linux-kernel - [PATCH tip/core/rcu 2/3] rcu: add debug check for too many rcu_read

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Message-Id: <12626498423064-git-send-email->
Date:	Mon,  4 Jan 2010 16:04:01 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 2/3] rcu: add debug check for too many rcu_read_unlock()

From: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

TREE_PREEMPT_RCU maintains an rcu_read_lock_nesting counter in the
task structure, which happens to be a signed int.  So this patch adds a
check for this counter being negative at the end of __rcu_read_unlock().
This check is under CONFIG_PROVE_LOCKING, so can be thought of as being
part of lockdep.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcutree_plugin.h |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index f11ebd4..e77cdf3 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -304,6 +304,9 @@ void __rcu_read_unlock(void)
 	if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
 	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
 		rcu_read_unlock_special(t);
+#ifdef CONFIG_PROVE_LOCKING
+	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
+#endif /* #ifdef CONFIG_PROVE_LOCKING */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 
-- 
1.5.2.5

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