[tip:core/urgent] highmem: Fix race in debug_kmap_atomic() which could cause warn_count to underflow

[tip-bot for Soeren Sandmann <sandmann@daimi.au.dk>]

Commit-ID:  5ebd4c22897dce65845807a9bd3a31cc4e142b53
Gitweb:     http://git.kernel.org/tip/5ebd4c22897dce65845807a9bd3a31cc4e142b53
Author:     Soeren Sandmann <sandmann@daimi.au.dk>
AuthorDate: Wed, 28 Oct 2009 18:55:36 +0100
Committer:  Ingo Molnar <mingo@elte.hu>
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 <sandmann@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: a.p.zijlstra@chello.nl
Cc: <stable@kernel.org> # .31.x
LKML-Reference: <ye8zl7b8ktj.fsf@camel23.daimi.au.dk>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 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())) {