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

From: Arnd Bergmann <arnd@arndb.de>
To: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	kernel-build-reports@lists.linaro.org, olof@lixom.net,
	David Miller <davem@davemloft.net>,
	eric.dumazet@gmail.com, netdev@vger.kernel.org,
	linux-next@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: next build: 235 warnings 3 failures (next/next-20151117)
Date: Tue, 17 Nov 2015 20:17:17 +0100	[thread overview]
Message-ID: <3723928.99NZh1TC6E@wuerfel> (raw)
In-Reply-To: <20151117171236.GJ30101@arm.com>

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