Messages in this thread | | | Date | Wed, 1 Nov 2023 13:59:47 -0400 | Subject | Re: [PATCH v2] cgroup/cpuset: Change nr_deadline_tasks to an atomic_t value | From | Waiman Long <> |
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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.
Cheers, Longman
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