linux-kernel - Re: [PATCH]gx-suspmod.c use boot_cpu_data instead of current_cpu

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Message-Id: <20070725212638.79bc3945.akpm@linux-foundation.org>
Date:	Wed, 25 Jul 2007 21:26:38 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Dave Young" <hidave.darkstar@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	"Dave Jones" <davej@...emonkey.org.uk>, cpufreq@....linux.org.uk
Subject: Re: [PATCH]gx-suspmod.c use boot_cpu_data instead of
 current_cpu_data

On Thu, 26 Jul 2007 04:20:10 +0000 "Dave Young" <hidave.darkstar@...il.com> wrote:

> >On 7/25/07, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > On Wed, 25 Jul 2007 14:19:05 +0000 Dave Young <hidave.darkstar@...il.com> wrote:
> >
> > > Hi,
> > > in preemptible kernel will report BUG: using smp_processor_id() in preemptible, so use boot_cpu_data instead of current_cpu_data.
> > >
> > > Signed-off-by: Dave Young <hidave.darkstar@...il.com>
> > >
> > > ---
> > > arch/i386/kernel/cpu/cpufreq/gx-suspmod.c |    4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff -pur linux/arch/i386/kernel/cpu/cpufreq/gx-suspmod.c linux.new/arch/i386/kernel/cpu/cpufreq/gx-suspmod.c
> > > --- linux/arch/i386/kernel/cpu/cpufreq/gx-suspmod.c   2007-07-25 14:11:06.000000000 +0000
> > > +++ linux.new/arch/i386/kernel/cpu/cpufreq/gx-suspmod.c       2007-07-25 13:57:29.000000000 +0000
> > > @@ -181,8 +181,8 @@ static __init struct pci_dev *gx_detect_
> > >       struct pci_dev *gx_pci = NULL;
> > >
> > >       /* check if CPU is a MediaGX or a Geode. */
> > > -     if ((current_cpu_data.x86_vendor != X86_VENDOR_NSC) &&
> > > -         (current_cpu_data.x86_vendor != X86_VENDOR_CYRIX)) {
> > > +     if ((boot_cpu_data.x86_vendor != X86_VENDOR_NSC) &&
> > > +         (boot_cpu_data.x86_vendor != X86_VENDOR_CYRIX)) {
> > >               dprintk("error: no MediaGX/Geode processor found!\n");
> > >               return NULL;
> > >       }
> >
> > um, I suspect it really wants to get at the current CPU.  But putting a
> > preempt_disable() around just that code is meaningless: the current CPU
> > could change immediately before or after the code block. It needs deeper
> > fixing, methinks.
> The only target is to get the cpu vendor, so boot_cpu_data is enough,
> the drivers/mtd/nand/cs553x_nand.c has the same usage.

I think there's some vague ambition in there to support non-identical CPUs.
In which case reading from the local CPU would make more sense.  (waves
frantically at cpufreq developers).

otoh, it'll take some work I suspect.  It'll need to sort out the overall
scope of "local cpu".  At what point and for how long should this code pin
itself on a cpu?

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