sched: Use dl_bw_of() under RCU read lock

commit 66339c31 upstream.

dl_bw_of() dereferences rq->rd which has to have RCU read lock held.
Probability of use-after-free isn't zero here.

Also add lockdep assert into dl_bw_cpus().
Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140922183624.11015.71558.stgit@localhostSigned-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

kernel/sched/core.c

@@ -1969,6 +1969,8 @@ unsigned long to_ratio(u64 period, u64 runtime)
 #ifdef CONFIG_SMP
 inline struct dl_bw *dl_bw_of(int i)
 {
+	rcu_lockdep_assert(rcu_read_lock_sched_held(),
+			   "sched RCU must be held");
 	return &cpu_rq(i)->rd->dl_bw;
 }
 
@@ -1977,6 +1979,8 @@ static inline int dl_bw_cpus(int i)
 	struct root_domain *rd = cpu_rq(i)->rd;
 	int cpus = 0;
 
+	rcu_lockdep_assert(rcu_read_lock_sched_held(),
+			   "sched RCU must be held");
 	for_each_cpu_and(i, rd->span, cpu_active_mask)
 		cpus++;
 
@@ -7541,6 +7545,8 @@ static int sched_dl_global_constraints(void)
 	int cpu, ret = 0;
 	unsigned long flags;
 
+	rcu_read_lock();
+
 	/*
 	 * Here we want to check the bandwidth not being set to some
 	 * value smaller than the currently allocated bandwidth in
@@ -7562,6 +7568,8 @@ static int sched_dl_global_constraints(void)
 			break;
 	}
 
+	rcu_read_unlock();
+
 	return ret;
 }
 
@@ -7577,6 +7585,7 @@ static void sched_dl_do_global(void)
 	if (global_rt_runtime() != RUNTIME_INF)
 		new_bw = to_ratio(global_rt_period(), global_rt_runtime());
 
+	rcu_read_lock();
 	/*
 	 * FIXME: As above...
 	 */
@@ -7587,6 +7596,7 @@ static void sched_dl_do_global(void)
 		dl_b->bw = new_bw;
 		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 	}
+	rcu_read_unlock();
 }
 
 static int sched_rt_global_validate(void)