* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> How does this work for you at all?
> 
> On Fri, Feb 20, 2015 at 5:37 AM, Ingo Molnar <mingo@kernel.org> wrote:
> > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > index 94f643484300..e354cc6446ab 100644
> > --- a/arch/x86/kernel/kvm.c
> > +++ b/arch/x86/kernel/kvm.c
> > @@ -803,8 +808,8 @@ static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
> >         add_stats(RELEASED_SLOW, 1);
> >         for_each_cpu(cpu, &waiting_cpus) {
> >                 const struct kvm_lock_waiting *w = &per_cpu(klock_waiting, cpu);
> > -               if (ACCESS_ONCE(w->lock) == lock &&
> > -                   ACCESS_ONCE(w->want) == ticket) {
> > +               if (READ_ONCE(w->lock) == lock &&
> > +                   READ_ONCE(w->want) == ticket) {
> >                         add_stats(RELEASED_SLOW_KICKED, 1);
> >                         kvm_kick_cpu(cpu);
> >                         break;
> 
> I get horrible compile warnings from this, because of how 
> 'w' is a pointer to a 'const' structure, which then 
> causes things like
> 
>     include/linux/compiler.h:262:39: warning: passing argument 1 of
> ‘__read_once_size’ discards ‘const’ qualifier from pointer target type
>       ({ typeof(x) __val; __read_once_size(&x, &__val, sizeof(__val)); __val; })
> 
> which is fairly hard to avoid (looks like it might need a 
> union)

Hm, that's really weird, I got no kernel build warnings at 
any stage during handling this commit, and I tested 
d6abfdb20223 for warnings right before sending you the pull 
request, as I do with every pull request, and booted the 
image as well.

( I've attached the build log that I saw before sending you 
  the pull request. )

The kbuild test robot which tests for warnings didn't 
report one to me either. I tested a few other configs as 
well:

  x86 defconfig (PARAVIRT=n):        0 warnings
  'make kvmconfig' (PARAVIRT=y):     0 warnings
  x86 bootable config (attached):    0 warnings

That's with a distro compiler with a couple of months old 
package: gcc version 4.8.3 20140911.

Could that warning be somehow config or compiler dependent? 
Could you send me your .config?

Weird and obviously annoying.

Thanks,

	Ingo