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Date:	Tue, 10 Nov 2009 03:19:28 GMT
From:	tip-bot for Soeren Sandmann <>
Subject: [tip:core/urgent] highmem: Fix race in debug_kmap_atomic() which could cause warn_count to underflow

Commit-ID:  5ebd4c22897dce65845807a9bd3a31cc4e142b53
Author:     Soeren Sandmann <>
AuthorDate: Wed, 28 Oct 2009 18:55:36 +0100
Committer:  Ingo Molnar <>
CommitDate: Tue, 10 Nov 2009 04:15:32 +0100

highmem: 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: Soeren Sandmann Pedersen <>
Cc: Linus Torvalds <>
Cc: <> # .31.x
LKML-Reference: <>
Signed-off-by: Ingo Molnar <>
 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))
 	if (unlikely(in_interrupt())) {
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