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From: Frederic Weisbecker on 15 Apr 2010 17:20
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, loosing a few hits in a stat is not a big
deal, so increment it without protection.

v2: Don't bother with disabling irq, we can miss one count in
rare situations

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 | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 78325f8..1b58a1b 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -2298,7 +2298,12 @@ void trace_hardirqs_on_caller(unsigned long ip)
return;

if (unlikely(curr->hardirqs_enabled)) {
- debug_atomic_inc(redundant_hardirqs_on);
+ /*
+ * Neither irq nor preemption are disabled here
+ * so this is racy by nature but loosing one hit
+ * in a stat is not a big deal.
+ */
+ this_cpu_inc(lockdep_stats.redundant_hardirqs_on);
return;
}
/* we'll do an OFF -> ON transition: */
--
1.6.2.3

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Prev: [PATCH] Staging: dream: smd: smd_qmi: fix code style issues
Next: [PATCH 2/2] lockdep: Simplify debug atomic ops