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.
Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
include/linux/sched.h | 1 +
kernel/sched/core.c | 19 +++++++++++++++++++
2 files changed, 20 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index e7b2f8a5c711..f2b0340c094e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1830,6 +1830,7 @@ 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 03053eebb22e..a0987784913e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2618,6 +2618,25 @@ 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.
+ * Acquiring pi_lock for read access protection.
+ */
+struct cpumask *copy_user_cpus_mask(struct task_struct *p,
+ struct cpumask *user_mask)
+{
+ struct cpumask *mask = NULL;
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&p->pi_lock, flags);
+ if (p->user_cpus_ptr) {
+ cpumask_copy(user_mask, p->user_cpus_ptr);
+ mask = user_mask;
+ }
+ raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+ return mask;
+}
+
/*
* This function is wildly self concurrent; here be dragons.
*
--
2.31.1
