linux-kernel - Re: [tip:sched/core] sched/core: Add debugging code to catch missing update_rq

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Message-ID: <20170130213435.GM31613@codeblueprint.co.uk>
Date:   Mon, 30 Jan 2017 21:34:35 +0000
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     fweisbec@...il.com, tglx@...utronix.de, pmladek@...e.com,
        hpa@...or.com, efault@....de, sergey.senozhatsky.work@...il.com,
        peterz@...radead.org, mgorman@...hsingularity.net,
        wanpeng.li@...mail.com, umgwanakikbuti@...il.com,
        byungchul.park@....com, jack@...e.cz, mingo@...nel.org,
        riel@...hat.com, luca.abeni@...tn.it, yuyang.du@...el.com,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-tip-commits@...r.kernel.org,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: Re: [tip:sched/core] sched/core: Add debugging code to catch missing
 update_rq_clock() calls

On Tue, 31 Jan, at 08:24:53AM, Michael Ellerman wrote:
> 
> I'm hitting this on multiple powerpc systems:
> 
> [   38.339126] rq->clock_update_flags < RQCF_ACT_SKIP
> [   38.339134] ------------[ cut here ]------------
> [   38.339142] WARNING: CPU: 2 PID: 1 at kernel/sched/sched.h:804 detach_task_cfs_rq+0xa0c/0xd10

[...]
 
> I assume I should be worried?

Thanks for the report. No need to worry, the bug has existed for a
while, this patch just turns on the warning ;-)

The following commit queued up in tip/sched/core should fix your
issues (assuming you see the same callstack on all your powerpc
machines):

  https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?h=sched/core&id=1b1d62254df0fe42a711eb71948f915918987790