Re: [PATCH] bitmap: fix memset optimization on big-endian systems

[Omar Sandoval]

On Mon, Apr 02, 2018 at 03:58:31PM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@xxxxxx>
> 
> Commit 2a98dc028f91 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

This should be stable@xxxxxxxxxxxxxxx, of course