The patch titled
Subject: linux/bitmap.h: handle constant zero-size bitmaps correctly
has been added to the -mm tree. Its filename is
linux-bitmaph-handle-constant-zero-size-bitmaps-correctly.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/linux-bitmaph-handle-constant-zero-size-bitmaps-correctly.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/linux-bitmaph-handle-constant-zero-size-bitmaps-correctly.patch
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------------------------------------------------------
From: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Subject: linux/bitmap.h: handle constant zero-size bitmaps correctly
The static inlines in bitmap.h do not handle a compile-time constant
nbits==0 correctly (they dereference the passed src or dst pointers,
despite only 0 words being valid to access). I had the 0-day buildbot
chew on a patch [1] that would cause build failures for such cases without
complaining, suggesting that we don't have any such users currently, at
least for the 70 .config/arch combinations that was built. Should any
turn up, make sure they use the out-of-line versions, which do handle
nbits==0 correctly.
This is of course not the most efficient, but it's much less churn than
teaching all the static inlines an "if (zero_const_nbits())", and since we
don't have any current instances, this doesn't affect existing code at
all.
[1] lkml.kernel.org/r/20180815085539.27485-1-linux@xxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20180818131623.8755-3-linux@xxxxxxxxxxxxxxxxxx
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Cc: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Sudeep Holla <sudeep.holla@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/bitmap.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
--- a/include/linux/bitmap.h~linux-bitmaph-handle-constant-zero-size-bitmaps-correctly
+++ a/include/linux/bitmap.h
@@ -204,8 +204,13 @@ extern int bitmap_print_to_pagebuf(bool
#define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
#define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
+/*
+ * The static inlines below do not handle constant nbits==0 correctly,
+ * so make such users (should any ever turn up) call the out-of-line
+ * versions.
+ */
#define small_const_nbits(nbits) \
- (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG)
+ (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0)
static inline void bitmap_zero(unsigned long *dst, unsigned int nbits)
{
_
Patches currently in -mm which might be from linux@xxxxxxxxxxxxxxxxxx are
lib-bitmapc-remove-wrong-documentation.patch
linux-bitmaph-handle-constant-zero-size-bitmaps-correctly.patch
linux-bitmaph-remove-redundant-uses-of-small_const_nbits.patch
linux-bitmaph-fix-type-of-nbits-in-bitmap_shift_right.patch
linux-bitmaph-relax-comment-on-compile-time-constant-nbits.patch
lib-bitmapc-fix-remaining-space-computation-in-bitmap_print_to_pagebuf.patch
lib-bitmapc-simplify-bitmap_print_to_pagebuf.patch
