| Message ID | 20220726023852.3413784-1-yukuai1@huaweicloud.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | blk-mq: fix io hung due to missing commit_rqs while scheduler is none | expand |
On Tue, Jul 26, 2022 at 10:38:52AM +0800, Yu Kuai wrote: > From: Yu Kuai <yukuai3@huawei.com> > > Currently, in virtio_scsi, if 'bd->last' is not set to true while > dispatching request, such io will stay in driver's queue, and driver > will wait for block layer to dispatch more rqs. However, if block > layer failed to dispatch more rq, it should trigger commit_rqs to > inform driver. > > There is a problem in blk_mq_try_issue_list_directly() that commit_rqs > won't be called: > > // assume that queue_depth is set to 1, list contains two rq > blk_mq_try_issue_list_directly > blk_mq_request_issue_directly > // dispatch first rq > // last is false > __blk_mq_try_issue_directly > blk_mq_get_dispatch_budget > // succeed to get first budget > __blk_mq_issue_directly > scsi_queue_rq > cmd->flags |= SCMD_LAST > virtscsi_queuecommand > kick = (sc->flags & SCMD_LAST) != 0 > // kick is false, first rq won't issue to disk > queued++ > > blk_mq_request_issue_directly > // dispatch second rq > __blk_mq_try_issue_directly > blk_mq_get_dispatch_budget > // failed to get second budget > ret == BLK_STS_RESOURCE > blk_mq_request_bypass_insert > // errors is still 0 > > if (!list_empty(list) || errors && ...) > // won't pass, commit_rqs won't be called > > In this situation, first rq relied on second rq to dispatch, while > second rq relied on first rq to complete, thus they will both hung. > > Fix the problem by also treat 'BLK_STS_RESOURCE' and > 'BLK_STS_DEV_RESOURCE' as 'errors' in blk_mq_try_issue_list_directly(), > so that 'commit_rqs' will be called when dispatch of last rq failed. > > Fixes: d666ba98f849 ("blk-mq: add mq_ops->commit_rqs()") > Signed-off-by: Yu Kuai <yukuai3@huawei.com> > --- > block/blk-mq.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 70177ee74295..752b0fe4c128 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -2680,6 +2680,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx, > list_del_init(&rq->queuelist); > ret = blk_mq_request_issue_directly(rq, list_empty(list)); > if (ret != BLK_STS_OK) { > + errors++; OK, it is because that list becomes empty, but .queue_rq(last_rq_in_list) returns BLK_STS_*RESOURCE, but scsi can't call ->queuecommand() for this real last rq. Then blk_mq_try_issue_list_directly() doesn't call ->commit_rqs() too. Here errors means that request not queued successfully, so this patch looks fine. Also I think blk_mq_dispatch_rq_list() needs similar handling too, right? thanks, Ming
Hi, Ming 在 2022/07/26 10:48, Ming Lei 写道: > On Tue, Jul 26, 2022 at 10:38:52AM +0800, Yu Kuai wrote: >> From: Yu Kuai <yukuai3@huawei.com> >> >> Currently, in virtio_scsi, if 'bd->last' is not set to true while >> dispatching request, such io will stay in driver's queue, and driver >> will wait for block layer to dispatch more rqs. However, if block >> layer failed to dispatch more rq, it should trigger commit_rqs to >> inform driver. >> >> There is a problem in blk_mq_try_issue_list_directly() that commit_rqs >> won't be called: >> >> // assume that queue_depth is set to 1, list contains two rq >> blk_mq_try_issue_list_directly >> blk_mq_request_issue_directly >> // dispatch first rq >> // last is false >> __blk_mq_try_issue_directly >> blk_mq_get_dispatch_budget >> // succeed to get first budget >> __blk_mq_issue_directly >> scsi_queue_rq >> cmd->flags |= SCMD_LAST >> virtscsi_queuecommand >> kick = (sc->flags & SCMD_LAST) != 0 >> // kick is false, first rq won't issue to disk >> queued++ >> >> blk_mq_request_issue_directly >> // dispatch second rq >> __blk_mq_try_issue_directly >> blk_mq_get_dispatch_budget >> // failed to get second budget >> ret == BLK_STS_RESOURCE >> blk_mq_request_bypass_insert >> // errors is still 0 >> >> if (!list_empty(list) || errors && ...) >> // won't pass, commit_rqs won't be called >> >> In this situation, first rq relied on second rq to dispatch, while >> second rq relied on first rq to complete, thus they will both hung. >> >> Fix the problem by also treat 'BLK_STS_RESOURCE' and >> 'BLK_STS_DEV_RESOURCE' as 'errors' in blk_mq_try_issue_list_directly(), >> so that 'commit_rqs' will be called when dispatch of last rq failed. >> >> Fixes: d666ba98f849 ("blk-mq: add mq_ops->commit_rqs()") >> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >> --- >> block/blk-mq.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/block/blk-mq.c b/block/blk-mq.c >> index 70177ee74295..752b0fe4c128 100644 >> --- a/block/blk-mq.c >> +++ b/block/blk-mq.c >> @@ -2680,6 +2680,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx, >> list_del_init(&rq->queuelist); >> ret = blk_mq_request_issue_directly(rq, list_empty(list)); >> if (ret != BLK_STS_OK) { >> + errors++; > > OK, it is because that list becomes empty, but .queue_rq(last_rq_in_list) > returns BLK_STS_*RESOURCE, but scsi can't call ->queuecommand() for this > real last rq. Then blk_mq_try_issue_list_directly() doesn't call > ->commit_rqs() too. > > Here errors means that request not queued successfully, so this patch > looks fine. > > Also I think blk_mq_dispatch_rq_list() needs similar handling too, > right? Yes, you're right, I'll handle blk_mq_dispatch_rq_list() in v2, and also change the title. Thanks, Kuai
diff --git a/block/blk-mq.c b/block/blk-mq.c index 70177ee74295..752b0fe4c128 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2680,6 +2680,7 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx, list_del_init(&rq->queuelist); ret = blk_mq_request_issue_directly(rq, list_empty(list)); if (ret != BLK_STS_OK) { + errors++; if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE) { blk_mq_request_bypass_insert(rq, false, @@ -2687,7 +2688,6 @@ void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx, break; } blk_mq_end_request(rq, ret); - errors++; } else queued++; }