On Fri 22-01-16 10:46:14, Christoph Lameter wrote: > On Fri, 22 Jan 2016, Michal Hocko wrote: > > > Could you repost the patch with the updated description? > > Subject: vmstat: Remove BUG_ON from vmstat_update > > If we detect that there is nothing to do just set the flag and do not check > if it was already set before. Races really do not matter. If the flag is > set by any code then the shepherd will start dealing with the situation > and reenable the vmstat workers when necessary again. > > Since 0eb77e988032 ("vmstat: make vmstat_updater deferrable again and > shut down on idle") quiet_vmstat might update cpu_stat_off and mark a > particular cpu to be handled by vmstat_shepherd. This might trigger > a VM_BUG_ON in vmstat_update because the work item might have been > sleeping during the idle period and see the cpu_stat_off updated after > the wake up. The VM_BUG_ON is therefore misleading and no more > appropriate. Moreover it doesn't really suite any protection from real > bugs because vmstat_shepherd will simply reschedule the vmstat_work > anytime it sees a particular cpu set or vmstat_update would do the same > from the worker context directly. Even when the two would race the > result wouldn't be incorrect as the counters update is fully idempotent. > Fixes: 0eb77e988032 ("vmstat: make vmstat_updater deferrable again and shut down on idle" Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx> Would be appropriate IMO > Signed-off-by: Christoph Lameter <cl@xxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Thanks! > > Index: linux/mm/vmstat.c > =================================================================== > --- linux.orig/mm/vmstat.c > +++ linux/mm/vmstat.c > @@ -1408,17 +1408,7 @@ static void vmstat_update(struct work_st > * Defer the checking for differentials to the > * shepherd thread on a different processor. > */ > - int r; > - /* > - * Shepherd work thread does not race since it never > - * changes the bit if its zero but the cpu > - * online / off line code may race if > - * worker threads are still allowed during > - * shutdown / startup. > - */ > - r = cpumask_test_and_set_cpu(smp_processor_id(), > - cpu_stat_off); > - VM_BUG_ON(r); > + cpumask_set_cpu(smp_processor_id(), cpu_stat_off); > } > } -- Michal Hocko SUSE Labs -- 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>