Re: [PATCH v2 1/5] sched, timer: Remove usages of ACCESS_ONCE in the scheduler

Waiman Long
2015-04-29T17:06:05Z

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