linux-kernel - Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg

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Message-ID: <20160315110633.GV6344@twins.programming.kicks-ass.net>
Date:	Tue, 15 Mar 2016 12:06:33 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to
 'xchg_or()'

On Tue, Mar 15, 2016 at 10:32:45AM +0100, Ingo Molnar wrote:
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 969e6704c3c9..851631899352 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -264,7 +264,7 @@ static void tick_nohz_dep_set_all(unsigned long *dep,
>  {
>  	unsigned long prev;
>  
> -	prev = fetch_or(dep, BIT_MASK(bit));
> +	prev = xchg_or(dep, BIT_MASK(bit));
>  	if (!prev)
>  		tick_nohz_full_kick_all();
>  }
> @@ -294,7 +294,7 @@ void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
>  
>  	ts = per_cpu_ptr(&tick_cpu_sched, cpu);
>  
> -	prev = fetch_or(&ts->tick_dep_mask, BIT_MASK(bit));
> +	prev = xchg_or(&ts->tick_dep_mask, BIT_MASK(bit));
>  	if (!prev) {
>  		preempt_disable();
>  		/* Perf needs local kick that is NMI safe */

Those should probably also use BIT(), BIT_MASK() is specifically for
bitmasks, and should be combined with BIT_WORD().