[RFC PATCH] lockdep: update lockdep_recursion on graph_lock

[Steven Rostedt]

With the introduction of ftrace, it is possible to recurse into
the lockdep functions via the mcount call. To prevent possible
lockups, updating the lockdep_recursion counter on grabbing the internal
lockdep_lock should prevent deadlocks.

Signed-off-by: Steven Rostedt <srostedt@xxxxxxxxxx>
---
 kernel/lockdep.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-sched-devel.git/kernel/lockdep.c
===================================================================
--- linux-sched-devel.git.orig/kernel/lockdep.c	2008-04-17 11:20:49.000000000 -0400
+++ linux-sched-devel.git/kernel/lockdep.c	2008-04-17 11:36:48.000000000 -0400
@@ -82,6 +82,8 @@ static int graph_lock(void)
 		__raw_spin_unlock(&lockdep_lock);
 		return 0;
 	}
+	/* prevent any recursions within lockdep from causing deadlocks */
+	current->lockdep_recursion++;
 	return 1;
 }

@@ -90,6 +92,7 @@ static inline int graph_unlock(void)
 	if (debug_locks && !__raw_spin_is_locked(&lockdep_lock))
 		return DEBUG_LOCKS_WARN_ON(1);

+	current->lockdep_recursion--;
 	__raw_spin_unlock(&lockdep_lock);
 	return 0;
 }

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