linux-kernel - [PATCH] sched: don't allow rt_runtime_us to be zero for groups having rt tasks

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Message-ID: <20080227110829.GA15731@linux.vnet.ibm.com>
Date:	Wed, 27 Feb 2008 16:38:29 +0530
From:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ibm.com>,
	Aneesh Kumar KV <aneesh.kumar@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: [PATCH] sched: don't allow rt_runtime_us to be zero for groups
	having rt tasks


This patch checks if we can set the rt_runtime_us to 0. If there is a
realtime task in the group, we don't want to set the rt_runtime_us to 0
otherwise bad things will happen.

Signed-off-by: Dhaval Giani <dhaval@...ux.vnet.ibm.com>
---
 kernel/sched.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+)

Index: linux-2.6.25-rc3/kernel/sched.c
===================================================================
--- linux-2.6.25-rc3.orig/kernel/sched.c
+++ linux-2.6.25-rc3/kernel/sched.c
@@ -7960,6 +7960,17 @@ static int __rt_schedulable(struct task_
 	return total + to_ratio(period, runtime) < global_ratio;
 }
 
+/* Must be called with tasklist_lock held */
+static inline int tg_has_rt_tasks(struct task_group *tg)
+{
+	struct task_struct *p;
+	for_each_process(p) {
+		if (rt_task(p) && rt_rq_of_se(&p->rt)->tg == tg)
+			return 1;
+	}
+	return 0;
+}
+
 int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
 {
 	u64 rt_runtime, rt_period;
@@ -7971,6 +7982,13 @@ int sched_group_set_rt_runtime(struct ta
 		rt_runtime = rt_period;
 
 	mutex_lock(&rt_constraints_mutex);
+	read_lock(&tasklist_lock);
+	if (rt_runtime_us == 0) {
+		if (tg_has_rt_tasks(tg)) {
+			err = -EINVAL;
+			goto unlock;
+		}
+	}
 	if (!__rt_schedulable(tg, rt_period, rt_runtime)) {
 		err = -EINVAL;
 		goto unlock;
@@ -7979,6 +7997,7 @@ int sched_group_set_rt_runtime(struct ta
 		rt_runtime = RUNTIME_INF;
 	tg->rt_runtime = rt_runtime;
  unlock:
+	read_unlock(&tasklist_lock);
 	mutex_unlock(&rt_constraints_mutex);
 
 	return err;
-- 
regards,
Dhaval
--
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