linux-kernel - Re: WARNING: at arch/x86/kernel/smp.c:119 native_smp_send

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:	Fri, 10 Feb 2012 20:03:53 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Sasha Levin <levinsasha928@...il.com>,
	Josh Boyer <jwboyer@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Avi Kivity <avi@...hat.com>, kvm <kvm@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	x86 <x86@...nel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Don Zickus <dzickus@...hat.com>
Subject: Re: WARNING: at arch/x86/kernel/smp.c:119
 native_smp_send_reschedule+0x25/0x43()

On Fri, 2012-02-10 at 19:58 +0100, Peter Zijlstra wrote:
> OK, so a 'modern' kernel does it slightly different and I've no idea
> what exactly goes wrong in your vintage version. But I can see the
> current stuff going at it all wrong.
> 
> What seems to happen is that native_nmi_stop_other_cpus() NMI broadcasts
> for smp_stop_nmi_callback()->stop_this_cpu(). Which without any
> serialization what so ever marks all remote CPUs offline and calls halt
> with IRQs disabled -> dead.
> 
> While we're waiting for this all to complete, the scheduler tries to
> no_hz load-balance and kick a cpu it thinks is still around and we get
> the above splat because the NMI just marked it offline without telling
> anybody about it.
> 
> Now, arguably you don't want to go through the whole hotplug crap to
> shut down your machine, esp not on panic, but clearing the online state
> without telling anybody about it is bound to lead to these things.
> 
> No immediate solution comes to mind... 

Don, any reason you wait for the NMI broadcast to complete with IRQs
enabled? If you disable IRQs before the broadcast the interrupt can't
happen and should side-step this particular problem.

Its not like we have 'latency' issues on this path :-)

--
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/