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>

1 files changed, 1 insertions, 1 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 03b274873b06..77fc43f8fb72 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -111,7 +111,7 @@ extern struct group_info init_groups;
 #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