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 <redacted>
Signed-off-by: Changheun Lee <redacted>
Signed-off-by: Junho Kim <redacted>
---
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