Re: [PATCH 4/5] pidfd: add CLONE_WAIT_PID

From: Christian Brauner <christian@brauner.io>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Jann Horn <jannh@google.com>,
	kernel list <linux-kernel@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Kees Cook <keescook@chromium.org>,
	"Joel Fernandes (Google)" <joel@joelfernandes.org>,
	Thomas Gleixner <tglx@linutronix.de>, Tejun Heo <tj@kernel.org>,
	David Howells <dhowells@redhat.com>,
	Andy Lutomirski <luto@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Aleksa Sarai <cyphar@cyphar.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	kernel-team <kernel-team@android.com>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH 4/5] pidfd: add CLONE_WAIT_PID
Date: Thu, 25 Jul 2019 12:36:02 +0200	[thread overview]
Message-ID: <20190725103601.4ck4bpsdsgcpdknt@brauner.io> (raw)
In-Reply-To: <20190725103048.GE4707@redhat.com>

On Thu, Jul 25, 2019 at 12:30:48PM +0200, Oleg Nesterov wrote:
> 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.

Hm, ok. That's two people that prefer to make this a flag in
signal_struct. Ok, let me adapt the patch.

Thanks!
Christian