linux-kernel - Re: [RFC 2/3] preempt_tracer: Disable IRQ while starting/stopping due to a preempt

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: <20190529132926.GV2650@hirez.programming.kicks-ass.net>
Date:   Wed, 29 May 2019 15:29:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org, williams@...hat.com,
        daniel@...stot.me, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Yangtao Li <tiny.windzz@...il.com>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>
Subject: Re: [RFC 2/3] preempt_tracer: Disable IRQ while starting/stopping
 due to a preempt_counter change

On Wed, May 29, 2019 at 03:19:57PM +0200, Peter Zijlstra wrote:
> On Wed, May 29, 2019 at 08:39:30AM -0400, Steven Rostedt wrote:
> > I believe I see what Daniel is talking about, but I hate the proposed
> > solution ;-)
> > 
> > First, if you care about real times that the CPU can't preempt
> > (preempt_count != 0 or interrupts disabled), then you want the
> > preempt_irqsoff tracer. The preempt_tracer is more academic where it
> > just shows you when we disable preemption via the counter. But even
> > with the preempt_irqsoff tracer you may not get the full length of time
> > due to the above explained race.
> 
> IOW, that tracer gives a completely 'make believe' number? What's the
> point? Just delete the pure preempt tracer.

Alternatively, fix the preempt tracer by having it completely disregard
IRQs.