linux-kernel - Re: [PATCH v8 6/8] cgroup/cpuset: Change cpuset

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Date:   Mon, 1 Jul 2019 08:52:33 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, rostedt@...dmis.org, tj@...nel.org,
        linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, mathieu.poirier@...aro.org, lizefan@...wei.com,
        cgroups@...r.kernel.org, Prateek Sood <prsood@...eaurora.org>
Subject: Re: [PATCH v8 6/8] cgroup/cpuset: Change cpuset_rwsem and hotplug
 lock order

Hi,

On 28/06/19 15:03, Peter Zijlstra wrote:
> On Fri, Jun 28, 2019 at 10:06:16AM +0200, Juri Lelli wrote:
> > cpuset_rwsem is going to be acquired from sched_setscheduler() with a
> > following patch. There are however paths (e.g., spawn_ksoftirqd) in
> > which sched_scheduler() is eventually called while holding hotplug lock;
> > this creates a dependecy between hotplug lock (to be always acquired
> > first) and cpuset_rwsem (to be always acquired after hotplug lock).
> > 
> > Fix paths which currently take the two locks in the wrong order (after
> > a following patch is applied).
> > Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
> 
> This all reminds me of this:
> 
>   https://lkml.kernel.org/r/1510755615-25906-1-git-send-email-prsood@codeaurora.org
> 
> Which sadly got reverted again. If we do this now (I've always been a
> proponent), then we can make that rebuild synchronous again, which
> should also help here IIRC.

Why was that reverted? Perf regression of some type?

Thanks,

Juri