linux-kernel - Re: [PATCH 3/4] mm, oom: do not rely on TIF_MEMDIE for exit_oom

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Message-ID: <20161005093702.GB7138@dhcp22.suse.cz>
Date:   Wed, 5 Oct 2016 11:37:02 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 3/4] mm, oom: do not rely on TIF_MEMDIE for
 exit_oom_victim

On Tue 04-10-16 18:21:14, Oleg Nesterov wrote:
[...]
> so this can't detect the multi-threaded group exit, and ...
> 
> >  	list_for_each_entry_safe(p, n, &dead, ptrace_entry) {
> >  		list_del_init(&p->ptrace_entry);
> > -		release_task(p);
> > +		if (release_task(p) && p == tsk)
> > +			last = true;
> 
> this can only happen if this process auto-reaps itself. Not to mention
> that exit_notify() will never return true if traced.
> 
> No, this doesn't look right.

You are right. I should have noticed that. Especially when I was hunting
the strace hang bug. I started to have a bad feeling about this patch
but for some reason I just didn't put all the pieces together.

So the patch is completely b0rked. Back to drawing board and start
again. Oh well...

Anyway thanks and sorry to waste your time.

-- 
Michal Hocko
SUSE Labs