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
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