linux-kernel - [tip: sched/core] sched: Introduce dl_task_check

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Date:   Mon, 23 Aug 2021 09:26:19 -0000
From:   "tip-bot2 for Will Deacon" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Will Deacon <will@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched: Introduce dl_task_check_affinity() to check
 proposed affinity

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     234b8ab6476c5edd5262e2ff563de9498d60044a
Gitweb:        https://git.kernel.org/tip/234b8ab6476c5edd5262e2ff563de9498d60044a
Author:        Will Deacon <will@...nel.org>
AuthorDate:    Fri, 30 Jul 2021 12:24:36 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 20 Aug 2021 12:33:00 +02:00

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@...nel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.com>
Link: https://lore.kernel.org/r/20210730112443.23245-10-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 ce2d5cf..3bb9fec 100644
--- 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
--- 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)