linux-kernel - Re: [RFC] tracing: Add support for critical section event tracing

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

Message-ID: <20170630170740.7a0eeaf5@gandalf.local.home>
Date:   Fri, 30 Jun 2017 17:07:40 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] tracing: Add support for critical section event tracing

On Fri, 30 Jun 2017 14:03:14 -0700
Joel Fernandes <joelaf@...gle.com> wrote:

> Hi Steven,
> 
> Thanks a lot for the comments, I agree with all of them and had a
> comment about one of them:
> 
> On Fri, Jun 30, 2017 at 5:51 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> [..]
> > Are you not worried about recursion here? There's no protection.
> > Wouldn't it be better to have:
> >
> >         if (!this_cpu_read(tracing_events_cpu))
> >                 return;
> >
> >         trace_critical_end(ip, parent_ip);
> >
> >         this_cpu_write(tracing_events_cpu, 0);
> >
> > ?
> >  
> 
> I tried to go over some scenarios and I think it shouldn't be a
> problem because we start the critical event only when either
> interrupts are turned off while preemption is turned on, or preempt is
> turned off while interrupts are turned on, and the fact that we call
> the tracer while still in the critical section. Let me know if you had
> a scenario in mind that can cause problems with this.

Then may I ask what is tracing_events_cpu actually protecting?

-- Steve