From 0b88f2ba7caa2d0ff6e3521481a82be084ecdc7b Mon Sep 17 00:00:00 2001 From: Daniel J Blueman Date: Tue, 1 Jun 2010 14:06:13 +0100 Subject: [PATCH] sched: apply RCU protection to wake_affine() commit f3b577dec1f2ce32d2db6d2ca6badff7002512af upstream 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 Signed-off-by: Mike Galbraith Signed-off-by: Greg Kroah-Hartman --- kernel/sched_fair.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index d2c46e761fcd..15a3182baeff 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -1250,6 +1250,7 @@ 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_load || 100*(this_load + effective_load(tg, this_cpu, weight, weight)) <= imbalance*(load + effective_load(tg, prev_cpu, 0, weight)); + rcu_read_unlock(); /* * If the currently running task will sleep within -- 2.34.1