linux-kernel - Re: [PATCH] sched: fix infinity loop in update_blocked

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Date:   Sun, 30 Dec 2018 13:04:35 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Xie XiuQi <xiexiuqi@...wei.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, xiezhipeng1@...wei.com,
        huawei.libin@...wei.com,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] sched: fix infinity loop in update_blocked_averages


* Vincent Guittot <vincent.guittot@...aro.org> wrote:

> > Reported-by: Zhipeng Xie <xiezhipeng1@...wei.com>
> > Cc: Bin Li <huawei.libin@...wei.com>
> > Cc: <stable@...r.kernel.org>        [4.10+]
> > Fixes: 9c2791f936ef (sched/fair: Fix hierarchical order in rq->leaf_cfs_rq_list)
> 
> If it only happens in update_blocked_averages(), the del leaf has been added by:
> a9e7f6544b9c (sched/fair: Fix O(nr_cgroups) in load balance path)

So I think until we are confident in the proposed fixes, how about 
applying Linus's patch that reverts a9e7f6544b9c and simplifies the list 
manipulation?

That way we can re-introduce the O(nr_cgroups) optimization without 
pressure.

I'll prepare a commit for sched/urgent that does this, please holler if 
any of you disagrees!

Thanks,

	Ingo