[PATCH] lockdep: Fix redundant_hardirqs_on incremented with irqs enabled

[Frederic Weisbecker <fweisbec@gmail.com>]

When a path restore the flags while irqs are already enabled, we
update the per cpu var redundant_hardirqs_on in a racy fashion
and debug_atomic_inc() warns about this situation.

In this particular case, we need to explictly disable the irqs before
updating this stat var in order to update it safely.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: David Miller <davem@davemloft.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
 kernel/lockdep.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 78325f8..65d4336 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -2298,7 +2298,11 @@ void trace_hardirqs_on_caller(unsigned long ip)
 		return;
 
 	if (unlikely(curr->hardirqs_enabled)) {
+		unsigned long flags;
+
+		raw_local_irq_save(flags);
 		debug_atomic_inc(redundant_hardirqs_on);
+		raw_local_irq_restore(flags);
 		return;
 	}
 	/* we'll do an OFF -> ON transition: */
-- 
1.6.2.3