On Thu, Aug 23, 2007 at 02:50:38PM -0700, Andrew Morton wrote:
> On Wed, 22 Aug 2007 22:25:51 +0200
> Frederik Deweerdt <[email protected]> wrote:
>
> > On Wed, Aug 22, 2007 at 02:06:48AM -0700, Andrew Morton wrote:
> > >
> > > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.23-rc3/2.6.23-rc3-mm1/
> > >
> > Hi Jeremy,
> >
> > arch/i386/kernel/alternative.c:alternative_instructions() doesn't
> > check for noreplace-smp before setting capability bits and freeing the
> > __smp_locks section.
>
> umm, so? What happens then? What bug is being fixed here, and what are
> its consequences?
That means that even when you specify noreplace_smp, some replacing
takes place anyway. One of the consequences, besides noreplace_smp not
working as expected, is that lguest crashes when you feed it an SMP kernel
(I suspect that you can not replace alternatives for smp _and_ paravirt).
>
> > Every call to alternatives_smp_unlock() checks for noreplace-smp
> > beforehand, so remove the check from there.
> >
> > Boot tested on i386 with UP+noreplace-smp (lguest) and SMP (real hardware)
> >
> > Regards,
> > Frederik
> >
> > Signed-off-by: Frederik Deweerdt <[email protected]>
> >
> > diff --git a/arch/i386/kernel/alternative.c b/arch/i386/kernel/alternative.c
> > index 9f4ac8b..7c5af80 100644
> > --- a/arch/i386/kernel/alternative.c
> > +++ b/arch/i386/kernel/alternative.c
> > @@ -221,9 +221,6 @@ static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end
> > u8 **ptr;
> > char insn[1];
> >
> > - if (noreplace_smp)
> > - return;
> > -
> > add_nops(insn, 1);
> > for (ptr = start; ptr < end; ptr++) {
> > if (*ptr < text)
> > @@ -406,7 +403,7 @@ void __init alternative_instructions(void)
> > #endif
> >
> > #ifdef CONFIG_SMP
> > - if (smp_alt_once) {
> > + if (smp_alt_once && !noreplace_smp) {
> > if (1 == num_possible_cpus()) {
> > printk(KERN_INFO "SMP alternatives: switching to UP code\n");
> > set_bit(X86_FEATURE_UP, boot_cpu_data.x86_capability);
>
> You refer to rc3-mm1 and this is described as a "-mm patch" but it seems to
> also be applicable to mainline?
>
Hmm yes, my bad.
Regards,
Frederik
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