sched: more sanity checks on the bandwidth settings

While playing around with it, I noticed we missed some sanity checks.
Also add some comments while we're there.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 28 insertions, 5 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 669c49aa57f0..e1299de1765e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8866,11 +8866,29 @@ static int tg_schedulable(struct task_group *tg, void *data)
                 runtime = d->rt_runtime;
         }
 
+        /*
+         * Cannot have more runtime than the period.
+         */
+        if (runtime > period && runtime != RUNTIME_INF)
+                return -EINVAL;
+
+        /*
+         * Ensure we don't starve existing RT tasks.
+         */
         if (rt_bandwidth_enabled() && !runtime && tg_has_rt_tasks(tg))
                 return -EBUSY;
 
         total = to_ratio(period, runtime);
 
+        /*
+         * Nobody can have more than the global setting allows.
+         */
+        if (total > to_ratio(global_rt_period(), global_rt_runtime()))
+                return -EINVAL;
+
+        /*
+         * The sum of our children's runtime should not exceed our own.
+         */
         list_for_each_entry_rcu(child, &tg->children, siblings) {
                 period = ktime_to_ns(child->rt_bandwidth.rt_period);
                 runtime = child->rt_bandwidth.rt_runtime;
@@ -8978,19 +8996,24 @@ long sched_group_rt_period(struct task_group *tg)
 
 static int sched_rt_global_constraints(void)
 {
-        struct task_group *tg = &root_task_group;
-        u64 rt_runtime, rt_period;
+        u64 runtime, period;
         int ret = 0;
 
         if (sysctl_sched_rt_period <= 0)
                 return -EINVAL;
 
-        rt_period = ktime_to_ns(tg->rt_bandwidth.rt_period);
-        rt_runtime = tg->rt_bandwidth.rt_runtime;
+        runtime = global_rt_runtime();
+        period = global_rt_period();
+
+        /*
+         * Sanity check on the sysctl variables.
+         */
+        if (runtime > period && runtime != RUNTIME_INF)
+                return -EINVAL;
 
         mutex_lock(&rt_constraints_mutex);
         read_lock(&tasklist_lock);
-        ret = __rt_schedulable(tg, rt_period, rt_runtime);
+        ret = __rt_schedulable(NULL, 0, 0);
         read_unlock(&tasklist_lock);
         mutex_unlock(&rt_constraints_mutex);