[021/119] highmem: Fix race in debug_kmap_atomic() which could cause warn_count to underflow

[Greg KH]

2.6.31-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Soeren Sandmann <sandmann@xxxxxxxxxxx>

commit 5ebd4c22897dce65845807a9bd3a31cc4e142b53 upstream.

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: Soeren Sandmann Pedersen <sandmann@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: a.p.zijlstra@xxxxxxxxx
LKML-Reference: <ye8zl7b8ktj.fsf@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 mm/highmem.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- 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())) {


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