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

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Message-ID: <3723928.99NZh1TC6E@wuerfel>
Date:	Tue, 17 Nov 2015 20:17:17 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Will Deacon <will.deacon@....com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	kernel-build-reports@...ts.linaro.org, olof@...om.net,
	David Miller <davem@...emloft.net>, eric.dumazet@...il.com,
	netdev@...r.kernel.org, linux-next@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: next build: 235 warnings 3 failures (next/next-20151117)

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?

	Arnd
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