On 8/15/22 04:58, Peter Zijlstra wrote:
On Fri, Aug 12, 2022 at 04:39:28PM -0400, Waiman Long wrote:
Since accessing the content of the user_cpus_ptr requires lock protection
to ensure its validity, provide a helper function copy_user_cpus_mask()
to facilitate its reading.
Sure, but this is atrocious.
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2619,6 +2619,24 @@ void release_user_cpus_ptr(struct task_struct *p)
kfree(clear_user_cpus_ptr(p));
}
+/*
+ * Return the copied mask pointer or NULL if user mask not available.
+ */
+struct cpumask *copy_user_cpus_mask(struct task_struct *p,
+ struct cpumask *user_mask)
+{
+ struct rq_flags rf;
+ struct rq *rq = task_rq_lock(p, &rf);
+ struct cpumask *mask = NULL;
+
+ if (p->user_cpus_ptr) {
+ cpumask_copy(user_mask, p->user_cpus_ptr);
+ mask = user_mask;
+ }
+ task_rq_unlock(rq, p, &rf);
+ return mask;
+}
For reading the mask you only need one of those locks, and I would
suggest p->pi_lock is much less contended than rq->lock.
Right. pi_lock should be enough for read access. Will make the change.
Thanks,
Longman
