From: Christoph Lameter cl@linux.com
[ Upstream commit 587198ba5206cdf0d30855f7361af950a4172cd6 ]
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 commit 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.
Reported-by: Sasha Levin sasha.levin@oracle.com Signed-off-by: Christoph Lameter cl@linux.com Acked-by: Michal Hocko mhocko@suse.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Cc: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Daniel Wagner wagi@monom.org --- mm/vmstat.c | 12 +----------- 1 file changed, 1 insertion(+), 11 deletions(-)
diff --git a/mm/vmstat.c b/mm/vmstat.c index dd0a13013cb4..233045057a30 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1407,17 +1407,7 @@ static void vmstat_update(struct work_struct *w) * 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); } }