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%3Ba=su...

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@vger.kernel.org know about it.

From 21035965f60b0502fc6537b232839389bb4ce664 Mon Sep 17 00:00:00 2001

From: Omar Sandoval osandov@fb.com Date: Mon, 2 Apr 2018 15:58:31 -0700 Subject: bitmap: fix memset optimization on big-endian systems

From: Omar Sandoval osandov@fb.com

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@kernel.org Reported-by: "Erhard F." erhard_f@mailbox.org Cc: Matthew Wilcox mawilcox@microsoft.com Cc: Rasmus Villemoes linux@rasmusvillemoes.dk Cc: Andrew Morton akpm@linux-foundation.org Cc: Arnd Bergmann arnd@arndb.de Signed-off-by: Omar Sandoval osandov@fb.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- 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@fb.com are

queue-4.16/bitmap-fix-memset-optimization-on-big-endian-systems.patch