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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 Jun 2025 05:24:10.9044 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 6311143f-dd3b-4b44-9939-08dda25edf18 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: DU6PEPF0000B61F.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DBBPR08MB10555 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()? I would think that it is better that we don't have any overhead without the relevant debug config. Also, returning any negative return value seems more disruptive :) we will have to change all the callers to handle that, and in turn, handle that for their callers, and so on. > > Best Regards, > Yan, Zi