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Date:   Wed, 21 Dec 2022 09:21:31 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     zhangyanjun@cestc.cn
Cc:     sagi@grimberg.me, axboe@kernel.dk, kbusch@kernel.org, axboe@fb.com,
        hch@lst.de, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-block@vger.kernel.org
Subject: Re: [PATCH v2] nvme: fix multipath crash caused by flush request
 when blktrace is enabled
Message-ID: <20221221082131.GA23644@lst.de>
References: <20221220063233.43932-1-zhangyanjun@cestc.cn>
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Just checking for ->bio seems to be:

 - simpler
 - faster

and does not require block layer internals.  So why not just this:


diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 6bbb73ef8b2548..424c8a467a0c2a 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -893,7 +893,7 @@ static inline void nvme_trace_bio_complete(struct request *req)
 {
 	struct nvme_ns *ns = req->q->queuedata;
 
-	if (req->cmd_flags & REQ_NVME_MPATH)
+	if ((req->cmd_flags & REQ_NVME_MPATH) && req->bio)
 		trace_block_bio_complete(ns->head->disk->queue, req->bio);
 }