linux-kernel - Re: strace lockup when tracing exec in go

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Message-ID: <20160923111808.GJ4478@dhcp22.suse.cz>
Date:   Fri, 23 Sep 2016 13:18:09 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        strace-devel@...ts.sourceforge.net,
        Mike Galbraith <umgwanakikbuti@...il.com>,
        Aleksa Sarai <asarai@...e.com>
Subject: Re: strace lockup when tracing exec in go

On Fri 23-09-16 12:21:41, Oleg Nesterov wrote:
> On 09/22, Michal Hocko wrote:
> >
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -91,6 +91,10 @@ static int sig_ignored(struct task_struct *t, int sig, bool force)
> >  	if (!sig_task_ignored(t, sig, force))
> >  		return 0;
> >  
> > +	/* Do not ignore signals sent from child to the parent */
> > +	if (current->ptrace && current->parent == t)
> > +		return 0;
> 
> This doesn't look right in general, and this can't really help.
> 
> This assumes that the tracer will call do_wait() after mm_access()
> fails, but this is not necessarily true.
> 
> Note also ptrace_attach(), -ERESTARTNOINTR means that the tracer won't
> even return to user-space if SIGCHLD is ignored, the tracer will silently
> restart the syscall.

Well, it apparently does help the strace case. So I am not arguing this
is the best fix but can it be harmful?
-- 
Michal Hocko
SUSE Labs