true;
> - }
>
> if (has_sched)
> rq->rq_flags |= RQF_SORTED;
> @@ -391,8 +397,10 @@ void blk_mq_sched_insert_request(struct request *rq, bool at_head,
>
> WARN_ON(e && (rq->tag != -1));
>
> - if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
> + if (blk_mq_sched_bypass_insert(hctx, !!e, rq)) {
> + blk_mq_request_bypass_insert(rq, at_head, false);
> goto run;
> + }
>
> if (e && e->type->ops.insert_requests) {
> LIST_HEAD(list);
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index a12b1763508d..5e1e4151cb51 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -735,7 +735,7 @@ static void blk_mq_requeue_work(struct work_struct *work)
> * merge.
> */
> if (rq->rq_flags & RQF_DONTPREP)
> - blk_mq_request_bypass_insert(rq, false);
> + blk_mq_request_bypass_insert(rq, false, false);
> else
> blk_mq_sched_insert_request(rq, true, false, false);
> }
> @@ -1286,7 +1286,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
> q->mq_ops->commit_rqs(hctx);
>
> spin_lock(&hctx->lock);
> - list_splice_init(list, &hctx->dispatch);
> + list_splice_tail_init(list, &hctx->dispatch);
> spin_unlock(&hctx->lock);
>
> /*
> @@ -1677,12 +1677,16 @@ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
> * Should only be used carefully, when the caller knows we want to
> * bypass a potential IO scheduler on the target device.
> */
> -void blk_mq_request_bypass_insert(struct request *rq, bool run_queue)
> +void blk_mq_request_bypass_insert(struct request *rq, bool at_head,
> + bool run_queue)
> {
> struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
>
> spin_lock(&hctx->lock);
> - list_add_tail(&rq->queuelist, &hctx->dispatch);
> + if (at_head)
> + list_add(&rq->queuelist, &hctx->dispatch);
> + else
> + list_add_tail(&rq->queuelist, &hctx->dispatch);
> spin_unlock(&hctx->lock);
>
> if (run_queue)
> @@ -1849,7 +1853,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
> if (bypass_insert)
> return BLK_STS_RESOURCE;
>
> - blk_mq_request_bypass_insert(rq, run_queue);
> + blk_mq_request_bypass_insert(rq, false, run_queue);
> return BLK_STS_OK;
> }
>
> @@ -1876,7 +1880,7 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
>
> ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false, true);
> if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
> - blk_mq_request_bypass_insert(rq, true);
> + blk_mq_request_bypass_insert(rq, false, true);
> else if (ret != BLK_STS_OK)
> blk_mq_end_request(rq, ret);
>
> @@ -1910,7 +1914,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
> if (ret != BLK_STS_OK) {
> if (ret == BLK_STS_RESOURCE ||
> ret == BLK_STS_DEV_RESOURCE) {
> - blk_mq_request_bypass_insert(rq,
> + blk_mq_request_bypass_insert(rq, false,
> list_empty(list));
> break;
> }
> diff --git a/block/blk-mq.h b/block/blk-mq.h
> index eaaca8fc1c28..c0fa34378eb2 100644
> --- a/block/blk-mq.h
> +++ b/block/blk-mq.h
> @@ -66,7 +66,8 @@ int blk_mq_alloc_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
> */
> void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
> bool at_head);
> -void blk_mq_request_bypass_insert(struct request *rq, bool run_queue);
> +void blk_mq_request_bypass_insert(struct request *rq, bool at_head,
> + bool run_queue);
> void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
> struct list_head *list);
>
> --
> 2.20.1
>
---end quoted text---
