linux-kernel - [PATCH] lockdep: Fix redundant_hardirqs

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Message-Id: <1271338670-4537-1-git-send-regression-fweisbec@gmail.com>
Date:	Thu, 15 Apr 2010 15:37:50 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Peter Zijlstra <peterz@...radead.org>,
	David Miller <davem@...emloft.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: [PATCH] lockdep: Fix redundant_hardirqs_on incremented with irqs enabled

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@...b.auug.org.au>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: David Miller <davem@...emloft.net>
Cc: Benjamin Herrenschmidt <benh@...nel.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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