[PATCH v9 13/20] sched: Introduce dl_task_check_affinity() to check proposed affinity

Will Deacon
2021-06-08T18:04:36Z

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.

Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
include/linux/sched.h | 6 ++++++
kernel/sched/core.c | 46 +++++++++++++++++++++++++++----------------
2 files changed, 35 insertions(+), 17 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 91a6cfeae242..b9d0df8f7153 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1691,6 +1691,7 @@ 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
@@ -1713,6 +1714,11 @@ 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 d3d5e8b33961..d2fe6f8b8f6f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6935,6 +6935,32 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
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)
{
@@ -6952,23 +6978,9 @@ __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)
--
2.32.0.rc1.229.g3e70b5a671-goog