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b=r4Lo8oTEbgWeJsYAt1GfYDbY1fHRB6yuwVGdkZkptWgGED3irgtI/D9Lvv1CfcKNA woOHhlaPFeQhEKnVtJ5SAy33mMhQjb5z27KSkfiKvB98JQO1/5vSVzitvdD32jwLQz 3+fsNZb0ibFUAUeJkrMO1qSa0EoKkkp3FEt2BbN11Uru68j6AX1EAGTkUqya0QEOB8 Jrh3UKvZmFaq8LXFzpieHtPC6luV1d2dFRiNZb7jwEbpwYZV/1JFI6midrr8AeUu9M CFSMYTG8mcESkoqi/ENhkMJRNmuXEFJ/cjZnYVpkS4ZE/7Zd/QKg7i3YdOHAvfjJRq dUjS6inBtqQtg== Message-ID: <7eb61bf4-5483-43e5-a1b0-87a36cd67b9c@kernel.org> Date: Wed, 18 Mar 2026 11:57:24 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [BUG] WARNING in unlink_anon_vmas() To: Jiakai Xu , LKML , linux-mm@kvack.org Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, harry.yoo@oracle.com, jannh@google.com, lorenzo.stoakes@oracle.com, riel@surriel.com, vbabka@kernel.org 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-Stat-Signature: bmeq4y4w9da533mduoprsr4ygf1j8e9m X-Rspam-User: X-Rspamd-Queue-Id: 2795C180006 X-Rspamd-Server: rspam12 X-HE-Tag: 1773831449-285712 X-HE-Meta: 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 shsLDbdI uribxcEF6imWDms+kAKqsoeXUnbZyWLQFCqTNT5z+7O/WrfJGownUjsNexH+WFNyaw2xctlFqBqf9fMIajAHL/yVULJ6wAt85AvNiMXF63x8f5EjiPqcyUBbfkJoHMK3Z3+LxcUD/ZeXE8tLObwGaXVbZTV4efoqopEqYSLG244o1TxTilaf2/QJthqceSA44KFJpzBqvNLkhZM++q6P6lNZscJDxHth1yU5zDzYpSI6x+uAJ4YEGse8UZ+w0EiCSKV2vmdct0Cd1q061erlHhjfN0CoAj5bZLHDKL1MXpv9hCPnDhys5Mq7VgBiPlgTM5APghifPye1PWJqWrnQ4skXGqSgjxHgkifFF4LwvGEBpEvKCWAp4PoBksARiui9hTYq9 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/18/26 11:42, Jiakai Xu wrote: > Hi all, Hi, > > While fuzzing the KVM subsystem on RISC-V, I stumbled upon a kernel WARNING > that triggers in unlink_anon_vmas(). > Looking at the log, this is against 7.0.0-rc2-00014-gc61ec3e8cc5d > WARNING: mm/rmap.c:528 at unlink_anon_vmas+0x562/0x768 mm/rmap.c:528 > unlink_anon_vmas+0x562/0x768 mm/rmap.c:528 > free_pgtables+0x2a0/0x860 mm/memory.c:427 > exit_mmap+0x406/0xd14 mm/mmap.c:1314 > __mmput+0x114/0x3d4 kernel/fork.c:1174 > mmput+0x74/0x88 kernel/fork.c:1197 > exit_mm kernel/exit.c:581 [inline] > do_exit+0x7de/0x2adc kernel/exit.c:959 > do_group_exit+0xd4/0x26c kernel/exit.c:1112 > __do_sys_exit_group kernel/exit.c:1123 [inline] > __se_sys_exit_group kernel/exit.c:1121 [inline] > __riscv_sys_exit_group+0x4a/0x54 kernel/exit.c:1121 > syscall_handler+0x94/0x118 arch/riscv/include/asm/syscall.h:112 > do_trap_ecall_u+0x39e/0x62e arch/riscv/kernel/traps.c:344 > handle_exception+0x15e/0x16a arch/riscv/kernel/entry.S:232 > > I am not an expert in this area and have not done a deep manual analysis. > > The full crash log, a reproducer, the kernel .config, and the relevant > source/commit info are available in my GitHub repository: > https://github.com/j1akai/temp/tree/main/20260318 > > If this turns out to be a real bug and there is anything I can do to help > with fixing or testing, I am happy to do so. I hope this report is useful > and sorry for any noise if it has already been addressed. We trigger a VM_WARN_ON, so that's certainly something to resolve. Seems to be: VM_WARN_ON(anon_vma->num_active_vmas); Which was added by commit 2555283eb40df89945557273121e9393ef9b542b Author: Jann Horn Date: Wed Aug 31 19:06:00 2022 +0200 mm/rmap: Fix anon_vma->degree ambiguity leading to double-reuse anon_vma->degree tracks the combined number of child anon_vmas and VMAs that use the anon_vma as their ->anon_vma. -- Cheers, David