linux-kernel - Re: [PATCH 4/5] pidfd: add CLONE_WAIT

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Message-ID: <20190725103048.GE4707@redhat.com>
Date:   Thu, 25 Jul 2019 12:30:48 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     Christian Brauner <christian@...uner.io>,
        kernel list <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tejun Heo <tj@...nel.org>, David Howells <dhowells@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        kernel-team <kernel-team@...roid.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH 4/5] pidfd: add CLONE_WAIT_PID

On 07/24, Jann Horn wrote:
>
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1902,6 +1902,10 @@ static __latent_entropy struct task_struct *copy_process(
>         delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
>         p->flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER | PF_IDLE);
>         p->flags |= PF_FORKNOEXEC;
> +       if (!(clone_flags & CLONE_THREAD))
> +               p->flags &= ~PF_PF_WAIT_PID;
> +       if (clone_flags & CLONE_WAIT_PID)
> +               p->flags |= PF_PF_WAIT_PID;

agreed, but then the "if (!thread_group_leader(tsk))" block in de_thread()
should also copy PF_PF_WAIT_PID.

> An alternative would be to not use p->flags at all, but instead make
> this a property of the signal_struct - since the property is shared by
> all threads, that might make more sense?

I tend to agree.

Oleg.