linux-kernel - Re: [PATCH v1 1/1] waitid: Add support for waiting for the current process group

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Message-ID: <20190814122909.GA11595@redhat.com>
Date:   Wed, 14 Aug 2019 14:29:10 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     christian.brauner@...ntu.com
Cc:     linux-kernel@...r.kernel.org, libc-alpha@...rceware.org,
        alistair23@...il.com, ebiederm@...ssion.com, arnd@...db.de,
        dalias@...c.org, torvalds@...ux-foundation.org,
        adhemerval.zanella@...aro.org, fweimer@...hat.com,
        palmer@...ive.com, macro@....com, zongbox@...il.com,
        akpm@...ux-foundation.org, viro@...iv.linux.org.uk, hpa@...or.com
Subject: Re: [PATCH v1 1/1] waitid: Add support for waiting for the current
 process group

On 08/14, christian.brauner@...ntu.com wrote:
>
>  	case P_PGID:
>  		type = PIDTYPE_PGID;
> -		if (upid <= 0)
> +		if (upid < 0)
>  			return -EINVAL;
> +
> +		if (upid == 0)
> +			pid = get_pid(task_pgrp(current));

this needs rcu lock or tasklist_lock, this can race with another thread
doing sys_setpgid/setsid (see change_pid(PIDTYPE_PGID)).

Oleg.