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For example, suppose we have a shift-6 node having an order-9 >> entry => 8 - 1 = 7 siblings, so assume the slots are at offset 0 till 7 in >> this node. If xas->xa_offset is 6, then the code will compute order as >> 1 + xas->xa_node->shift = 7. Therefore, the order computation must start >> from the beginning of the multi-slot entries, that is, the non-sibling >> entry. Thus ensure that the caller is aware of this by triggering a BUG >> when the entry is a sibling entry. > Why check this thing in particular? There are a zillion things we > could check... Well, it jumped out to me while reading code. If the concensus is that a BUG_ON() is totally unnecessary, I will at least prefer a comment. I just thought that there are XA_NODE_BUG_ON()'s all over the place, and they must be there for some good reason, so let's follow that. >> Note that this BUG_ON() is only >> active while running selftests, so there is no overhead in a running >> kernel. > hm, how do we know this? Now and in the future? xa_get_order() and > xas_get_order() have callers all over the place. XA_NODE_BUG_ON() depends on #ifdef XA_DEBUG(), which is defined in a tools/testing directory...and in the future if this changes then I think that work will include removing all XA_NODE_BUG_ON()'s... >