linux-kernel - Re: [RFC][PATCH 0/2] preempt: Track unmatched preempt_enable() to 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]

Date:	Thu, 16 Jan 2014 19:42:51 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Clark Williams <williams@...hat.com>
Subject: Re: [RFC][PATCH 0/2] preempt: Track unmatched preempt_enable() to
 preempt_disable()

On Thu, Jan 16, 2014 at 01:39:06PM -0500, Steven Rostedt wrote:
> On Thu, 16 Jan 2014 18:45:36 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Thu, Jan 16, 2014 at 12:18:24PM -0500, Steven Rostedt wrote:
> > 
> > Didn't see anything horrible in there, so fine with me.
> > 
> > Another thing I recently ran into was:
> > 
> >   local_irq_disable();
> >   preempt_disable();
> >   local_irq_enable();
> > 
> >   local_irq_disable();
> >   preempt_enable();
> >   local_irq_enable();
> > 
> > I'm not sure any of our debugging catches that, I meant to extend
> > lockdep, but maybe it could also be hooked into something else.
> 
> Hmm, what's wrong with the above?

Suppose a reschedule interrupt happens in the middle; we set
NEED_RESCHED but won't act because preempt is disabled.

When we hit preempt_enable() we'll call into preempt_schedule() but fail
because preemptible() finds irqs_disabled().

And in the end we do not schedule, but have NEED_RESCHED set.

FAIL.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/