linux-kernel - [PATCH 1/1] blk-mq: added case for cpu offline during send_ipi in rq

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Message-Id: <20220826013136.16763-1-mj0123.lee@samsung.com>
Date:   Fri, 26 Aug 2022 10:31:36 +0900
From:   Manjong Lee <mj0123.lee@...sung.com>
To:     mj0123.lee@...sung.com, axboe@...nel.dk,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     seunghwan.hyun@...sung.com, sookwan7.kim@...sung.com,
        nanich.lee@...sung.com, yt0928.kim@...sung.com,
        junho89.kim@...sung.com, jisoo2146.oh@...sung.com,
        sbeom16.kim@...sung.com
Subject: [PATCH 1/1] blk-mq: added case for cpu offline during send_ipi in
 rq_complete

When a request complete then send ipi to original cpu which issued request.
If cpu offline during this process, send_ipi might fail.
However, there is currently no code to handle this error case.
This may cause in missing request complete.
Therefore, if send_ipi fails due to cpu offline, the request complete
has to be processed directly from the cpu where it is running.

Signed-off-by: Manjong Lee <mj0123.lee@...sung.com>
Signed-off-by: Changheun Lee <nanich.lee@...sung.com>
Signed-off-by: Junho Kim <junho89.kim@...sung.com>
---
 block/blk-mq.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3c1e6b6d991d..f2ce79708c5e 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1064,17 +1064,22 @@ static inline bool blk_mq_complete_need_ipi(struct request *rq)
 	return cpu_online(rq->mq_ctx->cpu);
 }
 
-static void blk_mq_complete_send_ipi(struct request *rq)
+static int blk_mq_complete_send_ipi(struct request *rq)
 {
 	struct llist_head *list;
 	unsigned int cpu;
+	int ret = 0;
 
 	cpu = rq->mq_ctx->cpu;
 	list = &per_cpu(blk_cpu_done, cpu);
 	if (llist_add(&rq->ipi_list, list)) {
 		INIT_CSD(&rq->csd, __blk_mq_complete_request_remote, rq);
-		smp_call_function_single_async(cpu, &rq->csd);
+		ret = smp_call_function_single_async(cpu, &rq->csd);
+		if (ret)
+			llist_del_all(list);
 	}
+
+	return ret;
 }
 
 static void blk_mq_raise_softirq(struct request *rq)
@@ -1099,10 +1104,9 @@ bool blk_mq_complete_request_remote(struct request *rq)
 	if (rq->cmd_flags & REQ_POLLED)
 		return false;
 
-	if (blk_mq_complete_need_ipi(rq)) {
-		blk_mq_complete_send_ipi(rq);
-		return true;
-	}
+	if (blk_mq_complete_need_ipi(rq))
+		if (!blk_mq_complete_send_ipi(rq))
+			return true;
 
 	if (rq->q->nr_hw_queues == 1) {
 		blk_mq_raise_softirq(rq);
-- 
2.32.0