strace lockup when tracing exec in go

[Michal Hocko]

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