rcu: refactor RCU's context-switch handling

[safe/jmp/linux-2.6] / kernel / rcutree_plugin.h

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 687c4e9..f9bc83a 100644 (file)
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -75,13 +75,19 @@ EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
  * that this just means that the task currently running on the CPU is
  * not in a quiescent state.  There might be any number of tasks blocked
  * while in an RCU read-side critical section.
+ *
+ * Unlike the other rcu_*_qs() functions, callers to this function
+ * must disable irqs in order to protect the assignment to
+ * ->rcu_read_unlock_special.
  */
 static void rcu_preempt_qs(int cpu)
 {
        struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
+
        rdp->passed_quiesc_completed = rdp->gpnum - 1;
        barrier();
        rdp->passed_quiesc = 1;
+       current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
 }
 
 /*
@@ -144,9 +150,8 @@ static void rcu_preempt_note_context_switch(int cpu)
         * grace period, then the fact that the task has been enqueued
         * means that we continue to block the current grace period.
         */
-       rcu_preempt_qs(cpu);
        local_irq_save(flags);
-       t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
+       rcu_preempt_qs(cpu);
        local_irq_restore(flags);
 }
 
@@ -236,7 +241,6 @@ static void rcu_read_unlock_special(struct task_struct *t)
         */
        special = t->rcu_read_unlock_special;
        if (special & RCU_READ_UNLOCK_NEED_QS) {
-               t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
                rcu_preempt_qs(smp_processor_id());
        }
 
@@ -473,7 +477,6 @@ static void rcu_preempt_check_callbacks(int cpu)
        struct task_struct *t = current;
 
        if (t->rcu_read_lock_nesting == 0) {
-               t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
                rcu_preempt_qs(cpu);
                return;
        }