sched: Always clear user_cpus_ptr in do_set_cpus_allowed()

The do_set_cpus_allowed() function is used by either kthread_bind() or
select_fallback_rq(). In both cases the user affinity (if any) should be
destroyed too.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220922180041.1768141-6-longman@redhat.com

kernel/sched/core.c

@@ -2593,14 +2593,20 @@ __do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
 		set_next_task(rq, p);
 }
 
+/*
+ * Used for kthread_bind() and select_fallback_rq(), in both cases the user
+ * affinity (if any) should be destroyed too.
+ */
 void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 {
 	struct affinity_context ac = {
 		.new_mask  = new_mask,
-		.flags     = 0,
+		.user_mask = NULL,
+		.flags     = SCA_USER,	/* clear the user requested mask */
 	};
 
 	__do_set_cpus_allowed(p, &ac);
+	kfree(ac.user_mask);
 }
 
 int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,