linux-kernel - Re: [PATCH 8/8] fs/aio: Use rcu_work instead of explicit rcu and work item

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Message-ID: <20180327155506.GA2779604@devbig577.frc2.facebook.com>
Date:   Tue, 27 Mar 2018 08:55:06 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     torvalds@...ux-foundation.org, jannh@...gle.com,
        paulmck@...ux.vnet.ibm.com, bcrl@...ck.org,
        viro@...iv.linux.org.uk, kent.overstreet@...il.com,
        security@...nel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 8/8] fs/aio: Use rcu_work instead of explicit rcu and
 work item

Hey,

On Tue, Mar 27, 2018 at 04:28:48PM +0200, Oleg Nesterov wrote:
> > flush_*work() guarantees to wait for the completion of the latest
> > instance of the work item which was visible to the caller.  We can't
> > guarantee that w/o rcu_barrier().
> 
> And this is what I can't understand.
> 
> So let me repeat. Could you please describe a use-case which needs flush_rcuwork()
> with rcu_barrier() ?

So, if you skip that, flush_work() in itself won't wait for PENDING
bit at all.  It'll return right away if the work item is waiting for
rcu grace period.

Thanks.

-- 
tejun