linux-kernel - Re: [PATCH 7/7] RCU, workqueue: Implement rcu

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Message-ID: <20180309162137.GC2943022@devbig577.frc2.facebook.com>
Date:   Fri, 9 Mar 2018 08:21:37 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Lai Jiangshan <jiangshanlai+lkml@...il.com>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        torvalds@...ux-foundation.org, Jann Horn <jannh@...gle.com>,
        bcrl@...ck.org, viro@...iv.linux.org.uk,
        Kent Overstreet <kent.overstreet@...il.com>,
        security@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        kernel-team@...com
Subject: Re: [PATCH 7/7] RCU, workqueue: Implement rcu_work

Hello,

On Thu, Mar 08, 2018 at 08:29:53AM +0800, Lai Jiangshan wrote:
> I mentioned a subtle use case that user would think it is supported
> since the comment doesn't disallow it.
> 
> It is clear that the user expects
>    the work must be called at least once after the API returns
>    the work must be called after an RCU grace period
> 
> But in the case when the user expects the work must be called
> at least once again after "queue_rcu_work() + an RCU grace period",
> the API is not competent to it if the work is queued.
> Although the user can detect it by the return value of
> queue_rcu_work(), the user hardly makes his expectation
> happen by adding appropriate code.

We should definitely document it better but it isn't any different
from delayed_work, and I don't see a reason to deviate.

Thanks.

-- 
tejun