[PATCH v2] mm: BUG when __kmap_atomic_idx equals KM_TYPE_NR

From: Chintan Pandya
Date: Thu Jul 31 2014 - 02:24:47 EST

__kmap_atomic_idx is per_cpu variable. Each CPU can
use KM_TYPE_NR entries from FIXMAP i.e. from 0 to
KM_TYPE_NR - 1. Allowing __kmap_atomic_idx to over-
shoot to KM_TYPE_NR can mess up with next CPU's 0th
entry which is a bug. Hence BUG_ON if
__kmap_atomic_idx >= KM_TYPE_NR.

Signed-off-by: Chintan Pandya <cpandya@xxxxxxxxxxxxxx>

V1 --> V2


include/linux/highmem.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 7fb31da..9286a46 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -93,7 +93,7 @@ static inline int kmap_atomic_idx_push(void)

WARN_ON_ONCE(in_irq() && !irqs_disabled());
- BUG_ON(idx > KM_TYPE_NR);
+ BUG_ON(idx >= KM_TYPE_NR);
return idx;
Chintan Pandya

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