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From: Juri Lelli <juri.lelli@redhat.com>
To: Quentin Perret <quentin.perret@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	peterz@infradead.org, mingo@redhat.com,
	linux-kernel@vger.kernel.org, luca.abeni@santannapisa.it,
	claudio@evidence.eu.com, tommaso.cucinotta@santannapisa.it,
	bristot@redhat.com, mathieu.poirier@linaro.org,
	lizefan@huawei.com, cgroups@vger.kernel.org
Subject: Re: [PATCH v4 1/5] sched/topology: Add check to backup comment about hotplug lock
Date: Thu, 14 Jun 2018 16:30:37 +0200	[thread overview]
Message-ID: <20180614143037.GH12032@localhost.localdomain> (raw)
In-Reply-To: <20180614141818.GN17720@e108498-lin.cambridge.arm.com>

On 14/06/18 15:18, Quentin Perret wrote:
> On Thursday 14 Jun 2018 at 16:11:18 (+0200), Juri Lelli wrote:
> > On 14/06/18 14:58, Quentin Perret wrote:
> > 
> > [...]
> > 
> > > Hmm not sure if this can help but I think that rebuild_sched_domains()
> > > does _not_ take the hotplug lock before calling partition_sched_domains()
> > > when CONFIG_CPUSETS=n. But it does take it for CONFIG_CPUSETS=y.
> > 
> > Did you mean cpuset_mutex?
> 
> Nope, I really meant the cpu_hotplug_lock !
> 
> With CONFIG_CPUSETS=n, rebuild_sched_domains() calls
> partition_sched_domains() directly:
> 
> https://elixir.bootlin.com/linux/latest/source/include/linux/cpuset.h#L255
> 
> But with CONFIG_CPUSETS=y, rebuild_sched_domains() calls,
> rebuild_sched_domains_locked(), which calls get_online_cpus() which
> calls cpus_read_lock(), which does percpu_down_read(&cpu_hotplug_lock).
> And all that happens before calling partition_sched_domains().

Ah, right!
 
> So yeah, the point I was trying to make is that there is an inconsistency
> here, maybe for a good reason ? Maybe related to the issue you're seeing ?

The config that came with the 0day splat was indeed CONFIG_CPUSETS=n.

So, in this case IIUC we hit the !doms_new branch of partition_sched_
domains, which uses cpu_active_mask (and cpu_possible_mask indirectly).
Should this be still protected by the hotplug lock then?

  reply	other threads:[~2018-06-14 14:31 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-13 12:17 [PATCH v4 0/5] sched/deadline: fix cpusets bandwidth accounting Juri Lelli
2018-06-13 12:17 ` [PATCH v4 1/5] sched/topology: Add check to backup comment about hotplug lock Juri Lelli
2018-06-14 13:33   ` Steven Rostedt
2018-06-14 13:42     ` Juri Lelli
2018-06-14 13:47       ` Steven Rostedt
2018-06-14 13:50         ` Juri Lelli
2018-06-14 13:58           ` Quentin Perret
2018-06-14 14:11             ` Juri Lelli
2018-06-14 14:18               ` Quentin Perret
2018-06-14 14:30                 ` Juri Lelli [this message]
2018-06-15  8:39                   ` Quentin Perret
2018-06-13 12:17 ` [PATCH v4 2/5] sched/topology: Adding function partition_sched_domains_locked() Juri Lelli
2018-06-14 13:35   ` Steven Rostedt
2018-06-14 13:47     ` Juri Lelli
2018-06-13 12:17 ` [PATCH v4 3/5] sched/core: Streamlining calls to task_rq_unlock() Juri Lelli
2018-06-14 13:42   ` Steven Rostedt
2018-06-13 12:17 ` [PATCH v4 4/5] sched/core: Prevent race condition between cpuset and __sched_setscheduler() Juri Lelli
2018-06-14 13:45   ` Steven Rostedt
2018-06-14 13:51     ` Juri Lelli
2018-06-14 20:11   ` Steven Rostedt
2018-06-15  7:01     ` Juri Lelli
2018-06-15 13:07       ` Juri Lelli
2018-06-13 12:17 ` [PATCH v4 5/5] cpuset: Rebuild root domain deadline accounting information Juri Lelli

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