From: Daniel J Blueman <daniel.blueman@gmail.com>
Date: Tue, 1 Jun 2010 13:06:13 +0000 (+0100)
Subject: rcu: apply RCU protection to wake_affine()
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=f3b577dec1f2ce32d2db6d2ca6badff7002512af;p=GitHub%2Fexynos8895%2Fandroid_kernel_samsung_universal8895.git

rcu: apply RCU protection to wake_affine()

The task_group() function returns a pointer that must be protected
by either RCU, the ->alloc_lock, or the cgroup lock (see the
rcu_dereference_check() in task_subsys_state(), which is invoked by
task_group()).  The wake_affine() function currently does none of these,
which means that a concurrent update would be within its rights to free
the structure returned by task_group().  Because wake_affine() uses this
structure only to compute load-balancing heuristics, there is no reason
to acquire either of the two locks.

Therefore, this commit introduces an RCU read-side critical section that
starts before the first call to task_group() and ends after the last use
of the "tg" pointer returned from task_group().  Thanks to Li Zefan for
pointing out the need to extend the RCU read-side critical section from
that proposed by the original patch.

Signed-off-by: Daniel J Blueman <daniel.blueman@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index eed35eded602..a878b5332daa 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1240,6 +1240,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
 	 * effect of the currently running task from the load
 	 * of the current CPU:
 	 */
+	rcu_read_lock();
 	if (sync) {
 		tg = task_group(current);
 		weight = current->se.load.weight;
@@ -1275,6 +1276,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
 		balanced = this_eff_load <= prev_eff_load;
 	} else
 		balanced = true;
+	rcu_read_unlock();
 
 	/*
 	 * If the currently running task will sleep within