linux-kernel - [PATCH V4 5/5] blk-mq: ensure hctx to be ran on mapped cpu when issue directly

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Date:   Fri,  2 Nov 2018 15:08:56 +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 V4 5/5] blk-mq: ensure hctx to be ran on mapped cpu when issue directly

When issue request directly and the task is migrated out of the
original cpu where it allocates request, hctx could be ran on
the cpu where it is not mapped. To fix this, insert the request
if BLK_MQ_F_BLOCKING is set, check whether the current is mapped
to the hctx and invoke __blk_mq_issue_directly under preemption
disabled.

Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
---
 block/blk-mq.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index bf8b144..4450eb6 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1771,6 +1771,17 @@ static blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 	enum mq_issue_decision dec;
 	int srcu_idx;
 
+	if (hctx->flags & BLK_MQ_F_BLOCKING) {
+		force = true;
+		goto out;
+	}
+
+	if (!cpumask_test_cpu(get_cpu(), hctx->cpumask)) {
+		put_cpu();
+		force = true;
+		goto out;
+	}
+
 	hctx_lock(hctx, &srcu_idx);
 
 	/*
@@ -1801,7 +1812,8 @@ static blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 
 out_unlock:
 	hctx_unlock(hctx, srcu_idx);
-
+	put_cpu();
+out:
 	dec = blk_mq_make_dicision(ret, bypass, force);
 	switch(dec) {
 	case MQ_ISSUE_INSERT_QUEUE:
-- 
2.7.4