linux-kernel - [PATCH 4/8] rcu: delay task rcu state cleanup in exit

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Date:	Wed, 7 Aug 2013 18:25:00 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	Dipankar Sarma <dipankar@...ibm.com>
Subject: [PATCH 4/8] rcu: delay task rcu state cleanup in exit_rcu()

exit_rcu() tries to clean up the task rcu state when the task is exiting.
It did it by calls __rcu_read_unlock().

Actually, calling rcu_read_unlock_special() is enough. This patch defer it
to the rcu_preempt_note_context_switch() of the next schedule().

This patch prepares for the next patch which defers rcu_read_unlock_special()
if irq is disabled when __rcu_read_unlock() is called.
So __rcu_read_unlock() can't work here(it is irq-disabled here)
if the next patch applied.

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
 kernel/rcutree_plugin.h |   11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 6b23b6f..fc8b36f 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -942,10 +942,13 @@ void exit_rcu(void)
 
 	if (likely(list_empty(&current->rcu_node_entry)))
 		return;
-	t->rcu_read_lock_nesting = 1;
-	barrier();
-	t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
-	__rcu_read_unlock();
+	WARN_ON_ONCE(!(t->rcu_read_unlock_special | RCU_READ_UNLOCK_BLOCKED));
+	/*
+	 * Task RCU state(rcu_node_entry) of this task will be cleanup by
+	 * the next rcu_preempt_note_context_switch() of the next schedule()
+	 * in the do_exit().
+	 */
+	t->rcu_read_lock_nesting = INT_MIN;
 }
 
 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
-- 
1.7.4.4

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