Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <1545879866-27809-1-git-send-email-xiexiuqi@huawei.com>
 <CAKfTPtDRGULW3mdFzeyT=OBPdtPsz-6BG-=UGWbK6RQ7Lg8YpA@mail.gmail.com>
 <20181227102107.GA21156@linaro.org> <CAKfTPtD7O_DU5no36jaQziZDCvy=BMJk+tZbnQk2yVt=pzRfPw@mail.gmail.com>
 <CAMp4zn-bN=DdiKox-xZ++i2n_pgTA7Ms+1hBnAY2AbYv2iqXOA@mail.gmail.com>
 <CAKfTPtAmkHZ5XVHpf6rE8nrSPGzW_uO7a0tvH5JqDSpTzK9D=Q@mail.gmail.com>
 <CAHk-=wja7WN1sDz5_E7hf8c47CmX=yH8xc3h0zmmF8Y_fSR71A@mail.gmail.com>
 <20181228011524.GF2509588@devbig004.ftw2.facebook.com> <CAHk-=wj33F7LKQS3wCYJtb_yCzYhbjPzFqhVS_ZPPNOWTTMHFQ@mail.gmail.com>
 <20181228015352.GG2509588@devbig004.ftw2.facebook.com> <20181228020243.GH2509588@devbig004.ftw2.facebook.com>
In-Reply-To: <20181228020243.GH2509588@devbig004.ftw2.facebook.com>
From:   Sargun Dhillon <sargun@sargun.me>
Date:   Fri, 28 Dec 2018 00:38:17 -0500
Message-ID: <CAMp4zn_Nsc58STx+dnzar2+uw=9F3FwSRiK6ZqaBugkcmLk_Xw@mail.gmail.com>
Subject: Re: [PATCH] sched: fix infinity loop in update_blocked_averages
To:     Tejun Heo <tj@kernel.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        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>,
        Dmitry Adamushko <dmitry.adamushko@gmail.com>,
        Rik van Riel <riel@surriel.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Dec 27, 2018 at 9:02 PM Tejun Heo <tj@kernel.org> wrote:
>
> On Thu, Dec 27, 2018 at 05:53:52PM -0800, Tejun Heo wrote:
> > Vincent knows that part way better than me but I think the safest way
> > would be doing the optimization removal iff tmp_alone_branch is
> > already pointing to leaf_cfs_rq_list.  IIUC, it's pointing to
> > something else only while a branch is being built and deferring
> > optimization removal by an avg update cycle isn't gonna make any
> > difference anyway.
>
> So, something like the following.  Xie, can you see whether the
> following patch resolves the problem?
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d1907506318a..88b9118b5191 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7698,7 +7698,8 @@ static void update_blocked_averages(int cpu)
>                  * There can be a lot of idle CPU cgroups.  Don't let fully
>                  * decayed cfs_rqs linger on the list.
>                  */
> -               if (cfs_rq_is_decayed(cfs_rq))
> +               if (cfs_rq_is_decayed(cfs_rq) &&
> +                   rq->tmp_alone_branch == &rq->leaf_cfs_rq_list)
>                         list_del_leaf_cfs_rq(cfs_rq);
>
>                 /* Don't need periodic decay once load/util_avg are null */
Tested-by: Sargun Dhillon <sargun@sargun.me>
We've deployed this patch to our test workload. We haven't seen a crash yet.