linux-kernel - Re: [PATCH 4.14 29/45] cgroup/cpuset: remove circular dependency deadlock

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Date:   Wed, 17 Oct 2018 00:16:28 +0530
From:   Amit Pundir <amit.pundir@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        lkml <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Prateek Sood <prsood@...eaurora.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 4.14 29/45] cgroup/cpuset: remove circular dependency deadlock

On Fri, 12 Oct 2018 at 16:35, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Thu, Oct 11, 2018 at 08:33:34PM +0100, Sudip Mukherjee wrote:
> > Hi Greg,
> >
> > On Thu, Oct 11, 2018 at 4:54 PM Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > >
> > > 4.14-stable review patch.  If anyone has any objections, please let me know.
> > >
> > > ------------------
> > >
> > > From: Prateek Sood <prsood@...eaurora.org>
> > >
> > > commit aa24163b2ee5c92120e32e99b5a93143a0f4258e upstream.
> >
> > This has been already reverted in upstream.
> > bdfbbda90aeb ("Revert "cgroup/cpuset: remove circular dependency deadlock"")
> >
> > Might be better to add e8b3f8db7aad ("workqueue/hotplug: simplify
> > workqueue_offline_cpu()") instead which is mentioned in the revert
> > commit.
>
> Good point.  I'm dropping this patch for now.
>
> Amit, can you test the above patch instead and figure out why you wanted
> to add a patch to the tree that ended up being reverted?  :)

Sorry I goofed up here. Thank you Sudip for catching this.

I forgot to look up for the upstream followup fixes for the patches
which I submitted lately and missed out on this Revert.

msm-4.9 tree, which I'm currently looking at, didn't revert this
particular patch either. It did cherry-pick e8b3f8db7aad
("workqueue/hotplug: simplify workqueue_offline_cpu()") as well
though.

About e8b3f8db7aad ("workqueue/hotplug: simplify workqueue_offline_cpu()"):
--------------------------------------------
commit e8b3f8db7aad99fcc5234fc5b89984ff6620de3d
Author: Lai Jiangshan <jiangshanlai@...il.com>
Date:   Fri Dec 1 22:20:36 2017 +0800

    workqueue/hotplug: simplify workqueue_offline_cpu()

    Since the recent cpu/hotplug refactoring, workqueue_offline_cpu() is
    guaranteed to run on the local cpu which is going offline.

    This also fixes the following deadlock by removing work item
    scheduling and flushing from CPU hotplug path.

     http://lkml.kernel.org/r/1504764252-29091-1-git-send-email-prsood@codeaurora.org
--------------------------------------------
This patch applies cleanly to 4.14.y and 4.9.y. But I'm confused if
this particular patch alone is good enough for these stable kernels,
since the commit message talks about some "recent cpu/hotplug
refactoring" dependency(?).

Regards,
Amit Pundir

>
> thanks,
>
> greg k-h
>
> >
> > --
> > Regards
> > Sudip