linux-kernel - Re: smp_call_function

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Date:	Fri, 3 Apr 2015 07:45:13 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Chris J Arges <chris.j.arges@...onical.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rafael David Tinoco <inaddy@...ntu.com>,
	Peter Anvin <hpa@...or.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Gema Gomez <gema.gomez-solano@...onical.com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: smp_call_function_single lockups


* Chris J Arges <chris.j.arges@...onical.com> wrote:

> 
> 
> On 04/02/2015 02:07 PM, Ingo Molnar wrote:
> > 
> > * Chris J Arges <chris.j.arges@...onical.com> wrote:
> > 
> >> Whenever we look through the crashdump we see csd_lock_wait waiting 
> >> for CSD_FLAG_LOCK bit to be cleared.  Usually the signature leading 
> >> up to that looks like the following (in the openstack tempest on 
> >> openstack and nested VM stress case)
> >>
> >> (qemu-system-x86 task)
> >> kvm_sched_in
> >>  -> kvm_arch_vcpu_load
> >>   -> vmx_vcpu_load
> >>    -> loaded_vmcs_clear
> >>     -> smp_call_function_single
> >>
> >> (ksmd task)
> >> pmdp_clear_flush
> >>  -> flush_tlb_mm_range
> >>   -> native_flush_tlb_others
> >>     -> smp_call_function_many
> > 
> > So is this two separate smp_call_function instances, crossing each 
> > other, and none makes any progress, indefinitely - as if the two IPIs 
> > got lost?
> > 
> 
> This is two different crash signatures. Sorry for the confusion.

So just in case, both crash signatures ought to be detected by the 
patch I just sent.

Thanks,

	Ingo
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