On Wed, Jun 03, 2020 at 06:51:27PM +0800, Ming Lei wrote:
> Commit bf0beec0607d ("blk-mq: drain I/O when all CPUs in a hctx are offline")
> prevents new request from being allocated on hctx which is going to be inactive,
> meantime drains all in-queue requests.
>
> We needn't to prevent driver tag from being allocated during cpu hotplug, more
> importantly we have to provide driver tag for requests, so that the cpu hotplug
> handling can move on. blk_mq_get_tag() is shared for allocating both internal
> tag and drive tag, so driver tag allocation may fail because the hctx is
> marked as inactive.
>
> Fix the issue by moving BLK_MQ_S_INACTIVE check to __blk_mq_alloc_request().
This looks correct, but a little ugly. How about we resurrect my
patch to split off blk_mq_get_driver_tag entirely? Quick untested rebase
below, still needs a better changelog and fixes tg:
---
>From e432011e2eb5ac7bd1046bbf936645e9f7b74e64 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@xxxxxx>
Date: Sat, 16 May 2020 08:03:48 +0200
Subject: blk-mq: split out a __blk_mq_get_driver_tag helper
Allocation of the driver tag in the case of using a scheduler shares very
little code with the "normal" tag allocation. Split out a new helper to
streamline this path, and untangle it from the complex normal tag
allocation.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
block/blk-mq-tag.c | 27 +++++++++++++++++++++++++++
block/blk-mq-tag.h | 8 ++++++++
block/blk-mq.c | 29 -----------------------------
block/blk-mq.h | 1 -
4 files changed, 35 insertions(+), 30 deletions(-)
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 96a39d0724a29..cded7fdcad8ef 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -191,6 +191,33 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
return tag + tag_offset;
}
+bool __blk_mq_get_driver_tag(struct request *rq)
+{
+ struct sbitmap_queue *bt = &rq->mq_hctx->tags->bitmap_tags;
+ unsigned int tag_offset = rq->mq_hctx->tags->nr_reserved_tags;
+ bool shared = blk_mq_tag_busy(rq->mq_hctx);
+ int tag;
+
+ if (blk_mq_tag_is_reserved(rq->mq_hctx->sched_tags, rq->internal_tag)) {
+ bt = &rq->mq_hctx->tags->breserved_tags;
+ tag_offset = 0;
+ }
+
+ if (!hctx_may_queue(rq->mq_hctx, bt))
+ return false;
+ tag = __sbitmap_queue_get(bt);
+ if (tag == BLK_MQ_NO_TAG)
+ return false;
+
+ rq->tag = tag + tag_offset;
+ if (shared) {
+ rq->rq_flags |= RQF_MQ_INFLIGHT;
+ atomic_inc(&rq->mq_hctx->nr_active);
+ }
+ rq->mq_hctx->tags->rqs[rq->tag] = rq;
+ return true;
+}
+
void blk_mq_put_tag(struct blk_mq_tags *tags, struct blk_mq_ctx *ctx,
unsigned int tag)
{
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index d38e48f2a0a4a..2e4ef51cdb32a 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -51,6 +51,14 @@ enum {
BLK_MQ_TAG_MAX = BLK_MQ_NO_TAG - 1,
};
+bool __blk_mq_get_driver_tag(struct request *rq);
+static inline bool blk_mq_get_driver_tag(struct request *rq)
+{
+ if (rq->tag != BLK_MQ_NO_TAG)
+ return true;
+ return __blk_mq_get_driver_tag(rq);
+}
+
extern bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *);
extern void __blk_mq_tag_idle(struct blk_mq_hw_ctx *);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9a36ac1c1fa1d..4f57d27bfa737 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1052,35 +1052,6 @@ static inline unsigned int queued_to_index(unsigned int queued)
return min(BLK_MQ_MAX_DISPATCH_ORDER - 1, ilog2(queued) + 1);
}
-bool blk_mq_get_driver_tag(struct request *rq)
-{
- struct blk_mq_alloc_data data = {
- .q = rq->q,
- .hctx = rq->mq_hctx,
- .flags = BLK_MQ_REQ_NOWAIT,
- .cmd_flags = rq->cmd_flags,
- };
- bool shared;
-
- if (rq->tag != BLK_MQ_NO_TAG)
- return true;
-
- if (blk_mq_tag_is_reserved(data.hctx->sched_tags, rq->internal_tag))
- data.flags |= BLK_MQ_REQ_RESERVED;
-
- shared = blk_mq_tag_busy(data.hctx);
- rq->tag = blk_mq_get_tag(&data);
- if (rq->tag >= 0) {
- if (shared) {
- rq->rq_flags |= RQF_MQ_INFLIGHT;
- atomic_inc(&data.hctx->nr_active);
- }
- data.hctx->tags->rqs[rq->tag] = rq;
- }
-
- return rq->tag != BLK_MQ_NO_TAG;
-}
-
static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode,
int flags, void *key)
{
diff --git a/block/blk-mq.h b/block/blk-mq.h
index a139b06318174..b3ce0f3a2ad2a 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -44,7 +44,6 @@ bool blk_mq_dispatch_rq_list(struct request_queue *, struct list_head *, bool);
void blk_mq_add_to_requeue_list(struct request *rq, bool at_head,
bool kick_requeue_list);
void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, struct list_head *list);
-bool blk_mq_get_driver_tag(struct request *rq);
struct request *blk_mq_dequeue_from_ctx(struct blk_mq_hw_ctx *hctx,
struct blk_mq_ctx *start);
--
2.26.2
