Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 2 Nov 2023 11:26:39 +0100 | From | Juri Lelli <> | Subject | Re: [PATCH v2] cgroup/cpuset: Change nr_deadline_tasks to an atomic_t value |
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Hi Waiman,
On 01/11/23 13:59, Waiman Long wrote: > On 11/1/23 12:34, Michal Koutný wrote: > > On Tue, Oct 24, 2023 at 10:18:34AM -0400, Waiman Long <longman@redhat.com> wrote: > > > The nr_deadline_tasks field in cpuset structure was introduced by > > > commit 6c24849f5515 ("sched/cpuset: Keep track of SCHED_DEADLINE task > > > in cpusets"). Unlike nr_migrate_dl_tasks which is only modified under > > > cpuset_mutex, nr_deadline_tasks can be updated under two different > > > locks - cpuset_mutex in most cases or css_set_lock in cgroup_exit(). As > > > a result, data races can happen leading to incorrect nr_deadline_tasks > > > value. > > The effect is that dl_update_tasks_root_domain() processes tasks > > unnecessarily or that it incorrectly skips dl_add_task_root_domain()? > The effect is that dl_update_tasks_root_domain() may return incorrectly or > it is doing unnecessary work. Will update the commit log to reflect that. > > > > > Since it is not practical to somehow take cpuset_mutex in cgroup_exit(), > > > the easy way out to avoid this possible race condition is by making > > > nr_deadline_tasks an atomic_t value. > > If css_set_lock is useless for this fields and it's going to be atomic, > > could you please add (presumably) a cleanup that moves dec_dl_tasks_cs() > > from under css_set_lock in cgroup_exit() to a (new but specific) > > cpuset_cgrp_subsys.exit() handler? > > But css_set_lock is needed for updating other css data. It is true that we > can move dec_dl_tasks_cs() outside of the lock. I can do that in the next > version.
Not sure if you had a chance to check my last question/comment on your previous posting?
https://lore.kernel.org/lkml/ZSjfBWgZf15TchA5@localhost.localdomain/
Thanks, Juri
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