Message-ID: <55410F73.5000807@hp.com>
Date: Wed, 29 Apr 2015 13:05:55 -0400
From: Waiman Long <waiman.long@hp.com>
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To: Jason Low <jason.low2@hp.com>
CC: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, Mel Gorman <mgorman@suse.de>,
        Rik van Riel <riel@redhat.com>, Steven Rostedt <rostedt@goodmis.org>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>,
        Mike Galbraith <umgwanakikbuti@gmail.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Aswin Chandramouleeswaran <aswin@hp.com>,
        Scott J Norton <scott.norton@hp.com>
Subject: Re: [PATCH v2 1/5] sched, timer: Remove usages of ACCESS_ONCE in
 the scheduler
References: <1430251224-5764-1-git-send-email-jason.low2@hp.com> <1430251224-5764-2-git-send-email-jason.low2@hp.com>
In-Reply-To: <1430251224-5764-2-git-send-email-jason.low2@hp.com>
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On 04/28/2015 04:00 PM, Jason Low wrote:
> ACCESS_ONCE doesn't work reliably on non-scalar types. This patch removes
> the rest of the existing usages of ACCESS_ONCE in the scheduler, and use
> the new READ_ONCE and WRITE_ONCE APIs.
>
> Signed-off-by: Jason Low<jason.low2@hp.com>
> ---
>   include/linux/sched.h          |    4 ++--
>   kernel/fork.c                  |    2 +-
>   kernel/sched/auto_group.c      |    2 +-
>   kernel/sched/auto_group.h      |    2 +-
>   kernel/sched/core.c            |    4 ++--
>   kernel/sched/cputime.c         |    2 +-
>   kernel/sched/deadline.c        |    2 +-
>   kernel/sched/fair.c            |   14 +++++++-------
>   kernel/sched/proc.c            |    4 ++--
>   kernel/sched/rt.c              |    2 +-
>   kernel/sched/sched.h           |    2 +-
>   kernel/sched/wait.c            |    4 ++--
>   kernel/time/posix-cpu-timers.c |    8 ++++----
>   13 files changed, 26 insertions(+), 26 deletions(-)
>
> ...
>   		goto no_join;
> @@ -2107,7 +2107,7 @@ void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
>
>   static void reset_ptenuma_scan(struct task_struct *p)
>   {
> -	ACCESS_ONCE(p->mm->numa_scan_seq)++;
> +	WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1);
>   	p->mm->numa_scan_offset = 0;
>   }
>
>

Generally, I am for replacing ACCESS_ONCE() with the more descriptive 
READ_ONCE() and WRITE_ONCE() except the above case where it makes the 
code harder to read without any real advantage.

Other than that,

Acked-by: Waiman Long <Waiman.Long@hp.com>

Cheers,
Longman
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