From f3b577dec1f2ce32d2db6d2ca6badff7002512af Mon Sep 17 00:00:00 2001 From: Daniel J Blueman Date: Tue, 1 Jun 2010 14:06:13 +0100 Subject: [PATCH] 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 Signed-off-by: Paul E. McKenney --- kernel/sched_fair.c | 2 ++ 1 file changed, 2 insertions(+) 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 -- GitLab