Subject: Re: [RFC PATCH] Fix Oops in rtas_stop_self()

From: Li Zhong <[email-masked]>
Date: Mon, 28 Apr 2014 08:26:45 +0800

On Fri, 2014-04-25 at 22:18 +1000, Anton Blanchard wrote:
> Hi,
> 
> > When trying offline cpus, I noticed following Oops in
> > rtas_stop_self(), and it seems caused by commit 41dd03a9. The Oops
> > disappears after reverting this commit.
> > 
> > After reading the code, I guess it might be caused by moving the
> > rtas_args to stack. Still need some more time to read enter_rtas to
> > understand why it happens, but the problem seems could be solved by
> > moving the rtas_args away from stack by adding static before it.
> 
> Nice catch. RTAS is 32bit and if your box has more than 4GB RAM then
> your stack could easily be outside 32bit range.

Ah, yes, the stack here is obviously at a much higher address than 4GB.

> 
> You can add:
> 
> Signed-off-by: Anton Blanchard <[email-masked]>
> 
> And also:
> 
> Cc: [email-masked] # 3.14+

OK, 

Thanks, Zhong
> 
> > Signed-off-by: Li Zhong <[email-masked]>
> > ---
> >  arch/powerpc/platforms/pseries/hotplug-cpu.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c
> > b/arch/powerpc/platforms/pseries/hotplug-cpu.c index 9b8e050..20d6297
> > 100644 --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
> > +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
> > @@ -88,13 +88,14 @@ void set_default_offline_state(int cpu)
> >  
> >  static void rtas_stop_self(void)
> >  {
> > -	struct rtas_args args = {
> > -		.token = cpu_to_be32(rtas_stop_self_token),
> > +	static struct rtas_args args = {
> >  		.nargs = 0,
> >  		.nret = 1,
> >  		.rets = &args.args[0],
> >  	};
> >  
> > +	args.token = cpu_to_be32(rtas_stop_self_token);
> > +
> >  	local_irq_disable();
> >  
> >  	BUG_ON(rtas_stop_self_token == RTAS_UNKNOWN_SERVICE);
> > 
> > 
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>