rcu: Remove local_irq_disable() in rcu_preempt_note_context_switch()
The rcu_preempt_note_context_switch() function is on a scheduling fast
path, so it would be good to avoid disabling irqs. The reason that irqs
are disabled is to synchronize process-level and irq-handler access to
the task_struct ->rcu_read_unlock_special bitmask. This commit therefore
makes ->rcu_read_unlock_special instead be a union of bools with a short
allowing single-access checks in RCU's __rcu_read_unlock(). This results
in the process-level and irq-handler accesses being simple loads and
stores, so that irqs need no longer be disabled. This commit therefore
removes the irq disabling from rcu_preempt_note_context_switch().
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 03b2748..77fc43f 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -111,7 +111,7 @@
#ifdef CONFIG_PREEMPT_RCU
#define INIT_TASK_RCU_PREEMPT(tsk) \
.rcu_read_lock_nesting = 0, \
- .rcu_read_unlock_special = 0, \
+ .rcu_read_unlock_special.s = 0, \
.rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry), \
INIT_TASK_RCU_TREE_PREEMPT()
#else