Wei Wang wrote:
> /**
> + * xb_clear_bit - clear a range of bits in the xbitmap
Name mismatch.
> + * @start: the start of the bit range, inclusive
> + * @end: the end of the bit range, inclusive
> + *
> + * This function is used to clear a bit in the xbitmap. If all the bits of the
> + * bitmap are 0, the bitmap will be freed.
> + */
> +void xb_clear_bit_range(struct xb *xb, unsigned long start, unsigned long end)
> +{
> + struct radix_tree_root *root = &xb->xbrt;
> + struct radix_tree_node *node;
> + void **slot;
> + struct ida_bitmap *bitmap;
> + unsigned int nbits;
> +
> + for (; start < end; start = (start | (IDA_BITMAP_BITS - 1)) + 1) {
> + unsigned long index = start / IDA_BITMAP_BITS;
> + unsigned long bit = start % IDA_BITMAP_BITS;
> +
> + bitmap = __radix_tree_lookup(root, index, &node, &slot);
> + if (radix_tree_exception(bitmap)) {
> + unsigned long ebit = bit + 2;
> + unsigned long tmp = (unsigned long)bitmap;
> +
> + nbits = min(end - start + 1, BITS_PER_LONG - ebit);
"nbits = min(end - start + 1," seems to expect that start == end is legal
for clearing only 1 bit. But this function is no-op if start == end.
Please clarify what "inclusive" intended.
> +
> + if (ebit >= BITS_PER_LONG)
> + continue;
(I don't understand how radix tree works, but generally this patchset looks fuzzy
to me about boundary cases. Thus, I want to confirm that this is not an overlook.)
Why is making "ebit >= BITS_PER_LONG" (e.g. start == 62) case a no-op correct?
Aren't there bits which should have been cleared in this case?
> + bitmap_clear(&tmp, ebit, nbits);
> + if (tmp == RADIX_TREE_EXCEPTIONAL_ENTRY)
> + __radix_tree_delete(root, node, slot);
> + else
> + rcu_assign_pointer(*slot, (void *)tmp);
> + } else if (bitmap) {
> + nbits = min(end - start + 1, IDA_BITMAP_BITS - bit);
> +
> + if (nbits != IDA_BITMAP_BITS)
> + bitmap_clear(bitmap->bitmap, bit, nbits);
> +
> + if (nbits == IDA_BITMAP_BITS ||
> + bitmap_empty(bitmap->bitmap, IDA_BITMAP_BITS)) {
> + kfree(bitmap);
> + __radix_tree_delete(root, node, slot);
> + }
> + }
> + }
> +}
> +static inline __always_inline void bitmap_clear(unsigned long *map,
> + unsigned int start,
> + unsigned int nbits)
> +{
> + 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))
It looks strange to apply __builtin_constant_p test to variables after "& 7".
> + memset((char *)map + start / 8, 0, nbits / 8);
> + else
> + __bitmap_clear(map, start, nbits);
> +}
> +
