linux-kernel - Re: [PATCH 06/16] ia64: fix up obsolete cpu function usage.

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Message-ID: <87lhg9welh.fsf@rustcorp.com.au>
Date:	Thu, 28 May 2015 13:14:26 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Tony Luck <tony.luck@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Fenghua Yu <fenghua.yu@...el.com>,
	"linux-ia64\@vger.kernel.org" <linux-ia64@...r.kernel.org>
Subject: Re: [PATCH 06/16] ia64: fix up obsolete cpu function usage.

Tony Luck <tony.luck@...il.com> writes:
> On Tue, May 26, 2015 at 6:18 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
>
>> cpumask_test_cpu() doesn't take volatile, unlike the obsoleted
>> cpu_isset.  The only place ia64 really cares is the spin waiting for a
>> bit; udelay() is probably a barrier but insert rmb() to be sure.
>
> Good to be sure ... but cpumask_test_cpu() simply calls test_bit() ...
> and 2 out of 3 versions of that function throw "volatile" back into the
> mix: :-)

Yep, volatile is hard to remove.  But that seems like an argument for
removing the last user, not changing the interface...

The theory is that we're eschewing volatile, or so I thought.

Cheers,
Rusty.

> Global definition: test_bit
>
>   File                            Line
> 0 include/asm/bitops.h            334 test_bit (int nr, const volatile
> void *addr)
> 1 asm-generic/bitops/non-atomic.h 103 static inline int test_bit(int
> nr, const volatile unsigned long *addr)
> 2 asm-generic/bitops/atomic.h      16 static __always_inline int
> test_bit(unsigned int nr, const unsigned long *addr)
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