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imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=OAYiie9x; spf=pass (imf03.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1775042585; a=rsa-sha256; cv=none; b=RklJwpn9m7REkiYaWdTMJn7UXjqMGsb6mPnZZoJAqQaNURNRgOVeiCtXXMwqm2vg5DgTur I4k76oh1+uiICeoXQvBis15ut/RNlXqY4zjLlQRCUclxfzoeHILUqW8tKUNUF7De/i4bpj pBaWwl157X8jtrk1n+s4culbj3VI6t4= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id A6DC5408CA; Wed, 1 Apr 2026 11:23:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DBA60C4CEF7; Wed, 1 Apr 2026 11:23:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775042584; bh=J0EmuxBv/Kz9NWrvoGinSM8UV0p+xOj5OhofK5if/u8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=OAYiie9xMgfT6uDxgfp0lBvoMUkXBKZEv9Ad+PONHhE3osiVap6EDg7S83N6dOxG4 BOhBKX9EW+wWtspp3GHKQuJPhXcHMrHwSiOen7j+dXdYfQoLg+HvR+Rlut+b4Vs8Y9 hiHL0/gZ1FGKpgzoDI84Zt103PIGfijevKrRKZSnaoN/8zLX978yPK3Zt6nJ6mIjFH SitOr1lq0lBz/bhpbeYlZJ6XyfWqbAlu4zC2eWxfL5grIzkHHS9Y0GWFOl3ZXCacq0 yHrBkUWwSILHjsbB0dxQqzMEYIc6D57gX7vk1/uEhLHkYkPJEHILGqeeA8RyWUX6cl gjPALjSfzUSzg== Message-ID: <38a347dc-8a1c-4d04-926d-7a6318e93ca2@kernel.org> Date: Wed, 1 Apr 2026 13:22:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [mm?] WARNING in deferred_split_folio To: Lance Yang Cc: kartikey406@gmail.com, usama.arif@linux.dev, Liam.Howlett@oracle.com, ziy@nvidia.com, syzbot+a7067a757858ac8eb085@syzkaller.appspotmail.com, akpm@linux-foundation.org, baohua@kernel.org, baolin.wang@linux.alibaba.com, dev.jain@arm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, npache@redhat.com, ryan.roberts@arm.com, syzkaller-bugs@googlegroups.com References: <20260401112049.18634-1-lance.yang@linux.dev> 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: <20260401112049.18634-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 92A2F20005 X-Stat-Signature: iuw4ffqi8z31znp64w7jq57xr5z5fjw6 X-Rspamd-Server: rspam06 X-HE-Tag: 1775042585-553396 X-HE-Meta: U2FsdGVkX1+3AhuMIqsVZlDweVsdBeO5kjPEi+ptpD6HI1t2v60zkmljElmZ5Lo7+saDSFdK5NhkG2NtifPscfQiAt4JacWogCF/fnH9ezBkgeZR5ZV/Loasoh7wsMxusfLA8iQt+4eqzDFgCQD3pykMyy7wJI/RQUfjvjv8Td5lTUOm4lVT6eFJ+mD0qk5M72Cn3U7F3FigyO4C1kFXXOOaP4BvPthnJ2rUdQPvPf8YxehLY1RBcqC+WqLm/jjjGEh/ZY0W8BDDKE2D6WILvqeyKNdXij3n/Cw0QFgv1LoAzagBrbTWb1tXfeUEyXlhh5+b6FVj8Z4fKfrQhik0/ksI6uV/SyoFPcUzXdpuOhouX8mR6hmFumOumVHrSY5VeA3knrLlvxPz77hVLfaj6kMUCCY3KWp3q9y/ofOQuNAoEO8UNmjCRidOzIQHBorkt/lOhFKA/IS7gTFXH09UJ32t4LBgXPv4HrOIlcaOQSgU0kjwFMfVTo9EnDVfjrujdwKDr0JT/G9z00LI+q3z+fP3elRmX9FXoyAQ8MClQj2XKC5xae6FCl0RNH5fKosFv+FDonAcmwdyRCxdLJOuzRxBik/7oSoYmpGqHgMX7bP5k+yEle3YUeP+b55bvHflc2ko5zwrWjVSME3O8HM+Um3N8J0dAL+Gc+36M8g55OcFhU3x/xj/Swc5S34GloE3MG5dOrQZxQ4wK+JSLmQ2n6TwSiw+hO5dvbhe5hLS+tdrqXwyXiMs4nrrBaHVPUS0A+PCo0JxWFpvEI/VrWLH/55IThlZDclOXLYRpsrWApyleqjTmC/UIY3e+ktUpZfa7MrWF4/RGrmPnrUpXDa5bonouGB5JW0lS6sgMDyjHTKLFiqmdbN1eGm6DJ86BgkeHo9HUON+1qYpxM4huOEegB4LWLsRZ4pFYp16FQvbkRSkUaLo2yF5HYdWyTjUAtyWU2/cTatSQ4oJmuRYgPB riiOkOGN X0o9qKcwsfTYU3o0PksQSpg21vvsFHrq9ACmqhG4IU3/KKR8E/fbUai9oTiFMdxSmHNY2u/nwp7qVCVSuTgBVBxSKbze8c5mfgBD9Vm5/CTjNVAa9rWSYAKNxdpM8SZ07nLfg2MikYTJbGYjp+iSNcgQnuCLieUU+JHxGqFUA3iDopWDzFCv2K8tfBK1wVG4E8QjC5d5wNUsQOK8CCIqVfaVhN2EezCtmd+EZY1ok/MTAAmZMYxR9wXG4sakXcFaPn8xAaz0vsRfjboZc+tamaMAYPXZeFWhi7CmHAbxfPtekVxrP0v9GnTC0jFlrqaeSazNb9QQhl2GGa0hBDICHPtLB9e6oSTPqYphPYhpYqYdjH/zsybF901PQtmnq3z/owNfVguNR0CaNIkhjI8SLhUX0+S2DPUt7jFiQVj8BH9RRVmSg48ppC/OROmtovU1IqawM Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/1/26 13:20, Lance Yang wrote: > > On Wed, Apr 01, 2026 at 01:00:13PM +0200, David Hildenbrand (Arm) wrote: >> On 4/1/26 12:53, Lance Yang wrote: >>> >>> +Cc Deepanshu >>> >>> >>> Afraid not, it closes the remove_migration_ptes() -> >>> deferred_split_folio() race, but opens a new one with the shrinker, IIUC >>> >>> Once dst is on the deferred split queue, deferred_split_scan() can >>> pick it up immediately. The shrinker unconditionally dequeues every >>> folio it visits: >>> >>> list_del_init(&folio->_deferred_list); /* always */ >>> >>> Then for a non-partially-mapped folio, if folio_trylock() fails >>> (dst is still locked by migration), it falls through to: >>> >>> next: >>> if (did_split || !folio_test_partially_mapped(folio)) >>> continue; /* not requeued, dst silently lost */ >>> >>> so it is *not* requeued. >> >> How is that different to the shrinker just trying to lock the folio before we >> unlock it and failing? The race already exists? > > Ouch, you're right, I was wrong - the trylock drop is a pre-existing > issue, not caused by the reorder ;) > >> >> To sort out that race a trylock must not result in the folio getting >> discarded. > > Nice, LGTM! > > Given that the "trylock -> drop" behavior seems to exist already today, > do you think it's worth fixing that together with the reorder? I'd do it in a single shot if possible. Can you craft something? (cc stable etc) -- Cheers, David