sched: Introduce dl_task_check_affinity() to check proposed affinity

In preparation for restricting the affinity of a task during execve()
on arm64, introduce a new dl_task_check_affinity() helper function to
give an indication as to whether the restricted mask is admissible for
a deadline task.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Link: https://lore.kernel.org/r/20210730112443.23245-10-will@kernel.org

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ce2d5cf..3bb9fec 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1709,6 +1709,7 @@ extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new
 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 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);
 extern void relax_compatible_cpus_allowed_ptr(struct task_struct *p);
 #else
@@ -1731,6 +1732,11 @@ static inline void release_user_cpus_ptr(struct task_struct *p)
 {
        WARN_ON(p->user_cpus_ptr);
 }
+
+static inline int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
+{
+       return 0;
+}
 #endif
 
 extern int yield_to(struct task_struct *p, bool preempt);

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6ee1970..a22cc3c 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7756,6 +7756,32 @@ out_unlock:
        return retval;
 }
 
+#ifdef CONFIG_SMP
+int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
+{
+       int ret = 0;
+
+       /*
+        * If the task isn't a deadline task or admission control is
+        * disabled then we don't care about affinity changes.
+        */
+       if (!task_has_dl_policy(p) || !dl_bandwidth_enabled())
+               return 0;
+
+       /*
+        * Since bandwidth control happens on root_domain basis,
+        * if admission test is enabled, we only admit -deadline
+        * tasks allowed to run on all the CPUs in the task's
+        * root_domain.
+        */
+       rcu_read_lock();
+       if (!cpumask_subset(task_rq(p)->rd->span, mask))
+               ret = -EBUSY;
+       rcu_read_unlock();
+       return ret;
+}
+#endif
+
 static int
 __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
 {
@@ -7773,23 +7799,9 @@ __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
        cpuset_cpus_allowed(p, cpus_allowed);
        cpumask_and(new_mask, mask, cpus_allowed);
 
-       /*
-        * Since bandwidth control happens on root_domain basis,
-        * if admission test is enabled, we only admit -deadline
-        * tasks allowed to run on all the CPUs in the task's
-        * root_domain.
-        */
-#ifdef CONFIG_SMP
-       if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
-               rcu_read_lock();
-               if (!cpumask_subset(task_rq(p)->rd->span, new_mask)) {
-                       retval = -EBUSY;
-                       rcu_read_unlock();
-                       goto out_free_new_mask;
-               }
-               rcu_read_unlock();
-       }
-#endif
+       retval = dl_task_check_affinity(p, new_mask);
+       if (retval)
+               goto out_free_new_mask;
 again:
        retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK | SCA_USER);
        if (retval)