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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 Jun 2025 13:00:03.9573 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 59355020-6c2d-40b5-712f-08dda29e8ec7 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AMS1EPF00000048.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS2PR08MB8309 On 03/06/25 5:47 pm, Zi Yan wrote: > On 3 Jun 2025, at 3:58, David Hildenbrand wrote: > >> On 03.06.25 07:23, Dev Jain wrote: >>> On 02/06/25 8:33 pm, Zi Yan wrote: >>>> On 29 May 2025, at 23:44, Dev Jain wrote: >>>> >>>>> On 30/05/25 4:17 am, Zi Yan wrote: >>>>>> On 28 May 2025, at 23:17, Dev Jain wrote: >>>>>> >>>>>>> On 28/05/25 10:42 pm, Zi Yan wrote: >>>>>>>> On 28 May 2025, at 7:31, Dev Jain wrote: >>>>>>>> >>>>>>>>> Suppose xas is pointing somewhere near the end of the multi-entry batch. >>>>>>>>> Then it may happen that the computed slot already falls beyond the batch, >>>>>>>>> thus breaking the loop due to !xa_is_sibling(), and computing the wrong >>>>>>>>> order. 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 :) > builds. > > Best Regards, > Yan, Zi