linux-kernel - [tip:core/rcu] rcu: Add debug check for too many rcu_read

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Date:	Wed, 13 Jan 2010 10:27:58 GMT
From:	"tip-bot for Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	hpa@...or.com, mingo@...hat.com, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:core/rcu] rcu: Add debug check for too many rcu_read_unlock()

Commit-ID:  cba8244a0f1c277b6b1e48ed6504fa434119e24d
Gitweb:     http://git.kernel.org/tip/cba8244a0f1c277b6b1e48ed6504fa434119e24d
Author:     Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
AuthorDate: Mon, 4 Jan 2010 16:04:01 -0800
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Wed, 13 Jan 2010 09:06:06 +0100

rcu: Add debug check for too many rcu_read_unlock()

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>
Cc: laijs@...fujitsu.com
Cc: dipankar@...ibm.com
Cc: mathieu.desnoyers@...ymtl.ca
Cc: josh@...htriplett.org
Cc: dvhltc@...ibm.com
Cc: niv@...ibm.com
Cc: peterz@...radead.org
Cc: rostedt@...dmis.org
Cc: Valdis.Kletnieks@...edu
Cc: dhowells@...hat.com
LKML-Reference: <12626498423064-git-send-email->
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 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);
 
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