linux-kernel - Re: [PATCH v2] exec: don't force_sigsegv processes with a pending fatal signal

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Message-ID: <20190211232042.GA18232@visor>
Date:   Mon, 11 Feb 2019 15:20:42 -0800
From:   Ivan Delalande <colona@...sta.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v2] exec: don't force_sigsegv processes with a pending
 fatal signal

On Mon, Feb 11, 2019 at 06:12:53PM +0100, Oleg Nesterov wrote:
> sorry, I couldn't look at this patch before.
> 
> On 02/04, Ivan Delalande wrote:
> >
> > --- a/fs/exec.c
> > +++ b/fs/exec.c
> > @@ -1660,7 +1660,12 @@ int search_binary_handler(struct linux_binprm *bprm)
> >  		if (retval < 0 && !bprm->mm) {
> >  			/* we got to flush_old_exec() and failed after it */
> >  			read_unlock(&binfmt_lock);
> > -			force_sigsegv(SIGSEGV, current);
> > +			if (!fatal_signal_pending(current)) {
> > +				if (print_fatal_signals)
> > +					pr_info("load_binary() failed: %d\n",
> > +						retval);
> 
> I won't argue, but do we really want this spam?
> 
> > +				force_sigsegv(SIGSEGV, current);
> > +			}
> >  			return retval;
> >  		}
> >  		if (retval != -ENOEXEC || !bprm->file) {
> > diff --git a/kernel/signal.c b/kernel/signal.c
> > index e1d7ad8e6ab1..674076e63624 100644
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -2552,10 +2552,10 @@ static void signal_delivered(struct ksignal *ksig, int stepping)
> >
> >  void signal_setup_done(int failed, struct ksignal *ksig, int stepping)
> >  {
> > -	if (failed)
> > -		force_sigsegv(ksig->sig, current);
> > -	else
> > +	if (!failed)
> >  		signal_delivered(ksig, stepping);
> > +	else if (!fatal_signal_pending(current))
> > +		force_sigsegv(ksig->sig, current);
> 
> The changelog doesn't explain this change.
> 
> OK, I guess it comes from the previous discussion, setup_rt_frame() can equally fail
> if fatal_signal_pending(). But this should be documented at least in the changelog,
> and I still think we could simply change force_sigsegv() instead.
> 
> In any case, Eric has already mentioned that we going to give SIGKILL more priority,
> so I think we can drop this patch?

Yes, I've been running our tests on top of Eric's tree over the week-end
and haven't seen any new hit. I also see that Andrew has dropped the
patch from -mm, so no futher action should be required here.

Thank you for taking a look at the patch anyway.

-- 
Ivan Delalande
Arista Networks