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Date:   Wed, 13 May 2020 13:59:32 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        John Garry <john.garry@huawei.com>,
        Bart Van Assche <bvanassche@acm.org>,
        Hannes Reinecke <hare@suse.com>,
        Christoph Hellwig <hch@lst.de>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH V11 07/12] blk-mq: stop to handle IO and drain IO
 before hctx becomes inactive
Message-ID: <20200513115932.GC6297@lst.de>
References: <20200513034803.1844579-1-ming.lei@redhat.com> <20200513034803.1844579-8-ming.lei@redhat.com>
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> +	if (unlikely(direct_issue && rq->mq_ctx->cpu != raw_smp_processor_id()))
> +		smp_mb();
> +	else
> +		barrier();

Independ of the fact that I still think this is horrible and hacky,
I also still don't see what the barrier() is trying to help with.