linux-kernel - [PATCH v2] mm: BUG when __kmap_atomic_idx equals KM_TYPE

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Message-Id: <1406787871-2951-1-git-send-email-cpandya@codeaurora.org>
Date:	Thu, 31 Jul 2014 11:54:31 +0530
From:	Chintan Pandya <cpandya@...eaurora.org>
To:	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Chintan Pandya <cpandya@...eaurora.org>
Subject: [PATCH v2] mm: BUG when __kmap_atomic_idx equals KM_TYPE_NR

__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@...eaurora.org>
---
Changes:

V1 --> V2

	Not touching CONFIG_DEBUG_HIGHMEM.

 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)
 
 #ifdef CONFIG_DEBUG_HIGHMEM
 	WARN_ON_ONCE(in_irq() && !irqs_disabled());
-	BUG_ON(idx > KM_TYPE_NR);
+	BUG_ON(idx >= KM_TYPE_NR);
 #endif
 	return idx;
 }
-- 
Chintan Pandya

QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation

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