include/linux/bitmap.h: make bitmap_fill() and bitmap_zero() consistent

Web:        https://git.kernel.org/torvalds/c/334cfa48d38f5416c125a71a57f72d6cf634d797
Commit:     334cfa48d38f5416c125a71a57f72d6cf634d797
Parent:     fe81814c3e091adde489e9d7ac1179340845e396
Refname:    refs/heads/master
Author:     Andy Shevchenko <[email protected]>
AuthorDate: Tue Feb 6 15:38:20 2018 -0800
Committer:  Linus Torvalds <[email protected]>
CommitDate: Tue Feb 6 18:32:44 2018 -0800

    include/linux/bitmap.h: 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 are
    handled differently and in such cases bitmap_set() has to be used.
    
    Link: http://lkml.kernel.org/r/[email protected]
    Signed-off-by: Andy Shevchenko <[email protected]>
    Suggested-by: Rasmus Villemoes <[email protected]>
    Cc: Randy Dunlap <[email protected]>
    Cc: Yury Norov <[email protected]>
    Signed-off-by: Andrew Morton <[email protected]>
    Signed-off-by: Linus Torvalds <[email protected]>
---
 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 e43533ec7660..d9bf699e0e7a 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.
  */
 
 /**
@@ -202,12 +207,12 @@ 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,
--
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