linux-kernel - Re: [PATCH v7 1/7] sched/topology: Adding function partition_sched_domains

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Message-ID: <20190405125245.GB5453@localhost.localdomain>
Date:   Fri, 5 Apr 2019 14:52:45 +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
Subject: Re: [PATCH v7 1/7] sched/topology: Adding function
 partition_sched_domains_locked()

Hi,

On 05/04/19 14:04, Peter Zijlstra wrote:
> On Wed, Apr 03, 2019 at 10:46:44AM +0200, Juri Lelli wrote:
> > +/*
> > + * Call with hotplug lock held
> 
> Is that spelled like:
> 
> 	lockdep_assert_cpus_held();
> 
> ?

Indeed, but I had that in previous versions and we removed that in v5
because it can lead to false positives [1,2]. IIRC, problem has to do
with hotplug and the fact that rebuilding from hotplug runs the
callbacks on the newly onlined CPU, not the task that acquired the lock.

Best,

- Juri

1 - https://lore.kernel.org/lkml/20180903142801.20046-1-juri.lelli@redhat.com/
2 - https://lore.kernel.org/lkml/20180613121711.5018-2-juri.lelli@redhat.com/