linux-kernel - Re: [PATCH 27/33] locking/atomic: powerpc: move to ARCH

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Message-ID: <20210511091621.GA6152@C02TD0UTHF1T.local>
Date:   Tue, 11 May 2021 10:16:21 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org, will@...nel.org,
        boqun.feng@...il.com, peterz@...radead.org
Cc:     aou@...s.berkeley.edu, arnd@...db.de, bcain@...eaurora.org,
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        davem@...emloft.net, deanbo422@...il.com, deller@....de,
        geert@...ux-m68k.org, green.hu@...il.com, guoren@...nel.org,
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        ysato@...rs.sourceforge.jp
Subject: Re: [PATCH 27/33] locking/atomic: powerpc: move to ARCH_ATOMIC

On Mon, May 10, 2021 at 10:37:47AM +0100, Mark Rutland wrote:
> We'd like all architectures to convert to ARCH_ATOMIC, as once all
> architectures are converted it will be possible to make significant
> cleanups to the atomics headers, and this will make it much easier to
> generically enable atomic functionality (e.g. debug logic in the
> instrumented wrappers).
> 
> As a step towards that, this patch migrates powerpc to ARCH_ATOMIC. The
> arch code provides arch_{atomic,atomic64,xchg,cmpxchg}*(), and common
> code wraps these with optional instrumentation to provide the regular
> functions.
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Will Deacon <will@...nel.org>
> ---
>  arch/powerpc/Kconfig               |   1 +
>  arch/powerpc/include/asm/atomic.h  | 140 +++++++++++++++++++------------------
>  arch/powerpc/include/asm/cmpxchg.h |  30 ++++----
>  3 files changed, 89 insertions(+), 82 deletions(-)

The kbuild test robot spotted a couple of bits I'd got wrong; I've noted
those below (and both are now fixed in my kernel.org branch).

>  static __always_inline bool
> -atomic_try_cmpxchg_lock(atomic_t *v, int *old, int new)
> +arch_atomic_try_cmpxchg_lock(atomic_t *v, int *old, int new)

Since this isn't part of the core atomic API, and is used directly by
powerpc's spinlock implementation, this should have stayed as-is (or we
should use the `arch_` prefix consitently and update the spinlock code).

I've dropped the `arch_` prefix for now.

[...]

>  /**
>   * atomic64_fetch_add_unless - add unless the number is a given value
> @@ -518,7 +524,7 @@ static __inline__ s64 atomic64_dec_if_positive(atomic64_t *v)
>   * Atomically adds @a to @v, so long as it was not @u.
>   * Returns the old value of @v.
>   */
> -static __inline__ s64 atomic64_fetch_add_unless(atomic64_t *v, s64 a, s64 u)
> +static __inline__ s64 arch_atomic64_fetch_add_unless(atomic64_t *v, s64 a, s64 u)
>  {
>  	s64 t;
>  
> @@ -539,7 +545,7 @@ static __inline__ s64 atomic64_fetch_add_unless(atomic64_t *v, s64 a, s64 u)
>  
>  	return t;
>  }
> -#define atomic64_fetch_add_unless atomic64_fetch_add_unless
> +#define arch_atomic64_fetch_add_unless atomic64_fetch_add_unless

Looks like I forgot the `arch_` prefix on the right hand side here; this
should have been:

#define arch_atomic64_fetch_add_unless arch_atomic64_fetch_add_unless

Thanks,
Mark.