From: Michal Hocko <mhocko@kernel.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
strace-devel@lists.sourceforge.net,
Mike Galbraith <umgwanakikbuti@gmail.com>,
Aleksa Sarai <asarai@suse.com>
Subject: Re: strace lockup when tracing exec in go
Date: Fri, 23 Sep 2016 16:19:16 +0200 [thread overview]
Message-ID: <20160923141916.GR4478@dhcp22.suse.cz> (raw)
In-Reply-To: <20160923140724.GA29476@redhat.com>
On Fri 23-09-16 16:07:24, Oleg Nesterov wrote:
> 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 ;)
OK, now it makes more sense. I was really scratching my head to
understand this part...
> > > 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(),
Yes making de_thread completely independent on the state of the tracer
would be a huge improvement. While playing with this test case I
triggered some other interesting hangs (e.g. strace hanging in tty while
trying to print something). So just few interruptible waits is not a
full solution.
> but ooh I don't
> like this. Plus in this case we will need to finally define what
> PTRACE_EVENT_EXIT should actually do.
OK, considering this has been broken for quite some time I do not think
we are in hurry. I am slightly worried about how such a solution would
be stable kernel safe but ohh well.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2016-09-23 14:19 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-21 15:29 strace lockup when tracing exec in go Michal Hocko
2016-09-22 4:15 ` Mike Galbraith
2016-09-22 8:01 ` Michal Hocko
2016-09-22 8:20 ` Aleksa Sarai
2016-09-22 8:36 ` Michal Hocko
2016-09-22 9:40 ` Mike Galbraith
2016-09-22 9:53 ` Michal Hocko
2016-09-22 10:09 ` Mike Galbraith
2016-09-22 11:09 ` Michal Hocko
2016-09-22 13:53 ` Michal Hocko
2016-09-23 1:17 ` Aleksa Sarai
2016-09-23 10:21 ` Oleg Nesterov
2016-09-23 11:18 ` Michal Hocko
2016-09-23 13:21 ` Oleg Nesterov
2016-09-23 13:40 ` Michal Hocko
2016-09-23 14:07 ` Oleg Nesterov
2016-09-23 14:19 ` Michal Hocko [this message]
2016-09-23 9:50 ` Oleg Nesterov
2016-09-23 11:23 ` Michal Hocko
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