This is a note to let you know that I've just added the patch titled
bitmap: fix memset optimization on big-endian systems
to the 4.16-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bitmap-fix-memset-optimization-on-big-endian-systems.patch
and it can be found in the queue-4.16 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 21035965f60b0502fc6537b232839389bb4ce664 Mon Sep 17 00:00:00 2001
From: Omar Sandoval <osandov@xxxxxx>
Date: Mon, 2 Apr 2018 15:58:31 -0700
Subject: bitmap: fix memset optimization on big-endian systems
From: Omar Sandoval <osandov@xxxxxx>
commit 21035965f60b0502fc6537b232839389bb4ce664 upstream.
Commit 2a98dc028f91 ("include/linux/bitmap.h: turn bitmap_set and
bitmap_clear into memset when possible") introduced an optimization to
bitmap_{set,clear}() which uses memset() when the start and length are
constants aligned to a byte.
This is wrong on big-endian systems; our bitmaps are arrays of unsigned
long, so bit n is not at byte n / 8 in memory. This was caught by the
Btrfs selftests, but the bitmap selftests also fail when run on a
big-endian machine.
We can still use memset if the start and length are aligned to an
unsigned long, so do that on big-endian. The same problem applies to
the memcmp in bitmap_equal(), so fix it there, too.
Fixes: 2a98dc028f91 ("include/linux/bitmap.h: turn bitmap_set and bitmap_clear into memset when possible")
Fixes: 2c6deb01525a ("bitmap: use memcmp optimisation in more situations")
Cc: stable@xxxxxxxxxx
Reported-by: "Erhard F." <erhard_f@xxxxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/bitmap.h | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -302,12 +302,20 @@ static inline void bitmap_complement(uns
__bitmap_complement(dst, src, nbits);
}
+#ifdef __LITTLE_ENDIAN
+#define BITMAP_MEM_ALIGNMENT 8
+#else
+#define BITMAP_MEM_ALIGNMENT (8 * sizeof(unsigned long))
+#endif
+#define BITMAP_MEM_MASK (BITMAP_MEM_ALIGNMENT - 1)
+
static inline int bitmap_equal(const unsigned long *src1,
const unsigned long *src2, unsigned int nbits)
{
if (small_const_nbits(nbits))
return !((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits));
- if (__builtin_constant_p(nbits & 7) && IS_ALIGNED(nbits, 8))
+ if (__builtin_constant_p(nbits & BITMAP_MEM_MASK) &&
+ IS_ALIGNED(nbits, BITMAP_MEM_ALIGNMENT))
return !memcmp(src1, src2, nbits / 8);
return __bitmap_equal(src1, src2, nbits);
}
@@ -358,8 +366,10 @@ static __always_inline void bitmap_set(u
{
if (__builtin_constant_p(nbits) && nbits == 1)
__set_bit(start, map);
- else if (__builtin_constant_p(start & 7) && IS_ALIGNED(start, 8) &&
- __builtin_constant_p(nbits & 7) && IS_ALIGNED(nbits, 8))
+ else if (__builtin_constant_p(start & BITMAP_MEM_MASK) &&
+ IS_ALIGNED(start, BITMAP_MEM_ALIGNMENT) &&
+ __builtin_constant_p(nbits & BITMAP_MEM_MASK) &&
+ IS_ALIGNED(nbits, BITMAP_MEM_ALIGNMENT))
memset((char *)map + start / 8, 0xff, nbits / 8);
else
__bitmap_set(map, start, nbits);
@@ -370,8 +380,10 @@ static __always_inline void bitmap_clear
{
if (__builtin_constant_p(nbits) && nbits == 1)
__clear_bit(start, map);
- else if (__builtin_constant_p(start & 7) && IS_ALIGNED(start, 8) &&
- __builtin_constant_p(nbits & 7) && IS_ALIGNED(nbits, 8))
+ else if (__builtin_constant_p(start & BITMAP_MEM_MASK) &&
+ IS_ALIGNED(start, BITMAP_MEM_ALIGNMENT) &&
+ __builtin_constant_p(nbits & BITMAP_MEM_MASK) &&
+ IS_ALIGNED(nbits, BITMAP_MEM_ALIGNMENT))
memset((char *)map + start / 8, 0, nbits / 8);
else
__bitmap_clear(map, start, nbits);
Patches currently in stable-queue which might be from osandov@xxxxxx are
queue-4.16/bitmap-fix-memset-optimization-on-big-endian-systems.patch