linux-kernel - Re: [PATCH 1/6] blk-mq: protect completion path with RCU

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Message-ID: <20171213161312.GS3919388@devbig577.frc2.facebook.com>
Date:   Wed, 13 Dec 2017 08:13:12 -0800
From:   Tejun Heo <tj@...nel.org>
To:     "jianchao.wang" <jianchao.w.wang@...cle.com>
Cc:     axboe@...nel.dk, linux-kernel@...r.kernel.org, oleg@...hat.com,
        peterz@...radead.org, kernel-team@...com, osandov@...com,
        linux-block@...r.kernel.org, hch@....de
Subject: Re: [PATCH 1/6] blk-mq: protect completion path with RCU

Hello,

On Wed, Dec 13, 2017 at 11:30:48AM +0800, jianchao.wang wrote:
> > +	} else {
> > +		srcu_idx = srcu_read_lock(hctx->queue_rq_srcu);
> > +		if (!blk_mark_rq_complete(rq))
> > +			__blk_mq_complete_request(rq);
> > +		srcu_read_unlock(hctx->queue_rq_srcu, srcu_idx);
> 
> The __blk_mq_complete_request() could be executed in irq context. There should not be any 
> sleeping operations in it. If just synchronize with the timeout path to ensure the aborted_gstate
> to be seen, only rcu is needed here ,as well as the blk_mq_timeout_work.

Sure, but it's just a lot cleaner to use the same to protect both
issue and completion; otherwise, whoever who wants to synchronize
against them have to do awkward double rcu locking.

Thanks.

-- 
tejun