On Thu, Jan 21, 2016 at 11:08 PM, Christoph Lameter <cl@xxxxxxxxx> 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 <cl@xxxxxxxxx> > > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>