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Message-ID: <20201026171045.GU2611@hirez.programming.kicks-ass.net>
Date: Mon, 26 Oct 2020 18:10:45 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>,
Matthew Wilcox <willy@...radead.org>,
Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
Will Deacon <will.deacon@....com>,
Thomas Gleixner <tglx@...utronix.de>,
Waiman Long <longman@...hat.com>,
Nicholas Piggin <npiggin@...il.com>,
Michael Ellerman <mpe@...erman.id.au>,
Herbert Xu <herbert@...dor.apana.org.au>,
linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] qspinlock: use signed temporaries for cmpxchg
On Mon, Oct 26, 2020 at 05:57:51PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
>
> When building with W=2, the build log is flooded with
>
> include/asm-generic/qrwlock.h:65:56: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
> include/asm-generic/qrwlock.h:92:53: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
> include/asm-generic/qspinlock.h:68:55: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
> include/asm-generic/qspinlock.h:82:52: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
>
> The atomics are built on top of signed integers, but the caller
> doesn't actually care. Just use signed types as well.
>
Yuck, no. This is actively wrong. All that code very much wants u32.
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