linux-kernel - Re: rcu-bh design

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Sat, 05 May 2018 00:39:36 +0000
From:   Joel Fernandes <joelaf@...gle.com>
To:     Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:     "Joel Fernandes (Google)" <joel.opensrc@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: rcu-bh design

On Fri, May 4, 2018 at 4:42 PM Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
wrote:
[..]
> > Say that the tracepoint code is buggy and for some reason a
> > call_srcu wasn't done. For example, say the hypothetical bug I'm
> > taking about is in tracepoint_remove_func which called the
> > rcu_assign_pointer, but didn't call release_probes:
> >
> > diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> > index d0639d917899..f54cb358f451 100644
> > --- a/kernel/tracepoint.c
> > +++ b/kernel/tracepoint.c
> > @@ -216,7 +216,6 @@ static int tracepoint_add_func(struct tracepoint
*tp,
> >         rcu_assign_pointer(tp->funcs, tp_funcs);
> >         if (!static_key_enabled(&tp->key))
> >                 static_key_slow_inc(&tp->key);
> > -       release_probes(old);
> >         return 0;
> >  }
> > ---
> > I want to catching this from the test code. If I did the following,
> > it would be insufficient then:
> >
> > trace_probe_register(...);
> > srcu_barrier(&my_srcu_struct);  // only tells me any queued calls
> >                               // are done but not that something
> >                               // was queued
> >
> > I was seeing if I could use my_srcu_struct::completed for that. but
> > I'm not sure if that'll work (or that its legal to access it
> > directly - but hey this is just test code! :P).

> This is a bit ugly to do programmatically in the kernel.  The callbacks
> are on per-CPU queues that cannot be safely accessed except by that CPU.
> Plus they are on singly linked lists that can be quite long, so it could
> be insanely slow as well.

> But given that this is test code, why not leverage event tracing?
> There are some relevant events in include/trace/events/rcu.h, starting
> with the rcu_callback trace event.


Sounds like a great idea. I'll try that, thanks.

- Joel