Hang on, don't tell me you found this by inspection. Are you not running the bitmap testcase, enabled by CONFIG_TEST_BITMAP? Either that should be producing an error, or there's a missing test case, or your inspection is wrong ... > -----Original Message----- > From: Paul Mackerras [mailto:paulus@xxxxxxxxxx] > Sent: Wednesday, October 25, 2017 2:57 AM > To: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>; Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx>; lkml@xxxxxxxxxxxxxxx > Cc: linuxppc-dev@xxxxxxxxxx; linux-s390@xxxxxxxxxxxxxxx > Subject: [PATCH] bitmap: Fix optimization of bitmap_set/clear for big-endian > machines > > Commit 2a98dc028f91 ("include/linux/bitmap.h: turn bitmap_set and > bitmap_clear into memset when possible", 2017-07-10) added an > optimization which effectively assumes that a contiguous set of > bits in a bitmap will be stored in a contiguous set of bytes of > the bitmap, in the case where the starting bit number and number of > bits are multiples of 8. This is true for a little-endian > representation, but not for a big-endian representation, because we > number the bits of a long from right to left for both little-endian > and big-endian representations. > > The optimization can still be done for big-endian platforms, but > only if the starting bit number and number of bits are multiples > of BITS_PER_LONG. This adjusts the code to use 8 for little-endian > and BITS_PER_LONG for big-endian platforms. > > Cc: stable@xxxxxxxxxxxxxxx # v4.13 > Fixes: 2a98dc028f91 ("include/linux/bitmap.h: turn bitmap_set and > bitmap_clear into memset when possible") > Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx> > --- > This was found by inspection. > > I'm pretty sure commit 2c6deb01525a is wrong as well on big-endian > machines. > > include/linux/bitmap.h | 14 ++++++++++---- > 1 file changed, 10 insertions(+), 4 deletions(-) > > diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h > index 700cf5f..44e2eb4 100644 > --- a/include/linux/bitmap.h > +++ b/include/linux/bitmap.h > @@ -174,8 +174,10 @@ extern unsigned int bitmap_to_u32array(u32 *buf, > unsigned int nbits); > #ifdef __BIG_ENDIAN > extern void bitmap_copy_le(unsigned long *dst, const unsigned long *src, > unsigned int nbits); > +#define BITMAP_MIN_UNIT BITS_PER_LONG /* have to access as > longs */ > #else > #define bitmap_copy_le bitmap_copy > +#define BITMAP_MIN_UNIT 8 /* can access as bytes if > desired */ > #endif > extern unsigned int bitmap_ord_to_pos(const unsigned long *bitmap, > unsigned int ord, unsigned int nbits); > extern int bitmap_print_to_pagebuf(bool list, char *buf, > @@ -317,8 +319,10 @@ static __always_inline void bitmap_set(unsigned long > *map, unsigned int start, > { > 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_MIN_UNIT-1)) && > + IS_ALIGNED(start, BITMAP_MIN_UNIT) && > + __builtin_constant_p(nbits & (BITMAP_MIN_UNIT-1)) && > + IS_ALIGNED(nbits, BITMAP_MIN_UNIT)) > memset((char *)map + start / 8, 0xff, nbits / 8); > else > __bitmap_set(map, start, nbits); > @@ -329,8 +333,10 @@ static __always_inline void bitmap_clear(unsigned > long *map, unsigned int start, > { > 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_MIN_UNIT-1)) && > + IS_ALIGNED(start, BITMAP_MIN_UNIT) && > + __builtin_constant_p(nbits & (BITMAP_MIN_UNIT-1)) && > + IS_ALIGNED(nbits, BITMAP_MIN_UNIT)) > memset((char *)map + start / 8, 0, nbits / 8); > else > __bitmap_clear(map, start, nbits); > -- > 2.7.4 ��.n��������+%������w��{.n�����{��������ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
