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
