On Thu, Jan 21, 2016 at 11:08 PM, Christoph Lameter <c...@linux.com> wrote:
> Subject: vmstat: Queue work before clearing cpu_stat_off
>
> There is a race between vmstat_shepherd and quiet_vmstat() because
> the responsibility for checking for counter updates changes depending
> on the state of teh bit in cpu_stat_off. So queue the work before
> changing state of the bit in vmstat_shepherd. That way quiet_vmstat
> is guaranteed to remove the work request when clearing the bit and the
> bug in vmstat_update wont trigger anymore.
>
> Signed-off-by: Christoph Lameter <c...@linux.com>
>
> Index: linux/mm/vmstat.c
> ===================================================================
> --- linux.orig/mm/vmstat.c
> +++ linux/mm/vmstat.c
> @@ -1480,12 +1480,14 @@ static void vmstat_shepherd(struct work_
> get_online_cpus();
> /* Check processors whose vmstat worker threads have been disabled */
> for_each_cpu(cpu, cpu_stat_off)
> - if (need_update(cpu) &&
> - cpumask_test_and_clear_cpu(cpu, cpu_stat_off))
> + if (need_update(cpu)) {
>
> queue_delayed_work_on(cpu, vmstat_wq,
> &per_cpu(vmstat_work, cpu), 0);
>
> + cpumask_clear_cpu(smp_processor_id(), cpu_stat_off);
> + }
> +
> put_online_cpus();
>
> schedule_delayed_work(&shepherd,
This can alternatively lead to following where vmstat may not be
scheduled for cpu when it is back from idle.
CPU0: CPU1:
vmstat_shepherd
<enter idle> queue_delayed_work_on(CPU0)
quiet_vmstat
cancel_delayed_work
cpumask_test_and_set_cpu (0->1)
cpumask_clear_cpu(CPU0) (1->0)
--
regards
Shiraz Hashim
