linux-kernel - [PATCH] linux/bitmap.h: fix BITMAP_LAST_WORD

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Date:   Thu, 26 Jul 2018 16:07:51 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        ynorov@...iumnetworks.com, corbet@....net, linux@...musvillemoes.dk
Cc:     dgilbert@...hat.com, mawilcox@...rosoft.com, wei.w.wang@...el.com
Subject: [PATCH] linux/bitmap.h: fix BITMAP_LAST_WORD_MASK

The existing BITMAP_LAST_WORD_MASK macro returns 0xffffffff if nbits is
0. This patch changes the macro to return 0 when there is no bit needs to
be masked.

Signed-off-by: Wei Wang <wei.w.wang@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Yury Norov <ynorov@...iumnetworks.com>
---
 include/linux/bitmap.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 1ee46f4..12af3d7 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -194,7 +194,10 @@ extern int bitmap_print_to_pagebuf(bool list, char *buf,
 				   const unsigned long *maskp, int nmaskbits);
 
 #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
-#define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
+#define BITMAP_LAST_WORD_MASK(nbits)				\
+(								\
+	nbits ? (~0UL >> (-(nbits) & (BITS_PER_LONG - 1))) : 0	\
+)
 
 #define small_const_nbits(nbits) \
 	(__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG)
-- 
2.7.4