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From: Michael Ellerman <mpe@ellerman.id.au>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	dja@axtens.net, elver@google.com, linux-kernel@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, christophe.leroy@c-s.fr,
	linux-s390@vger.kernel.org, linux-arch@vger.kernel.org,
	x86@kernel.org, kasan-dev@googlegroups.com,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>
Subject: Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)
Date: Wed, 11 Dec 2019 11:29:16 +1100	[thread overview]
Message-ID: <87lfrjpuw3.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20191210101545.GL2844@hirez.programming.kicks-ass.net>

Peter Zijlstra <peterz@infradead.org> writes:
> On Tue, Dec 10, 2019 at 04:38:54PM +1100, Michael Ellerman wrote:
>
>> Good question, I'll have a look.
>> 
>> There seems to be confusion about what the type of the bit number is,
>> which is leading to sign extension in some cases and not others.
>
> Shiny.
>
>> It looks like the type should be unsigned long?
>
> I'm thinking unsigned makes most sense, I mean, negative bit offsets
> should 'work' but that's almost always guaranteed to be an out-of-bound
> operation.

Yeah I agree.

> As to 'long' vs 'int', I'm not sure, 4G bits is a long bitmap. But I
> suppose since the bitmap itself is 'unsigned long', we might as well use
> 'unsigned long' for the bitnr too.

4G is a lot of bits, but it's not *that* many.

eg. If we had a bit per 4K page on a 32T machine that would be 8G bits.

So unsigned long seems best.

>>   Documentation/core-api/atomic_ops.rst:  void __clear_bit_unlock(unsigned long nr, unsigned long *addr);
>>   arch/mips/include/asm/bitops.h:static inline void __clear_bit_unlock(unsigned long nr, volatile unsigned long *addr)
>>   arch/powerpc/include/asm/bitops.h:static inline void arch___clear_bit_unlock(int nr, volatile unsigned long *addr)
>>   arch/riscv/include/asm/bitops.h:static inline void __clear_bit_unlock(unsigned long nr, volatile unsigned long *addr)
>>   arch/s390/include/asm/bitops.h:static inline void arch___clear_bit_unlock(unsigned long nr,
>>   include/asm-generic/bitops/instrumented-lock.h:static inline void __clear_bit_unlock(long nr, volatile unsigned long *addr)
>>   include/asm-generic/bitops/lock.h:static inline void __clear_bit_unlock(unsigned int nr,
>> 
>> So I guess step one is to convert our versions to use unsigned long, so
>> we're at least not tripping over that difference when comparing the
>> assembly.
>
> Yeah, I'll look at fixing the generic code, bitops/atomic.h and
> bitops/non-atomic.h don't even agree on the type of bitnr.

Thanks.

cheers

  reply	other threads:[~2019-12-11  0:29 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-06 12:46 Michael Ellerman
2019-12-06 13:16 ` Peter Zijlstra
2019-12-10  5:38   ` Michael Ellerman
2019-12-10 10:15     ` Peter Zijlstra
2019-12-11  0:29       ` Michael Ellerman [this message]
2019-12-12  5:42   ` READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)) Michael Ellerman
2019-12-12  8:01     ` Peter Zijlstra
2019-12-12 10:07       ` Will Deacon
2019-12-12 10:46         ` Peter Zijlstra
2019-12-12 17:04           ` Will Deacon
2019-12-12 17:16             ` Will Deacon
2019-12-12 17:41           ` Linus Torvalds
2019-12-12 17:50             ` Segher Boessenkool
2019-12-12 18:06             ` Will Deacon
2019-12-12 18:29               ` Christian Borntraeger
2019-12-12 18:43               ` Linus Torvalds
2019-12-12 19:34                 ` Will Deacon
2019-12-12 20:21                   ` Peter Zijlstra
2019-12-12 20:53                     ` Peter Zijlstra
2019-12-13 10:47                       ` Luc Van Oostenryck
2019-12-13 12:56                         ` Peter Zijlstra
2019-12-13 14:28                           ` Luc Van Oostenryck
2019-12-12 20:49                   ` Linus Torvalds
2019-12-13 13:17                     ` Arnd Bergmann
2019-12-13 21:32                       ` Arnd Bergmann
2019-12-13 22:01                         ` Linus Torvalds
2019-12-16 10:28                       ` Will Deacon
2019-12-16 11:47                         ` Peter Zijlstra
2019-12-16 12:06                         ` Arnd Bergmann
2019-12-17 17:07                     ` Will Deacon
2019-12-17 18:04                       ` Linus Torvalds
2019-12-17 18:05                         ` Linus Torvalds
2019-12-17 18:31                           ` Will Deacon
2019-12-17 18:32                         ` Linus Torvalds
2019-12-18 12:17                           ` Michael Ellerman
2019-12-19 12:11                           ` Will Deacon
2019-12-18 10:22                     ` Christian Borntraeger
2019-12-18 10:35                       ` Will Deacon
2019-12-13 12:07           ` Michael Ellerman
2019-12-13 13:53             ` Segher Boessenkool
2019-12-13 21:06               ` Michael Ellerman
2019-12-12 15:10     ` Segher Boessenkool
2019-12-06 22:15 ` [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops) pr-tracker-bot

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