In the Linux kernel, the following vulnerability has been resolved: cgroup/cpuset: Make nr_deadline_tasks an atomic_t The nr_deadline_task

In the Linux kernel, the following vulnerability has been resolved:

cgroup/cpuset: Make nr_deadline_tasks an atomic_t

The nr_deadline_tasks variable in the cpuset structure was introduced by
commit 6c24849f5515 ("sched/cpuset: Keep track of SCHED_DEADLINE task
in cpusets"). It is reported by sashiko [1] that nr_deadline_tasks
can currently be modified by inc_dl_tasks_cs() under rq->lock and
by cpuset_attach() under cpuset_mutex. So if both updates happen
simultaneously, the nr_deadline_tasks variable can be corrupted leading
to incorrect operations down the road.

Fix that by changing its type to atomic_t so that nr_deadline_tasks
are always atomically updated. This fix patch is a low hanging fruit.
It can handle some of the races between a concurrent sched_setscheduler()
and cpuset_can_attach()/cpuset_attach() calls, but not all of them like
the other issue raised by sashiko [2]. This will be handled hopefully
in a future follow up patch.

[1] https://sashiko.dev/#/patchset/20260626181923.133658-1-longman%40redhat.com
[2] https://sashiko.dev/#/patchset/20260630033344.352702-1-longman%40redhat.com