Commit-ID: f3b577dec1f2ce32d2db6d2ca6badff7002512af
Gitweb: http://git.kernel.org/tip/f3b577dec1f2ce32d2db6d2ca6badff7002512af
Author: Daniel J Blueman <daniel.blueman@xxxxxxxxx>
AuthorDate: Tue, 1 Jun 2010 14:06:13 +0100
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Wed, 23 Jun 2010 06:50:44 -0700
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@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/sched_fair.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index eed35ed..a878b53 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
--
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