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b=gd49k6HM86HJOavNiYPbzwo4gVsgs2BU12luvHrMFjjNLPoEdN4VrwtaGEvbYPNNS mY7JgPf8AleDXMyDWW7MZmU9dNtY1LrQ96+gACmj1foWn+Ilo/qHNT+UNO0w27AN1i d+pJ1x7r1tmFsVBYGDDU6nBC83htBoG5zpsK3vU349J2SYn56M6puR8VXu0hUY0wLu cVoF91ZyTJEaBuibZr48VTVBjX5HD+bd8ttJb+1B5lEcXXNQKISLPAi3hkmzXba9wK vNMbB5hKG+Rt5vtBXhQKYlYYdkVfebwPXWkLTrE8Y9v3s4a/k7E5EI51OcPxnOFfLG jAtePRbYx+ilw== Message-ID: <6ada27e1-8f85-4b85-8c25-bc9207b2624d@kernel.org> Date: Mon, 16 Mar 2026 17:23:17 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v3 0/2] Fix storing in XArray check_split tests To: Ackerley Tng , willy@infradead.org, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: michael.roth@amd.com, dev.jain@arm.com, vannapurve@google.com, Zi Yan References: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 8885FA0002 X-Stat-Signature: 57qwgdz1iqwd8unc78o5ikp37xshroxk X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1773678202-31590 X-HE-Meta: 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 1NQN1pzQ 50fde3/kaN9RiBVv1LWh25g5/Tstle93dZcTHxAq9rkknqKOgNbipPKmEdJSMPxxflXsCNoetoDoMyq8zdB1AuoKAZA/0pKH6D2FIIIzWo+Cw0QhTli3oxsBmwwlEnSVd9EJs9il+0FSXU3JpUlo2TRpsIpOfA59Y5XmoLOC9Va2uWwcuqkivd6/VKP2bCrSNSsIHVnCZNcC+hcRKSuCB5snz+MxXRHwVqFWBgs9R6oVlACRFDlt0ZBtdTwjzB8ZcUTMwVey+7mwmKQhsKDGzAj9+LJl3rcP5lasP9e4pPzjbS/6Sm8s6iBGhyQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/23/26 08:34, Ackerley Tng wrote: > Hi, > > I hit an assertion while making some modifications to > lib/test_xarray.c [1] and I believe this is the fix. > > In check_split, the tests split the XArray node and then store values > after the split to verify that splitting worked. While storing and > retrieval works as expected, the node's metadata, specifically > node->nr_values, is not updated correctly. > > This led to the assertion being hit in [1], since the storing process > did not increment node->nr_values sufficiently, while the erasing > process assumed the fully-incremented node->nr_values state. > > Would like to check my understanding on these: > > 1. In the multi-index xarray world, is node->nr_values definitely the > total number of values *and siblings* in the node? > > 2. IIUC xas_store() has significantly different behavior when entry is > NULL vs non-NULL: when entry is NULL, xas_store() does not make > assumptions on the number of siblings and erases all the way till > the next non-sibling entry. This sounds fair to me, but it's also > kind of surprising that it is differently handled when entry is > non-NULL, where xas_store() respects xas->xa_sibs. > > 3. If xas_store() is dependent on its caller to set up xas correctly > (also sounds fair), then there are places where xas_store() is > used, like replace_page_cache_folio() or > migrate_huge_page_move_mapping(), where xas is set up assuming 0 > order pages. Are those buggy? Zi, do you have any familiarity with that code and could help? Thanks! -- Cheers, David