Re: [PATCH 1/5] seccomp: don't use semaphore and wait_queue together

From: Andrei Vagin <avagin@gmail.com>
To: Kees Cook <kees@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	Andy Lutomirski <luto@amacapital.net>,
	Christian Brauner <brauner@kernel.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Kees Cook <keescook@chromium.org>, Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Peter Oskolkov <posk@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Tycho Andersen <tycho@tycho.pizza>,
	Will Drewry <wad@chromium.org>,
	Vincent Guittot <vincent.guittot@linaro.org>
Subject: Re: [PATCH 1/5] seccomp: don't use semaphore and wait_queue together
Date: Thu, 20 Oct 2022 21:30:03 -0700	[thread overview]
Message-ID: <Y1IgS3w/M1vnEC8D@gmail.com> (raw)
In-Reply-To: <F4707F74-22D4-402B-8FC6-992AEADDFD33@kernel.org>

On Wed, Oct 19, 2022 at 10:10:44PM -0700, Kees Cook wrote:
> On October 19, 2022 6:10:44 PM PDT, Andrei Vagin <avagin@gmail.com> wrote:
> >Here is no reason to use two different primitives that do similar things.
> >
> >Signed-off-by: Andrei Vagin <avagin@gmail.com>
> >---
> > kernel/seccomp.c | 41 ++++++++++++++++++++++++++++++++++++-----
> > 1 file changed, 36 insertions(+), 5 deletions(-)
> 
> The commit log does not justify adding 29 lines to "do similar
> things". :) Can you describe the rationale and benefits here a bit
> more? I assume this to use the the future new wake_up helper?

The main reason is to use new wake_up helpers, but there are a few
other reasons:

* if we use two different ways, we always need to call them both. This
  patch fixes seccomp_notify_recv where we forgot to call wake_up_poll
  in the error path.

* If we use one primitive, we can control how many waiters are woken up
  for each request. Our goal is to wake up just one that will handle a
  request. Right now, wake_up_poll may wake up one waiter and
  up(&match->notif->request) may wake up one more.

I will update the commit message. Thanks!

> 
> 
> -- 
> Kees Cook