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blk-mq: insert passthrough request into hctx->dispatch directly

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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@oracle.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2020-02-25 09:04:32 +08:00 committed by Jens Axboe
parent f8788d86ab
commit 01e99aeca3
4 changed files with 29 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
block/blk-flush.c
View File

@ -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;
}

22
block/blk-mq-sched.c
View File

@ -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);

18
block/blk-mq.c
View File

@ -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;
}

3
block/blk-mq.h
View File

@ -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);