linux-kernel - Re: [Xen-devel] Re: [PATCH 08/23] xen: statically initialize cpu_evtchn_mask

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Date:	Tue, 25 Jan 2011 14:02:17 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jan Beulich <JBeulich@...ell.com>,
	"Konrad Rzeszutek Wilk" <konrad@...nel.org>,
	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>
Subject: Re: [Xen-devel] Re: [PATCH 08/23] xen: statically initialize
 cpu_evtchn_mask_p

On Mon, 2011-01-24 at 17:44 +0000, Paolo Bonzini wrote:
> On 10/12/2010 05:44 PM, Konrad Rzeszutek Wilk wrote:
> > -static struct cpu_evtchn_s *cpu_evtchn_mask_p;
> > +
> > +static __initdata struct cpu_evtchn_s init_evtchn_mask = {
> > +	.bits[0 ... (NR_EVENT_CHANNELS/BITS_PER_LONG)-1] = ~0ul,
> > +};
> > +static struct cpu_evtchn_s *cpu_evtchn_mask_p =&init_evtchn_mask;
> > +
> >   static inline unsigned long *cpu_evtchn_mask(int cpu)
> >   {
> >   	return cpu_evtchn_mask_p[cpu].bits;
> 
> This causes a modpost warning:
> 
>     WARNING: drivers/xen/built-in.o(.data+0x0): Section mismatch in
>     reference from the variable cpu_evtchn_mask_p to the variable
>     .init.data:init_evtchn_mask
> 
>     The variable cpu_evtchn_mask_p references
>     the variable __initdata init_evtchn_mask
> 
>     If the reference is valid then annotate the
>     variable with __init* or __refdata (see linux/init.h) or name the variable:
>     *driver, *_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console, 
> 
> This is harmless, the variable is initialized to non-init data
> in an __init function.  The added noise is ugly, though.

Does this help? If I understand the comment which precedes  __initref
correctly it is intended to address precisely this situation.

Ian.
8<---------

xen: events: mark cpu_evtchn_mask_p as __refdata

This variable starts out pointing at init_evtchn_mask which is marked
__initdata but is set to point to a non-init data region in xen_init_IRQ
which is itself an __init function so this is safe.

Signed-off-by: Ian Campbell <ian.campbell@...rix.com>

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 31af0ac..5061af0 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -114,7 +114,7 @@ struct cpu_evtchn_s {
 static __initdata struct cpu_evtchn_s init_evtchn_mask = {
 	.bits[0 ... (NR_EVENT_CHANNELS/BITS_PER_LONG)-1] = ~0ul,
 };
-static struct cpu_evtchn_s *cpu_evtchn_mask_p = &init_evtchn_mask;
+static struct __refdata cpu_evtchn_s *cpu_evtchn_mask_p =
&init_evtchn_mask;
 
 static inline unsigned long *cpu_evtchn_mask(int cpu)
 {



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