linux-kernel - Re: [Linux 5.18-rc1] WARNING: CPU: 1 PID: 0 at kernel/sched/fair.c:3355 update_blocked

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Date:   Tue, 5 Apr 2022 14:21:10 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:     Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [Linux 5.18-rc1] WARNING: CPU: 1 PID: 0 at
 kernel/sched/fair.c:3355 update_blocked_averages

On 04/04/2022 08:19, Ammar Faizi wrote:
> 
> Hello scheduler maintainers,
> 
> I got the following warning in Linux 5.18-rc1, I don't have the
> reproducer yet,
> it happens randomly. Please shed some light.

Tried to recreate the issue but no success so far. I used you config
file, clang-14 and a Xeon CPU E5-2690 v2 (2 sockets 40 CPUs) with 20
two-level cgoupv1 taskgroups '/X/Y' with 'hackbench (10 groups, 40 fds)
+ idling' running in all '/X/Y/'.

What userspace are you running?

There seemed to be some pressure on your machine when it happened?

> <6>[13420.623334][    C7] perf: interrupt took too long (2530 > 2500),
> lowering kernel.perf_event_max_sample_rate to 78900

Maybe you could split the SCHED_WARN_ON so we know which signal causes this?

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d4bd299d67ab..0d45e09e5bfc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3350,9 +3350,9 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq
*cfs_rq)
         * Make sure that rounding and/or propagation of PELT values never
         * break this.
         */
-       SCHED_WARN_ON(cfs_rq->avg.load_avg ||
-                     cfs_rq->avg.util_avg ||
-                     cfs_rq->avg.runnable_avg);
+       SCHED_WARN_ON(cfs_rq->avg.load_avg);
+       SCHED_WARN_ON(cfs_rq->avg.util_avg);
+       SCHED_WARN_ON(cfs_rq->avg.runnable_avg);

        return true;
 }

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