On Thu, 21 Jan 2016, Michal Hocko wrote:
> It goes like this:
> CPU0: CPU1
> vmstat_update
> cpumask_test_and_set_cpu (0->1)
> [...]
> vmstat_shepherd
> <enter idle> cpumask_test_and_clear_cpu(CPU0) (1->0)
> quiet_vmstat
> cpumask_test_and_set_cpu (0->1)
> queue_delayed_work_on(CPU0)
> refresh_cpu_vm_stats()
> [...]
> vmstat_update
> nothing_to_do
> cpumask_test_and_set_cpu (1->1)
> VM_BUG_ON
>
> Or am I missing something?
Ok then the following should fix it:
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,
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