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Date:   Wed, 24 Jul 2019 18:53:39 +0200
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Subject: Re: [PATCH] pidfd: Add warning if exit_state is 0 during notification
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        linux-kernel@vger.kernel.org
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Oleg Nesterov <oleg@redhat.com>
From:   Christian Brauner <christian@brauner.io>
Message-ID: <3724AB8D-81A8-40B7-A025-95CD6BAAA6D8@brauner.io>
Sender: linux-kernel-owner@vger.kernel.org
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On July 24, 2019 6:48:16 PM GMT+02:00, "Joel Fernandes (Google)" <joel@joel=
fernandes=2Eorg> wrote:
>Previously a condition got missed where the pidfd waiters are awakened
>before the exit_state gets set=2E This can result in a missed
>notification
>[1] and the polling thread waiting forever=2E
>
>It is fixed now, however it would be nice to avoid this kind of issue
>going unnoticed in the future=2E So just add a warning to catch it in the
>future=2E
>
>[1]
>https://lore=2Ekernel=2Eorg/lkml/20190717172100=2E261204-1-joel@joelferna=
ndes=2Eorg/
>
>Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes=2Eorg>
>---
> kernel/signal=2Ec | 1 +
> 1 file changed, 1 insertion(+)
>
>diff --git a/kernel/signal=2Ec b/kernel/signal=2Ec
>index 91b789dd6e72=2E=2E349f5a67f100 100644
>--- a/kernel/signal=2Ec
>+++ b/kernel/signal=2Ec
>@@ -1885,6 +1885,7 @@ static void do_notify_pidfd(struct task_struct
>*task)
> {
> 	struct pid *pid;
>=20
>+	WARN_ON(task->exit_state =3D=3D 0);
> 	pid =3D task_pid(task);
> 	wake_up_all(&pid->wait_pidfd);
> }

Makes sense to me=2E
I'm picking this up unless someone sees a problem with this patch=2E

Reviewed-by: Christian Brauner <christian@brauner=2Eio>