linux-kernel - [PATCH v1 4/4] bitmap: Make bitmap_fill() and bitmap

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Date:   Tue,  9 Jan 2018 19:24:30 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Randy Dunlap <rdunlap@...radead.org>,
        Yury Norov <ynorov@...iumnetworks.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: [PATCH v1 4/4] bitmap: Make bitmap_fill() and bitmap_zero() consistent

Behaviour of bitmap_fill() differs from bitmap_zero() in a way
how bits behind bitmap are handed. bitmap_zero() clears entire bitmap
by unsigned long boundary, while bitmap_fill() mimics bitmap_set().

Here we change bitmap_fill() behaviour to be consistent with bitmap_zero()
and add a note to documentation.

The change might reveal some bugs in the code where unused bits handled
differently and in such cases bitmap_set() has to be used.

Suggested-by: Rasmus Villemoes <linux@...musvillemoes.dk>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
 include/linux/bitmap.h | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index a17b5121d4f5..49aea0b37994 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -67,6 +67,11 @@
  *  bitmap_from_arr32(dst, buf, nbits)          Copy nbits from u32[] buf to dst
  *  bitmap_to_arr32(buf, src, nbits)            Copy nbits from buf to u32[] dst
  *
+ * Note, bitmap_zero() and bitmap_fill() operate over the region of
+ * unsigned longs, that is, bits behind bitmap till the unsigned long
+ * boundary will be zeroed or filled as well. Consider to use
+ * bitmap_clear() or bitmap_set() to make explicit zeroing or filling
+ * respectively.
  */
 
 /**
@@ -206,12 +211,12 @@ static inline void bitmap_zero(unsigned long *dst, unsigned int nbits)
 
 static inline void bitmap_fill(unsigned long *dst, unsigned int nbits)
 {
-	unsigned int nlongs = BITS_TO_LONGS(nbits);
-	if (!small_const_nbits(nbits)) {
-		unsigned int len = (nlongs - 1) * sizeof(unsigned long);
-		memset(dst, 0xff,  len);
+	if (small_const_nbits(nbits))
+		*dst = ~0UL;
+	else {
+		unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
+		memset(dst, 0xff, len);
 	}
-	dst[nlongs - 1] = BITMAP_LAST_WORD_MASK(nbits);
 }
 
 static inline void bitmap_copy(unsigned long *dst, const unsigned long *src,
-- 
2.15.1