[PATCH RFC tip/core/rcu 13/18] rcu: add debug check for too many rcu_read_unlock()

[Paul E. McKenney]

From: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

Proposed for 2.6.34, not for inclusion.

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@xxxxxxxxxxxxxxxxxx>
---
 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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