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

Waiman Long
2022-08-12T20:39:28Z

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