The commit is pushed to "branch-rh8-4.18.0-240.1.1.vz8.5.x-ovz" and will appear
at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-240.1.1.vz8.5.28
------>
commit 9a2e6f0413d5fabfe5c903385e686db3bc852592
Author: Kirill Tkhai <[email protected]>
Date: Thu May 13 16:15:12 2021 +0300
sched: Count loadavg under rq::lock in calc_load_nohz_start()
Since calc_load_fold_active() reads two variables (nr_running
and nr_uninterruptible) it may race with parallel try_to_wake_up().
So it must be executed under rq::lock to prevent that.
This seems to be the reason of negative calc_load_tasks, observed
on several machines.
https://jira.sw.ru/browse/PSBM-68052
Signed-off-by: Kirill Tkhai <[email protected]>
(cherry-picked from vz7 commit 63138412c98b ("sched: Count loadavg under
rq::lock in calc_load_nohz_start()"))
Rebase to vz8:
- move calc_load_migrate under rq lock
- move the rq lock/unlock hunk from calc_load_enter_idle() to
calc_load_nohz_start()
- use rq_(un)lock helpers
like in patch sent to ms https://lkml.org/lkml/2017/7/7/472
This patch did not hit mainstream for some reason but it is likely still
valid, at least I don't see any explicit fix of this problem.
https://jira.sw.ru/browse/PSBM-127780
Signed-off-by: Pavel Tikhomirov <[email protected]>
khorenko@: we don't disable/enable irq in calc_load_nohz_start() because
we assume irqs already disabled in calc_load_nohz_start().
Stack example:
cpuidle_idle_call
tick_nohz_idle_stop_tick
__tick_nohz_idle_stop_tick
tick_nohz_stop_tick
calc_load_nohz_start
---
kernel/sched/core.c | 2 +-
kernel/sched/loadavg.c | 6 +++++-
2 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 375de135c132..3878a91a54b5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6153,9 +6153,9 @@ int sched_cpu_dying(unsigned int cpu)
}
migrate_tasks(rq, &rf);
BUG_ON(rq->nr_running != 1);
+ calc_load_migrate(rq);
rq_unlock_irqrestore(rq, &rf);
- calc_load_migrate(rq);
update_max_interval();
nohz_balance_exit_idle(rq);
hrtick_clear(rq);
diff --git a/kernel/sched/loadavg.c b/kernel/sched/loadavg.c
index c2aab7d55ff2..618682402a3f 100644
--- a/kernel/sched/loadavg.c
+++ b/kernel/sched/loadavg.c
@@ -312,11 +312,15 @@ static void calc_load_nohz_fold(struct rq *rq)
void calc_load_nohz_start(void)
{
+ struct rq *rq = this_rq();
+ struct rq_flags rf;
/*
* We're going into NO_HZ mode, if there's any pending delta, fold it
* into the pending NO_HZ delta.
*/
- calc_load_nohz_fold(this_rq());
+ rq_lock(rq, &rf);
+ calc_load_nohz_fold(rq);
+ rq_unlock(rq, &rf);
}
/*
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