Re: [PATCH v17 1/6] lib/xbitmap: Introduce xbitmap

I'm commenting without understanding the logic.

Wei Wang wrote:

+
+bool xb_preload(gfp_t gfp);
+

Want __must_check annotation, for __radix_tree_preload() is marked
with __must_check annotation. By error failing to check result of
xb_preload() will lead to preemption kept disabled unexpectedly.

+int xb_set_bit(struct xb *xb, unsigned long bit)
+{
+	int err;
+	unsigned long index = bit / IDA_BITMAP_BITS;
+	struct radix_tree_root *root = &xb->xbrt;
+	struct radix_tree_node *node;
+	void **slot;
+	struct ida_bitmap *bitmap;
+	unsigned long ebit;
+
+	bit %= IDA_BITMAP_BITS;
+	ebit = bit + 2;
+
+	err = __radix_tree_create(root, index, 0, &node, &slot);
+	if (err)
+		return err;
+	bitmap = rcu_dereference_raw(*slot);
+	if (radix_tree_exception(bitmap)) {
+		unsigned long tmp = (unsigned long)bitmap;
+
+		if (ebit < BITS_PER_LONG) {
+			tmp |= 1UL << ebit;
+			rcu_assign_pointer(*slot, (void *)tmp);
+			return 0;
+		}
+		bitmap = this_cpu_xchg(ida_bitmap, NULL);
+		if (!bitmap)

Please write locking rules, in order to explain how memory
allocated by __radix_tree_create() will not leak.

+			return -EAGAIN;
+		memset(bitmap, 0, sizeof(*bitmap));
+		bitmap->bitmap[0] = tmp >> RADIX_TREE_EXCEPTIONAL_SHIFT;
+		rcu_assign_pointer(*slot, bitmap);
+	}
+
+	if (!bitmap) {
+		if (ebit < BITS_PER_LONG) {
+			bitmap = (void *)((1UL << ebit) |
+					RADIX_TREE_EXCEPTIONAL_ENTRY);
+			__radix_tree_replace(root, node, slot, bitmap, NULL,
+						NULL);
+			return 0;
+		}
+		bitmap = this_cpu_xchg(ida_bitmap, NULL);
+		if (!bitmap)

Same here.

+			return -EAGAIN;
+		memset(bitmap, 0, sizeof(*bitmap));
+		__radix_tree_replace(root, node, slot, bitmap, NULL, NULL);
+	}
+
+	__set_bit(bit, bitmap->bitmap);
+	return 0;
+}

+void xb_clear_bit(struct xb *xb, unsigned long bit)
+{
+	unsigned long index = bit / IDA_BITMAP_BITS;
+	struct radix_tree_root *root = &xb->xbrt;
+	struct radix_tree_node *node;
+	void **slot;
+	struct ida_bitmap *bitmap;
+	unsigned long ebit;
+
+	bit %= IDA_BITMAP_BITS;
+	ebit = bit + 2;
+
+	bitmap = __radix_tree_lookup(root, index, &node, &slot);
+	if (radix_tree_exception(bitmap)) {
+		unsigned long tmp = (unsigned long)bitmap;
+
+		if (ebit >= BITS_PER_LONG)
+			return;
+		tmp &= ~(1UL << ebit);
+		if (tmp == RADIX_TREE_EXCEPTIONAL_ENTRY)
+			__radix_tree_delete(root, node, slot);
+		else
+			rcu_assign_pointer(*slot, (void *)tmp);
+		return;
+	}
+
+	if (!bitmap)
+		return;
+
+	__clear_bit(bit, bitmap->bitmap);
+	if (bitmap_empty(bitmap->bitmap, IDA_BITMAP_BITS)) {

Please write locking rules, in order to explain how double kfree() and/or
use-after-free can be avoided.

+		kfree(bitmap);
+		__radix_tree_delete(root, node, slot);
+	}
+}

+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);
+
+			if (ebit >= BITS_PER_LONG)
+				continue;
+			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)) {

Same here.

+				kfree(bitmap);
+				__radix_tree_delete(root, node, slot);
+			}
+		}
+	}
+}

+bool xb_test_bit(struct xb *xb, unsigned long bit)
+{
+	unsigned long index = bit / IDA_BITMAP_BITS;
+	const struct radix_tree_root *root = &xb->xbrt;
+	struct ida_bitmap *bitmap = radix_tree_lookup(root, index);
+
+	bit %= IDA_BITMAP_BITS;
+
+	if (!bitmap)
+		return false;
+	if (radix_tree_exception(bitmap)) {
+		bit += RADIX_TREE_EXCEPTIONAL_SHIFT;
+		if (bit > BITS_PER_LONG)

Why not bit >= BITS_PER_LONG here?

+			return false;
+		return (unsigned long)bitmap & (1UL << bit);
+	}
+
+	return test_bit(bit, bitmap->bitmap);
+}