Lachlan McIlroy wrote:
> final is calculated to be the last bit to set (ie inclusive) but when we
> do the mask shifting final really needs to be first bit not to set.
>
> For example if first and final are both bit 0 (ie only first bit to be set)
> then mask is completely shifted and becomes all zeroes.
>
> Or if first is 0 and final is 63 then the mask is shifted one bit when it
> shouldn't be shifted at all.
Lachlan, what's the end result of this bug? What's the broken behavior?
Thanks,
-Eric
> --- xfs-fix.orig/fs/xfs/linux-2.6/xfs_buf.c
> +++ xfs-fix/fs/xfs/linux-2.6/xfs_buf.c
> @@ -129,15 +129,17 @@ page_region_mask(
> int first, final;
>
> first = BTOPR(offset);
> - final = BTOPRT(offset + length - 1);
> - first = min(first, final);
> + final = BTOPRT(offset + length);
> +
> + if (first >= final)
> + return 0UL;
>
> mask = ~0UL;
> mask <<= BITS_PER_LONG - (final - first);
> mask >>= BITS_PER_LONG - (final);
>
> ASSERT(offset + length <= PAGE_CACHE_SIZE);
> - ASSERT((final - first) < BITS_PER_LONG && (final - first) >= 0);
> + ASSERT((final - first) <= BITS_PER_LONG && (final - first) > 0);
>
> return mask;
> }
>
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