linux-kernel - Re: x86: disable preemption in delay

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: <20071116061332.GF16273@elte.hu>
Date:	Fri, 16 Nov 2007 07:13:32 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: x86: disable preemption in delay_tsc()


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> > >     x86: disable preemption in delay_tsc()
> > >     
> > >     Marin Mitov points out that delay_tsc() can misbehave if it is 
> > > preempted and rescheduled on a different CPU which has a skewed 
> > > TSC. Fix it by disabling preemption.
> > >  
> > 
> > this worries me.. this appears to effectively disable preemption 
> > during udelay() and mdelay() loops... which are very obvious latency 
> > inducers.
> > 
> > Now you can argue that if you're preemptible you should have used 
> > msleep() and co, and I'll totally buy that.
> > 
> > 
> > Maybe we should just check if we're still on the same cpu or 
> > something, or have a cheap way to pin a process to a cpu.... but 
> > both are longer term solutions.
> 
> Yes, we can do better.
> 
> But this bug can cause very rare failures in probably a large number 
> of device drivers on a minorty of machines.  Ugly.  So I felt it best 
> to plug it fast while people think about more sophisticated fixes.

how about using usleep() transparently if high-res timers are active and 
we have !preempt_count()? That would be a sufficient solution and would 
avoid all the calibration and per-cpu-ness problems.

	Ingo
-
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/