[PATCH v3 2/3] sched: Provide copy_user_cpus_mask() to copy out user mask

[Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

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.

Signed-off-by: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 include/linux/sched.h |  1 +
 kernel/sched/core.c   | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index cf7206a9b29a..e06bc1cbccca 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1831,6 +1831,7 @@ extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effec
 extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
 extern int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node);
+extern struct cpumask *copy_user_cpus_mask(struct task_struct *p, struct cpumask *user_mask);
 extern void release_user_cpus_ptr(struct task_struct *p);
 extern int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask);
 extern void force_compatible_cpus_allowed_ptr(struct task_struct *p);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7e2576068331..4d3b10e91e1a 100644
--- 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;
+}
+
 /*
  * This function is wildly self concurrent; here be dragons.
  *
-- 
2.31.1