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Subject[PATCH] blk-mq: don't dispatch request in blk_mq_request_direct_issue if queue is busy
Date
If we run into blk_mq_request_direct_issue(), when queue is busy, we
don't want to dispatch this request into hctx->dispatch_list, and
what we need to do is to return the queue busy info to caller, so
that caller can deal with it well.

Fixes: 396eaf21ee ("blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback")
Reported-by: Laurence Oberman <loberman@redhat.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-mq.c | 22 ++++++++++------------
1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 4d4af8d712da..1af7fa70993b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1856,15 +1856,6 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
return ret;
}

-static void __blk_mq_fallback_to_insert(struct request *rq,
- bool run_queue, bool bypass_insert)
-{
- if (!bypass_insert)
- blk_mq_sched_insert_request(rq, false, run_queue, false);
- else
- blk_mq_request_bypass_insert(rq, run_queue);
-}
-
static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
struct request *rq,
blk_qc_t *cookie,
@@ -1873,9 +1864,16 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
struct request_queue *q = rq->q;
bool run_queue = true;

- /* RCU or SRCU read lock is needed before checking quiesced flag */
+ /*
+ * RCU or SRCU read lock is needed before checking quiesced flag.
+ *
+ * When queue is stopped or quiesced, ignore 'bypass_insert' from
+ * blk_mq_request_direct_issue(), and return BLK_STS_OK to caller,
+ * and avoid driver to try to dispatch again.
+ */
if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)) {
run_queue = false;
+ bypass_insert = false;
goto insert;
}

@@ -1892,10 +1890,10 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,

return __blk_mq_issue_directly(hctx, rq, cookie);
insert:
- __blk_mq_fallback_to_insert(rq, run_queue, bypass_insert);
if (bypass_insert)
return BLK_STS_RESOURCE;

+ blk_mq_sched_insert_request(rq, false, run_queue, false);
return BLK_STS_OK;
}

@@ -1911,7 +1909,7 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,

ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false);
if (ret == BLK_STS_RESOURCE)
- __blk_mq_fallback_to_insert(rq, true, false);
+ blk_mq_sched_insert_request(rq, false, true, false);
else if (ret != BLK_STS_OK)
blk_mq_end_request(rq, ret);

--
2.9.5
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