linux-kernel - Re: [PATCH 1/5] seccomp: don't use semaphore and wait

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Date:   Thu, 20 Oct 2022 21:30:03 -0700
From:   Andrei Vagin <avagin@...il.com>
To:     Kees Cook <kees@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Christian Brauner <brauner@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Oskolkov <posk@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tycho Andersen <tycho@...ho.pizza>,
        Will Drewry <wad@...omium.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH 1/5] seccomp: don't use semaphore and wait_queue together

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@...il.com> wrote:
> >Here is no reason to use two different primitives that do similar things.
> >
> >Signed-off-by: Andrei Vagin <avagin@...il.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