From 0e87e58bf60edb6bb28e493c7a143f41b091a5e5 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Wed, 24 Aug 2016 15:38:01 -0600
Subject: [PATCH] blk-mq: improve warning for running a queue on the wrong CPU

__blk_mq_run_hw_queue() currently warns if we are running the queue on a
CPU that isn't set in its mask. However, this can happen if a CPU is
being offlined, and the workqueue handling will place the work on CPU0
instead. Improve the warning so that it only triggers if the batch cpu
in the hardware queue is currently online.  If it triggers for that
case, then it's indicative of a flow problem in blk-mq, so we want to
retain it for that case.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 block/blk-mq.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 729169d022fc5..13f5a6c1de768 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -793,11 +793,12 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 	struct list_head *dptr;
 	int queued;
 
-	WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask));
-
 	if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state)))
 		return;
 
+	WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) &&
+		cpu_online(hctx->next_cpu));
+
 	hctx->run++;
 
 	/*
-- 
2.30.2