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Thus ensure that the caller is aware of this by triggering a BUG >>>>>>>>>>> when the entry is a sibling entry. >>>>>>>>>> Is it possible to add a test case in lib/test_xarray.c for this? >>>>>>>>>> You can compile the tests with “make -C tools/testing/radix-tree” >>>>>>>>>> and run “./tools/testing/radix-tree/xarray”. >>>>>>>>> Sorry forgot to Cc you. >>>>>>>>> I can surely do that later, but does this patch look fine? >>>>>>>> I am not sure the exact situation you are describing, so I asked you >>>>>>>> to write a test case to demonstrate the issue. :) >>>>>>> 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. So I mean to >>>>>>> say that the order computation must start from the beginning of the multi-slot >>>>>>> entries, that is, the non-sibling entry. >>>>>> Got it. Thanks for the explanation. It will be great to add this explanation >>>>>> to the commit log. >>>>>> >>>>>> I also notice that in the comment of xas_get_order() it says >>>>>> “Called after xas_load()” and xas_load() returns NULL or an internal >>>>>> entry for a sibling. So caller is responsible to make sure xas is not pointing >>>>>> to a sibling entry. It is good to have a check here. >>>>>> >>>>>> In terms of the patch, we are moving away from BUG()/BUG_ON(), so I wonder >>>>>> if there is a less disruptive way of handling this. Something like return >>>>>> -EINVAL instead with modified function comments and adding a comment >>>>>> at the return -EIVAL saying something like caller needs to pass >>>>>> a non-sibling entry. >>>>> What's the reason for moving away from BUG_ON()? >>>> BUG_ON is in general a bad thing. See Documentation/process/coding-style.rst and the history on the related changes for details. >>>> >>>> Here, it is less critical than it looks. >>>> >>>> XA_NODE_BUG_ON is only active with XA_DEBUG. >>>> >>>> And XA_DEBUG is only defined in >>>> >>>> tools/testing/shared/xarray-shared.h:#define XA_DEBUG >>>> >>>> So IIUC, it's only active in selftests, and completely inactive in any kernel builds. >>> Oh, I missed that. But that also means this patch becomes a nop in kernel >> Yes, but given other places are there with XA_NODE_BUG_ON(), I believe >> this patch has some value :) > Sure. Can you please also add something like below to the function comment? > “The xas cannot be a sibling entry, otherwise the result will be wrong” > It saves other’s time to infer it from the added XA_NODE_BUG_ON(). Sure. > > Thanks. > > Best Regards, > Yan, Zi