linux-kernel - Re: [RFC][PATCH 01/31] locking: Flip arguments to atomic_fetch

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Message-ID: <20160422105428.GA10289@arm.com>
Date:	Fri, 22 Apr 2016 11:54:28 +0100
From:	Will Deacon <will.deacon@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	torvalds@...ux-foundation.org, mingo@...nel.org,
	tglx@...utronix.de, paulmck@...ux.vnet.ibm.com,
	boqun.feng@...il.com, waiman.long@....com, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	rth@...ddle.net, vgupta@...opsys.com, linux@....linux.org.uk,
	egtvedt@...fundet.no, realmz6@...il.com,
	ysato@...rs.sourceforge.jp, rkuo@...eaurora.org,
	tony.luck@...el.com, geert@...ux-m68k.org, james.hogan@...tec.com,
	ralf@...ux-mips.org, dhowells@...hat.com, jejb@...isc-linux.org,
	mpe@...erman.id.au, schwidefsky@...ibm.com, dalias@...c.org,
	davem@...emloft.net, cmetcalf@...lanox.com, jcmvbkbc@...il.com,
	arnd@...db.de, dbueso@...e.de, fengguang.wu@...el.com
Subject: Re: [RFC][PATCH 01/31] locking: Flip arguments to atomic_fetch_or

On Fri, Apr 22, 2016 at 11:04:14AM +0200, Peter Zijlstra wrote:
> All the atomic operations have their arguments the wrong way around;
> make atomic_fetch_or() consistent and flip them.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  include/linux/atomic.h   |    4 ++--
>  kernel/time/tick-sched.c |    4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)

Makes sense:

Acked-by: Will Deacon <will.deacon@....com>

Will

> --- a/include/linux/atomic.h
> +++ b/include/linux/atomic.h
> @@ -560,11 +560,11 @@ static inline int atomic_dec_if_positive
>  
>  /**
>   * atomic_fetch_or - perform *p |= mask and return old value of *p
> - * @p: pointer to atomic_t
>   * @mask: mask to OR on the atomic_t
> + * @p: pointer to atomic_t
>   */
>  #ifndef atomic_fetch_or
> -static inline int atomic_fetch_or(atomic_t *p, int mask)
> +static inline int atomic_fetch_or(int mask, atomic_t *p)
>  {
>  	int old, val = atomic_read(p);
>  
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -262,7 +262,7 @@ static void tick_nohz_dep_set_all(atomic
>  {
>  	int prev;
>  
> -	prev = atomic_fetch_or(dep, BIT(bit));
> +	prev = atomic_fetch_or(BIT(bit), dep);
>  	if (!prev)
>  		tick_nohz_full_kick_all();
>  }
> @@ -292,7 +292,7 @@ void tick_nohz_dep_set_cpu(int cpu, enum
>  
>  	ts = per_cpu_ptr(&tick_cpu_sched, cpu);
>  
> -	prev = atomic_fetch_or(&ts->tick_dep_mask, BIT(bit));
> +	prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
>  	if (!prev) {
>  		preempt_disable();
>  		/* Perf needs local kick that is NMI safe */
> 
>