Subject: Re: next build: 235 warnings 3 failures (next/next-20151117)

From: Will Deacon <[email-masked]>
Date: Wed, 18 Nov 2015 10:14:28 +0000

On Tue, Nov 17, 2015 at 08:17:17PM +0100, Arnd Bergmann wrote:
> On Tuesday 17 November 2015 17:12:37 Will Deacon wrote:
> > On Tue, Nov 17, 2015 at 06:03:40PM +0100, Arnd Bergmann wrote:
> > > On Tuesday 17 November 2015 16:44:53 Will Deacon wrote:
> > > > > 8<----
> > > > > Subject: ARM64: make smp_load_acquire() work with const arguments
> > > > > 
> > > > > smp_load_acquire() uses typeof() to declare a local variable for temporarily
> > > > > storing the output of the memory access. This fails when the argument is
> > > > > constant, because the assembler complains about using a constant register
> > > > > as output:
> > > > > 
> > > > >  arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1'
> > > > >  used as 'asm' output
> > > > 
> > > > Do you know the usage in the kernel causing this warning?
> > > 
> > > A newly introduced function in include/net/sock.h:
> > > 
> > > static inline int sk_state_load(const struct sock *sk)
> > > {
> > >         return smp_load_acquire(&sk->sk_state);
> > > }
> > 
> > Hmm, maybe we could play a similar trick to READ_ONCE by declaring an
> > anonymous union and writing through the non-const member?
> 
> Yes, I think that would work, if you think we need to care about the
> case where we read into a structure.
> 
> Can you come up with a patch for that?

Done:

  http://lists.infradead.org/pipermail/linux-arm-kernel/2015-November/386094.html

Will