linux-kernel - Re: [PATCH v3] do_wait: make PIDTYPE

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Message-ID: <20210311151542.GB15552@redhat.com>
Date:   Thu, 11 Mar 2021 16:15:43 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Jim Newsome <jnewsome@...project.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian@...uner.io>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] do_wait: make PIDTYPE_PID case O(1) instead of O(n)

On 03/10, Jim Newsome wrote:
>
> On 3/10/21 16:40, Eric W. Biederman wrote:
>
> >> +static int do_wait_pid(struct wait_opts *wo)
> >> +{
> >> +	struct task_struct *target = pid_task(wo->wo_pid, PIDTYPE_PID);
> >                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > This is subtle change in behavior.
> >
> > Today on the task->children list we only place thread group leaders.
>
> Shouldn't we allow waiting on clone children if __WALL or __WCLONE is set?

Don't confuse clone child with child's sub-thread.

Oleg.