linux-kernel - Re: [BUG] kvm crashes in 2.6.28-rc6-00007-ged31348

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Date:	Tue, 2 Dec 2008 20:46:11 +0000
From:	Luis Henriques <henrix@...o.pt>
To:	Steven Rostedt <srostedt@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [BUG] kvm crashes in 2.6.28-rc6-00007-ged31348

On Tue, Dec 02, 2008 at 03:25:09PM -0500, Steven Rostedt wrote:
> [ added Ingo too ]
> 
> On Tue, 2008-12-02 at 19:46 +0000, Luis Henriques wrote:
> > (I am CC'ing to Steven Rostedt since he might be interested on this)
> > 
> > On Tue, Dec 02, 2008 at 07:09:14PM +0000, Luis Henriques wrote:
> 
> > I have some other information to had to my previous email.  However, I do not
> > know whether it is related with my first bug report.
> > 
> > It looks like ftrace may stop the CPUs in some situations and I have been
> > playing with ftrace for some time.  So, here's what I just did:  started ftrace
> > with function tracer and then started kvm.  I got ugly crashes and apparently
> > quite easy to reproduce (I get complete freeze or immediate reboot).
> > 
> > I did not investigated this issue and, again, it may not be related with my
> > initial report but there's definitely something wrong here, right?
> > 
> > (just to refresh, I am using 2.6.28-rc6-00007-ged31348 in x86_64 machine)
> > 
> 
> Hi,
> 
> ftrace only stops the CPUs on start up or shutdown of the function
> tracer (i.e. echo function > /debugfs/tracing/current_tracer).  It does
> not stop the CPUs at any other time.

Ok, I suspected that it was like this but was not sure.

> Now what ftrace does do, is to call a tracing function at pretty much
> every function call in the kernel. In most places this is fine, but
> there are some cases that this can be an issue. For example, we can not
> trace suspend and resume because on resume smp_processor_id() is
> undefined, which ftrace uses.
> 
> The following must be available without recursion for the function
> tracer to work:
> 
>   local_irq_save/restore
>   smp_processor_id
>   preempt_enable/disable_notrace
>   atomic_inc/dec
> 
> There could be other things that might be causing the crash. Do you have
> a crash dump and config available?

Unfortunately, I have only my laptop (where the crash is occuring) and no
serial port on it (I am not able to get any output from the console).  Do you
have any suggestion on how to collect information on the crash?  I can try to
configure Kdump to capture more info.

Anyway, my .config is attached...

-- 
Luis Henriques


View attachment ".config" of type "text/plain" (69354 bytes)