Re: [PATCH v8 6/8] cgroup/cpuset: Change cpuset_rwsem and hotplug lock order

[Juri Lelli <juri.lelli@redhat.com>]

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@redhat.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