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 <[email protected]> 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,
