linux-kernel - [PATCH 1/2] Fix race in debug_kmap_atomic() which could cause warn

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Date:	28 Oct 2009 18:55:36 +0100
From:	Soeren Sandmann <sandmann@...mi.au.dk>
To:	linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, a.p.zijlstra@...llo.nl
Subject: [PATCH 1/2] Fix race in debug_kmap_atomic() which could cause warn_count to underflow

debug_kmap_atomic() tries to prevent ever printing more than 10
warnings, but it does so by testing whether an unsigned integer is
equal to 0. However, if the warning is caused by a nested IRQ, then
this counter may underflow and the stream of warnings will never end.

Fix that by using a signed integer instead.

Signed-off-by: SÃ¸ren Sandmann Pedersen <sandmann@...hat.com>
---
 mm/highmem.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/highmem.c b/mm/highmem.c
index 25878cc..33587de 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -426,9 +426,9 @@ void __init page_address_init(void)
 
 void debug_kmap_atomic(enum km_type type)
 {
-	static unsigned warn_count = 10;
+	static int warn_count = 10;
 
-	if (unlikely(warn_count == 0))
+	if (unlikely(warn_count < 0))
 		return;
 
 	if (unlikely(in_interrupt())) {
-- 
1.6.5.1

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