linux-kernel - Re: [PATCH 1/7] blk-mq: protect completion path with RCU

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Message-ID: <20180108171234.GX3668920@devbig577.frc2.facebook.com>
Date:   Mon, 8 Jan 2018 09:12:34 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     jack@...e.cz, axboe@...nel.dk, clm@...com, jbacik@...com,
        kernel-team@...com, linux-kernel@...r.kernel.org,
        linux-btrfs@...r.kernel.org, peterz@...radead.org,
        jianchao.w.wang@...cle.com, Bart.VanAssche@....com
Subject: Re: [PATCH 1/7] blk-mq: protect completion path with RCU

Hello, Christoph.

On Fri, Dec 29, 2017 at 02:04:18AM -0800, Christoph Hellwig wrote:
> Why do you need the srcu protection?  The completion path can never
> sleep.
> 
> If there is a good reason to keep it please add commment, and
> make the srcu variant a separate function only used by drivers that
> need it instead of adding the conditional.

It's either that or adding protection against both srcu and rcu in the
counterpart.  It's easier / cleaner to just use single rcu construct
for a given queue.  Will add a comment.  Jens already has a patch
which factors out the conditionals.

Thanks.

-- 
tejun