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From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] sched/fair: initialize throttle_count for new task-groups lazily
Date: Wed, 22 Jun 2016 11:10:46 +0300
Message-ID: <576A4806.3090701@yandex-team.ru> (raw)
In-Reply-To: <20160621211054.GV30154@twins.programming.kicks-ass.net>

On 22.06.2016 00:10, Peter Zijlstra wrote:
> On Thu, Jun 16, 2016 at 03:57:01PM +0300, Konstantin Khlebnikov wrote:
>> Cgroup created inside throttled group must inherit current throttle_count.
>> Broken throttle_count allows to nominate throttled entries as a next buddy,
>> later this leads to null pointer dereference in pick_next_task_fair().
>>
>> This patch initialize cfs_rq->throttle_count at first enqueue: laziness
>> allows to skip locking all rq at group creation. Lazy approach also allows
>> to skip full sub-tree scan at throttling hierarchy (not in this patch).
>
> You're talking about taking rq->lock in alloc_fair_sched_group(), right?
>
> We're about to go do that anyway... But I suppose for backports this
> makes sense. Doing it at creation time also avoids the issues Ben
> raised, right?

Yes, all will be fine. But for 8192-cores this will be disaster =)
throttle_count must be initialized after linking tg into lists. obviously.

-- 
Konstantin

  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-16 12:57 Konstantin Khlebnikov
2016-06-16 17:03 ` bsegall
2016-06-16 17:23   ` Konstantin Khlebnikov
2016-06-16 17:33     ` bsegall
2016-06-21 13:41 ` Konstantin Khlebnikov
2016-06-21 21:10 ` Peter Zijlstra
2016-06-22  8:10   ` Konstantin Khlebnikov [this message]
2016-06-22  8:23     ` Peter Zijlstra
2016-06-24  8:59 ` [tip:sched/urgent] sched/fair: Initialize " tip-bot for Konstantin Khlebnikov

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