linux-kernel - Re: [PATCH v2 2/2] prctl: propagate has_child

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Message-ID: <20170130125141.GA22583@redhat.com>
Date:   Mon, 30 Jan 2017 13:51:42 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Michal Hocko <mhocko@...e.com>,
        Stanislav Kinsburskiy <skinsbursky@...tuozzo.com>,
        Mateusz Guzik <mguzik@...hat.com>,
        linux-kernel@...r.kernel.org,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Konstantin Khorenko <khorenko@...tuozzo.com>,
        Lennart Poettering <lennart@...ttering.net>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Kay Sievers <kay.sievers@...y.org>
Subject: Re: [PATCH v2 2/2] prctl: propagate has_child_subreaper flag to
 every descendant

On 01/27, Pavel Tikhomirov wrote:
>
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1725,6 +1725,8 @@ struct task_struct {
>  	struct signal_struct *signal;
>  	struct sighand_struct *sighand;
>  
> +	struct list_head csr_descendant;
> +

You forgot to remove this part ;)

> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1367,9 +1367,6 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
>  	sig->oom_score_adj = current->signal->oom_score_adj;
>  	sig->oom_score_adj_min = current->signal->oom_score_adj_min;
>  
> -	sig->has_child_subreaper = current->signal->has_child_subreaper ||
> -				   current->signal->is_child_subreaper;
> -
>  	mutex_init(&sig->cred_guard_mutex);
>  
>  	return 0;
> @@ -1800,6 +1797,13 @@ static __latent_entropy struct task_struct *copy_process(
>  
>  			p->signal->leader_pid = pid;
>  			p->signal->tty = tty_kref_get(current->signal->tty);
> +			/*
> +			 * Inherit has_child_subreaper flag under the same
> +			 * tasklist_lock with adding child to the process tree
> +			 * for propagate_has_child_subreaper optimization.
> +			 */
> +			p->signal->has_child_subreaper = current->signal->has_child_subreaper ||
> +							 current->signal->is_child_subreaper;

Ah yes, we need this change too...

And perhaps it would be more correct to do

			p->signal->has_child_subreaper =
				p->real_parent->signal->has_child_subreaper ||
				p->real_parent->signal->is_child_subreaper;

the current code is not exactly right if CLONE_PARENT...

Oleg.