Re: [PATCH v20 0/7] Virtio-balloon Enhancement

[Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>]

Matthew Wilcox wrote:
> > I think xb_find_set() has a bug in !node path.
> 
> Don't think.  Write a test-case.  Please.  If it shows a bug, then great,

+unsigned long xb_find_set(struct xb *xb, unsigned long size,
+			  unsigned long offset)
+{
+	struct radix_tree_root *root = &xb->xbrt;
+	struct radix_tree_node *node;
+	void __rcu **slot;
+	struct ida_bitmap *bitmap;
+	unsigned long index = offset / IDA_BITMAP_BITS;
+	unsigned long index_end = size / IDA_BITMAP_BITS;
+	unsigned long bit = offset % IDA_BITMAP_BITS;
+
+	if (unlikely(offset >= size))
+		return size;
+
+	while (index <= index_end) {
+		unsigned long ret;
+		unsigned int nbits = size - index * IDA_BITMAP_BITS;
+
+		bitmap = __radix_tree_lookup(root, index, &node, &slot);
+		if (!node) {
+			index = (index | RADIX_TREE_MAP_MASK) + 1;

Why we don't need to reset "bit" to 0 here?
We will continue with wrong offset if "bit != 0", won't we?

+			continue;
+		}
+
+		if (bitmap) {
+			if (nbits > IDA_BITMAP_BITS)
+				nbits = IDA_BITMAP_BITS;
+
+			ret = find_next_bit(bitmap->bitmap, nbits, bit);
+			if (ret != nbits)
+				return ret + index * IDA_BITMAP_BITS;
+		}
+		bit = 0;
+		index++;
+	}
+
+	return size;
+}

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