linux-kernel - Re: bisected: 'perf top' causing soft lockups under Xen

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 for Android: free password hash cracker in your pocket

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

Date:	Wed, 15 Feb 2012 01:32:04 -0800
From:	Steven Noonan <steven@...inklabs.net>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ben Guthro <ben@...hro.net>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: bisected: 'perf top' causing soft lockups under Xen

On Wed, Feb 15, 2012 at 10:25:44AM +0100, Peter Zijlstra wrote:
> On Wed, 2012-02-15 at 00:57 -0800, Steven Noonan wrote:
> > It seems to me that there are two options for fixing this, but I'm
> > probably lacking the necessary context (or experience with Xen). Either:
> > 
> > - The patch provided by Ben needs to have additional work to specially
> >   handle IRQ_WORK_VECTOR, since it seems to be a special case where
> >   there's no event channel attached for it. Perhaps adding an event
> >   channel for this is the fix? Seems high-overhead, but I lack a good
> >   understanding of how interrupts are handled in Xen.
> 
> So that's a self-IPI, is Xen failing to implement this?

Yes.

Ben's patch implements it, but it explodes (NULL pointer dereference)
when it can't find an event channel for IRQ_WORK_VECTOR.

> 
> > or
> > 
> > - Perf needs to be "enlightened" about Xen and avoid sending an IPI in
> >   the first place.
> 
> Uhm, no. If anything Xen should simply not implement
> arch_irq_work_raise(). The callbacks are then ran from the timer
> interrupt.

Sorry, wild guess. I'm a kernel newbie. :)
--
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/