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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-06-12 13:30:25 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-07-09 09:15:01 -0700
commitabaa93d9e1de2c29297e69ddba8ddd38f15064cf (patch)
tree127f64c80be6f30fed7265d42cbfc5b449853618 /kernel/rcu/tree_plugin.h
parent48bd8e9b82a750b983823f391c67e70553757afa (diff)
downloadlinux-abaa93d9e1de2c29297e69ddba8ddd38f15064cf.tar.bz2
rcu: Simplify priority boosting by putting rt_mutex in rcu_node
RCU priority boosting currently checks for boosting via a pointer in task_struct. However, this is not needed: As Oleg noted, if the rt_mutex is placed in the rcu_node instead of on the booster's stack, the boostee can simply check it see if it owns the lock. This commit makes this change, shrinking task_struct by one pointer and the kernel by thirteen lines. Suggested-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu/tree_plugin.h')
-rw-r--r--kernel/rcu/tree_plugin.h25
1 files changed, 11 insertions, 14 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 9c811879d31e..719587af7b10 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -33,6 +33,7 @@
#define RCU_KTHREAD_PRIO 1
#ifdef CONFIG_RCU_BOOST
+#include "../locking/rtmutex_common.h"
#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
#else
#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
@@ -336,7 +337,7 @@ void rcu_read_unlock_special(struct task_struct *t)
unsigned long flags;
struct list_head *np;
#ifdef CONFIG_RCU_BOOST
- struct rt_mutex *rbmp = NULL;
+ bool drop_boost_mutex = false;
#endif /* #ifdef CONFIG_RCU_BOOST */
struct rcu_node *rnp;
int special;
@@ -398,11 +399,8 @@ void rcu_read_unlock_special(struct task_struct *t)
#ifdef CONFIG_RCU_BOOST
if (&t->rcu_node_entry == rnp->boost_tasks)
rnp->boost_tasks = np;
- /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
- if (t->rcu_boost_mutex) {
- rbmp = t->rcu_boost_mutex;
- t->rcu_boost_mutex = NULL;
- }
+ /* Snapshot ->boost_mtx ownership with rcu_node lock held. */
+ drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
#endif /* #ifdef CONFIG_RCU_BOOST */
/*
@@ -427,8 +425,8 @@ void rcu_read_unlock_special(struct task_struct *t)
#ifdef CONFIG_RCU_BOOST
/* Unboost if we were boosted. */
- if (rbmp) {
- rt_mutex_unlock(rbmp);
+ if (drop_boost_mutex) {
+ rt_mutex_unlock(&rnp->boost_mtx);
complete(&rnp->boost_completion);
}
#endif /* #ifdef CONFIG_RCU_BOOST */
@@ -1151,7 +1149,6 @@ static void rcu_wake_cond(struct task_struct *t, int status)
static int rcu_boost(struct rcu_node *rnp)
{
unsigned long flags;
- struct rt_mutex mtx;
struct task_struct *t;
struct list_head *tb;
@@ -1202,14 +1199,14 @@ static int rcu_boost(struct rcu_node *rnp)
* section.
*/
t = container_of(tb, struct task_struct, rcu_node_entry);
- rt_mutex_init_proxy_locked(&mtx, t);
- t->rcu_boost_mutex = &mtx;
+ rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
init_completion(&rnp->boost_completion);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
- rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
- rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
+ /* Lock only for side effect: boosts task t's priority. */
+ rt_mutex_lock(&rnp->boost_mtx);
+ rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
- /* Wait until boostee is done accessing mtx before reinitializing. */
+ /* Wait for boostee to be done w/boost_mtx before reinitializing. */
wait_for_completion(&rnp->boost_completion);
return ACCESS_ONCE(rnp->exp_tasks) != NULL ||