linux-kernel - [PATCH V9 1/4] blk-mq: insert to hctx dispatch list when bypass

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Message-Id: <1543995842-20704-2-git-send-email-jianchao.w.wang@oracle.com>
Date:   Wed,  5 Dec 2018 15:43:59 +0800
From:   Jianchao Wang <jianchao.w.wang@...cle.com>
To:     axboe@...nel.dk
Cc:     ming.lei@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH V9 1/4] blk-mq: insert to hctx dispatch list when bypass_insert is true

We don't allow direct dispatch of anything but regular reads/writes
and insert all of non-read-write requests. However, this is not
correct for 'bypass_insert == true' case where inserting is ignored
and BLK_STS_RESOURCE is returned. The caller will fail forever.

Fix it with inserting the non-read-write request to hctx dispatch
list to avoid to involve merge and io scheduler when bypass_insert
is true.

Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
---
 block/blk-mq.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9005505..153af90 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1822,6 +1822,7 @@ 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;
+	bool force = false;
 
 	/*
 	 * RCU or SRCU read lock is needed before checking quiesced flag.
@@ -1836,9 +1837,19 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 		goto insert;
 	}
 
-	if (!blk_rq_can_direct_dispatch(rq) || (q->elevator && !bypass_insert))
+	if (q->elevator && !bypass_insert)
 		goto insert;
 
+	if (!blk_rq_can_direct_dispatch(rq)) {
+		/*
+		 * For 'bypass_insert == true' case, insert request into hctx
+		 * dispatch list.
+		 */
+		if (bypass_insert)
+			force = true;
+		goto insert;
+	}
+
 	if (!blk_mq_get_dispatch_budget(hctx))
 		goto insert;
 
@@ -1849,8 +1860,12 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 
 	return __blk_mq_issue_directly(hctx, rq, cookie, last);
 insert:
-	if (bypass_insert)
+	if (force) {
+		blk_mq_request_bypass_insert(rq, run_queue);
+		return BLK_STS_OK;
+	} else if (bypass_insert) {
 		return BLK_STS_RESOURCE;
+	}
 
 	blk_mq_sched_insert_request(rq, false, run_queue, false);
 	return BLK_STS_OK;
-- 
2.7.4