Re: [PATCH 7/7] RCU, workqueue: Implement rcu_work

From: Tejun Heo <tj@kernel.org>
To: Lai Jiangshan <jiangshanlai+lkml@gmail.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	torvalds@linux-foundation.org, Jann Horn <jannh@google.com>,
	bcrl@kvack.org, viro@zeniv.linux.org.uk,
	Kent Overstreet <kent.overstreet@gmail.com>,
	security@kernel.org, LKML <linux-kernel@vger.kernel.org>,
	kernel-team@fb.com
Subject: Re: [PATCH 7/7] RCU, workqueue: Implement rcu_work
Date: Fri, 9 Mar 2018 08:21:37 -0800	[thread overview]
Message-ID: <20180309162137.GC2943022@devbig577.frc2.facebook.com> (raw)
In-Reply-To: <CAJhGHyDEpXG88uDHiogxUH0Yp5sU3v1p-kUSvJbGYCZ+HGucvQ@mail.gmail.com>

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