rcu: Simplify unboosting checks

Commit 7765be (Fix RCU_BOOST race handling current->rcu_read_unlock_special)
introduced a new ->rcu_boosted field in the task structure.  This is
redundant because the existing ->rcu_boost_mutex will be non-NULL at
any time that ->rcu_boosted is nonzero.  Therefore, this commit removes
->rcu_boosted and tests ->rcu_boost_mutex instead.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d1a153361749169c020c1ae7294544d97c460659..90b02be2a1655c866fab528567b4cf3d13ab8402 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1259,9 +1259,6 @@ struct task_struct {
 #ifdef CONFIG_PREEMPT_RCU
        int rcu_read_lock_nesting;
        char rcu_read_unlock_special;
-#if defined(CONFIG_RCU_BOOST) && defined(CONFIG_TREE_PREEMPT_RCU)
-       int rcu_boosted;
-#endif /* #if defined(CONFIG_RCU_BOOST) && defined(CONFIG_TREE_PREEMPT_RCU) */
        struct list_head rcu_node_entry;
 #endif /* #ifdef CONFIG_PREEMPT_RCU */
 #ifdef CONFIG_TREE_PREEMPT_RCU

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index ed70f6bf4c31f53d98e65a7a9d340e1c2533699d..eeb38ee8ebbac6cbb59bbfadaa741003d136cab8 100644 (file)
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -306,6 +306,9 @@ static noinline void rcu_read_unlock_special(struct task_struct *t)
        int empty_exp;
        unsigned long flags;
        struct list_head *np;
+#ifdef CONFIG_RCU_BOOST
+       struct rt_mutex *rbmp = NULL;
+#endif /* #ifdef CONFIG_RCU_BOOST */
        struct rcu_node *rnp;
        int special;
 
@@ -351,6 +354,7 @@ static noinline void rcu_read_unlock_special(struct task_struct *t)
                smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
                np = rcu_next_node_entry(t, rnp);
                list_del_init(&t->rcu_node_entry);
+               t->rcu_blocked_node = NULL;
                trace_rcu_unlock_preempted_task("rcu_preempt",
                                                rnp->gpnum, t->pid);
                if (&t->rcu_node_entry == rnp->gp_tasks)
@@ -360,13 +364,12 @@ static noinline 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 and clear ->rcu_boosted with rcu_node lock held. */
-               if (t->rcu_boosted) {
-                       special |= RCU_READ_UNLOCK_BOOSTED;
-                       t->rcu_boosted = 0;
+               /* 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;
                }
 #endif /* #ifdef CONFIG_RCU_BOOST */
-               t->rcu_blocked_node = NULL;
 
                /*
                 * If this was the last task on the current list, and if
@@ -387,10 +390,8 @@ static noinline void rcu_read_unlock_special(struct task_struct *t)
 
 #ifdef CONFIG_RCU_BOOST
                /* Unboost if we were boosted. */
-               if (special & RCU_READ_UNLOCK_BOOSTED) {
-                       rt_mutex_unlock(t->rcu_boost_mutex);
-                       t->rcu_boost_mutex = NULL;
-               }
+               if (rbmp)
+                       rt_mutex_unlock(rbmp);
 #endif /* #ifdef CONFIG_RCU_BOOST */
 
                /*
@@ -1206,7 +1207,6 @@ static int rcu_boost(struct rcu_node *rnp)
        t = container_of(tb, struct task_struct, rcu_node_entry);
        rt_mutex_init_proxy_locked(&mtx, t);
        t->rcu_boost_mutex = &mtx;
-       t->rcu_boosted = 1;
        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. */