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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1770299083; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=EvavgnhksTGd3tqhlRUGr1n0VgKkunvVmA98Z7pF/Dw=; b=twBrrifThdYBJtC9kqh41TLV788FtCDtetkg6opVdfI24GGDbTR3JQNyT/OxZXUor2iahJ 2nXBpZDM0o4S0ywfDD173Cn29vaIPnsFiFPXHWKeCJl36YxHVpuCapd2jjkKdOSmtyUeIZ Af8mmPMW7NPJKMWvpa9Xx+gqp4QPG3g= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 6D04240BC2; Thu, 5 Feb 2026 13:44:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A732BC4CEF7; Thu, 5 Feb 2026 13:44:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770299082; bh=oN2mtMuaL0wRg06xOfWVYtvkom3Wrc7dRFRV+da+k1M=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=FLxb9xi7xpxwGHRcQ49oia7/YSMbfNHdByXtrqveYFtcJcf18iTZABv4yGzVX5fZD e6hW7jchgeJzSVFqF1/b43yLZhF/bdXuRezcsdIvlyn13/SBa0XHpkzQswqXMDpX+i YDdqIn6C/yYkOufYz4BJEBJqnWVNLLdZrBoO/XgvShsxNnKcau27tDSQ1n/m/tk4l6 jMFzNGHIN1sc9PmcHB+fsKDHm7ZSVOZx7DX0BHp9dBerqyvX6f2E9G9YCNmyijSNi8 vrKEKmV80Em0+uXpwoTwD9kOU/0Wg4JG7wqhsBxfYO9CzxyBRUdUibDUBpdQIuJIy6 oo7fYTYi+PVAA== Message-ID: <90226c5d-4f0a-4a29-8c5f-1b891e724c2b@kernel.org> Date: Thu, 5 Feb 2026 14:44:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [BUG] rcu detected stall in shmem_file_write_iter To: Zw Tang , "linux-mm@kvack.org" , rcu@vger.kernel.org Cc: "hughd@google.com" , "akpm@linux-foundation.org" , chrisl@kernel.org, kasong@tencent.com, paulmck@kernel.org, frederic@kernel.org, "linux-kernel@vger.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; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 764C340014 X-Stat-Signature: misdi886f1by3ar9abu5ujwzh7z7q44r X-HE-Tag: 1770299083-941735 X-HE-Meta: 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 CWWIZWGX u+AxaFcYk1vIAKhTK2QOqSBzs+cPhLOYm6JLvtI1BUVh8Ji5YjfmKnyrXAlCdq9AUvtxwWKukHMjR1XQ6zWofIg9KRWa7MJpEfAu/m+uXAXejbCE4qJ9BS5dILqW7X1ZezFHTweRx8ngtaF5Hanl1BroMgGCqyttalbtvpaUmc46OB7MWRLGJLE6FjXWPE/kRRxBT3XOHQVbnKEykM16nSpakBy948BToiUshWG31MhN1hCPJjr8FgHtqlmPa19106iV4GbYeIdZm6RFerV7E3OJvQMke9RZGAPveoMn+1bkP428DUerHvPl42ZExF4mVfPTZu5TSSPdC7bh2871+jlayiq4Xi8X7xfBO X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/5/26 13:57, Zw Tang wrote: > Hi, > > I am reporting a reproducible RCU stall observed on Linux 6.19.0-rc7, > triggered by a syzkaller C reproducer. > > The stall is reported while a userspace task is executing the tmpfs > (shmem) write path. The blocked task is a syz-executor process, and the > RCU report consistently shows it running in the shmem write / folio > allocation path for an extended period of time. > > The relevant call trace of the stalled task is: > > shmem_file_write_iter > shmem_write_begin > shmem_get_folio_gfp > __folio_batch_add_and_move > folio_batch_move_lru > lru_add > __mod_zone_page_state > lru_add()->lruvec_add_folio() calls update_lru_size()->__update_lru_size()->__mod_zone_page_state(). On SMP systems we end up in mm/vmstat.c:__mod_zone_page_state(). I don't see anything that could block in there. Livelocking? Or we're actually stuck somewhere else and the __mod_zone_page_state is misleading. Can you try running with lockdep to see if anything pops up? -- Cheers, David