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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Sun, 30 Dec 2018 13:36:25 +0100
Message-ID: <CAKfTPtA2ibYVJdqdWbEVjjCYueSCzc15Jwt9RNo=D=3kUFpEFw@mail.gmail.com>
Subject: Re: [PATCH] sched: fix infinity loop in update_blocked_averages
To:     Ingo Molnar <mingo@kernel.org>
Cc:     Xie XiuQi <xiexiuqi@huawei.com>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, xiezhipeng1@huawei.com,
        huawei.libin@huawei.com,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>
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On Sun, 30 Dec 2018 at 13:04, Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Vincent Guittot <vincent.guittot@linaro.org> wrote:
>
> > > Reported-by: Zhipeng Xie <xiezhipeng1@huawei.com>
> > > Cc: Bin Li <huawei.libin@huawei.com>
> > > Cc: <stable@vger.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?

looks good to me

Thanks
Vincent
>
> 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