Date: Fri, 3 Apr 2015 07:45:13 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Chris J Arges <chris.j.arges@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Rafael David Tinoco <inaddy@ubuntu.com>, Peter Anvin <hpa@zytor.com>,
        Jiang Liu <jiang.liu@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>, Jens Axboe <axboe@kernel.dk>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Gema Gomez <gema.gomez-solano@canonical.com>,
        the arch/x86 maintainers <x86@kernel.org>
Subject: Re: smp_call_function_single lockups
Message-ID: <20150403054512.GA11041@gmail.com>
References: <20150331222327.GA12512@canonical.com>
 <20150401124336.GB12841@gmail.com>
 <20150401161047.GD12730@canonical.com>
 <CA+55aFxQ6q7MNS+4XWZ3=Xa0Hz6kumd84v_aEw3M4gBpXszTkQ@mail.gmail.com>
 <551C6A48.9060805@canonical.com>
 <CA+55aFw2Jb4ASOxckY1cwP23fAYv5dG1WYCkB6RyjjpP2hEQcw@mail.gmail.com>
 <20150402182607.GA8896@gmail.com>
 <551D8FAF.5070805@canonical.com>
 <20150402190725.GA10570@gmail.com>
 <551DB0E2.1020607@canonical.com>
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* Chris J Arges <chris.j.arges@canonical.com> wrote:

> 
> 
> On 04/02/2015 02:07 PM, Ingo Molnar wrote:
> > 
> > * Chris J Arges <chris.j.arges@canonical.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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