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Date:   Thu, 25 Jul 2019 12:30:48 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Jann Horn <jannh@google.com>
Cc:     Christian Brauner <christian@brauner.io>,
        kernel list <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
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        Ingo Molnar <mingo@redhat.com>,
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Subject: Re: [PATCH 4/5] pidfd: add CLONE_WAIT_PID
Message-ID: <20190725103048.GE4707@redhat.com>
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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.