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From: Frederic Weisbecker on 15 Apr 2010 09:40
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(a)canb.auug.org.au>
Signed-off-by: Frederic Weisbecker <fweisbec(a)gmail.com>
Cc: Peter Zijlstra <peterz(a)infradead.org>
Cc: David Miller <davem(a)davemloft.net>
Cc: Benjamin Herrenschmidt <benh(a)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

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