From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760079AbcIWOIY (ORCPT ); Fri, 23 Sep 2016 10:08:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51564 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758881AbcIWOIX (ORCPT ); Fri, 23 Sep 2016 10:08:23 -0400 Date: Fri, 23 Sep 2016 16:07:24 +0200 From: Oleg Nesterov To: Michal Hocko Cc: LKML , strace-devel@lists.sourceforge.net, Mike Galbraith , Aleksa Sarai Subject: Re: strace lockup when tracing exec in go Message-ID: <20160923140724.GA29476@redhat.com> References: <20160922083602.GB11875@dhcp22.suse.cz> <1474537209.5022.8.camel@gmail.com> <20160922095303.GD11875@dhcp22.suse.cz> <1474538945.5022.20.camel@gmail.com> <20160922110925.GE11875@dhcp22.suse.cz> <20160922135301.GF11875@dhcp22.suse.cz> <20160923102141.GA16189@redhat.com> <20160923111808.GJ4478@dhcp22.suse.cz> <20160923132101.GA27178@redhat.com> <20160923134058.GP4478@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160923134058.GP4478@dhcp22.suse.cz> User-Agent: Mutt/1.5.18 (2008-05-17) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 23 Sep 2016 14:08:22 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/23, Michal Hocko wrote: > > On Fri 23-09-16 15:21:02, Oleg Nesterov wrote: > > > > This change is simply wrong no matter what. > > I've just tried to extend the existing > > /* > * Tracers may want to know about even ignored signals. > */ > return !t->ptrace; > > but I probably just do not understand what that actually means. I > thought that the tracer is _really_ interested in hearing about the > signal. Yes, the tracer is really interested to know that a signal was sent to the _tracee_, not the tracer ;) > > > We could change do_notify_parent() > > to call signal_wake_up() if tsk->ptrace, but see above, this won't help. > > So does this mean WONTFIX? Can we at least document this behavior? It > surely is unexpected. No, no, no. Of course this must be fixed. The only problem is that I still do not know what should we do. I'll try to return to this problem next week. I'm afraid we will need to change de_thread() to wait until all other sub- threads have passed exit_notify() or even exit_signals(), but ooh I don't like this. Plus in this case we will need to finally define what PTRACE_EVENT_EXIT should actually do. Oleg.