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a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1789573697; b=N+f4jQc7dpdg3PJhGpu9Y2NxIu1USH8wxO1z2Gg1QhrW/rydU4OLzInOD6uPV2iqP+R3Ri wiDhD8GgjOv60pB2iBn1YTC6pA+jEbpK3ZqUeiu6xXKW4MlUPyJaiCBQfQJBHPbJ1/Fjm0 dsodTcFUt8YRAY1jlEV6lz6SNKKeLKw= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=NFp2cwYO; spf=pass (imf24.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 8C765602CC; Wed, 16 Sep 2026 15:48:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 969B51F00893; Wed, 16 Sep 2026 15:48:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789573696; bh=gskwgGHRMM7t2Jel0JgW6huYm8F1pELSbv7bhAuvqqA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=NFp2cwYO6QAEFYHTGlepp6PIGgfQtTKWLqgWZWIBFrJ/4521Aomax5NAx6y+qpzA8 UFCri083JdJjCYTLoGovaX09FvKwqdHZr4XoQ6UEIEUtC3j63YzdV1qVCqynUpo1oJ nPPcmlWlKxuwfFAFJSADHodNAwStbFCHWyzxNMePkwTg/3z1pqI756Rx3k1jXU9pt/ QW3TceTrD52IsqnjCcB3Y9EdSPBaw/tgKFHYlt7a+4kIHwTbNVRgHgdsFMzEqK+qnU CIi65G1Gq3v6q8ESDLDpHtgas5HGG/L1PJXsAYvkQcTekNo2C2EsPmdotSnDnwrRNE jnXtPA2MntVMw== Message-ID: <7560715f-43fc-46ec-a860-4cc63ac4e51f@kernel.org> Date: Wed, 16 Sep 2026 17:48:11 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/mempolicy: use SRCU for the weighted interleave state To: Gregory Price , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, urezki@gmail.com, chenwandun@huawei.com, Matthew Wilcox References: <20260829015943.1258774-1-gourry@gourry.net> <20260829015943.1258774-2-gourry@gourry.net> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 26280180006 X-Stat-Signature: wd3x5b6js96b5zf1nk1i4w6j775krc9w X-Rspam-User: X-HE-Tag: 1789573696-440348 X-HE-Meta: U2FsdGVkX1+9U1NjL0naXBwWsb3qB93koTurpIhXbtkLQXWKS0AXpvDxkZGzvzDxL2oFtdLRaiwRIGbxIwHZHEUC9q7kvWf5/fBaPUW0r0PYZIfU4aO0zi44qBvKP8l9krVbnKORADcvGpjsbY/Fx3lEMQhdysKFRpMYxPHFacfclMGs3W2Q3QcCQfWcvoNZliPacFAl1EpGOA51rhv89p+vmmImBMmjm9Zkd9GkmFookIukpXuWWItidXsT+NapzOaWxmkN5L+Mlug4l34VuJyqjzEjDHYCKb2x8XQqP/9djzL5O4UHs7R7DfAQ8F0ltGtHJSA+P15Rkt19A9D+QoJkm6wKfU2CNN/0sPKKhrI4vO1xUwY8iJ2/8GhyQJfPZ+LY1eogi82i7JM4XXC5y4lFLPAfY7rEhmB2o5HLld5ZsLlRmRTF6ZpUldLUH0LkhtqpwkvxymVQw2iaxPY2XB5XW0L+forv4vmW6s83HPOKfahjMLxatNL0s1CJtxIiKl5WhqPCYvDIUveolIY6E8Ex9B2Ngh/1ueSFjq+bC/ZvewDase3DrIHMaUzdUKlRp57XqdyXmwK88Ry6JF+slNqGQu9YDTW9Eln8FAyp8OQkzv3MzrPtBzS0Qw/E2pMztVbrkyQTLGcMFCPRrQbvldGQqRug2fiDbVCzFGsbPbFgf7qPUyzGTotLt79NbMZ3h+JL5K8Ud/qlesQpCKayH94ZoexnQP4r+5sqc3ZDrqUWEL/aVtf8Ssz8weBzV9inX3EbcKiLJnx/tEvCnZfhP3DsvJbMjr64wfGnvnmQYDI577Sgi3cpzt4Jg25k8HsQI6Rd4taOUzvYfDW2OTh2R777jHfkKoO0M+MRE0t9yaqpjvxBnzEcuE2a0JzcDRY0pMsmHb+l9RwTEw53mPbeamKy4EZI+GIpwNBMkGxbtdseFL+KzYvfpXM+6dbLnIl4CpeS8vCJECH4Igb91j/ a/9JfXQJ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/29/26 03:59, Gregory Price wrote: > alloc_pages_bulk_weighted_interleave() copies iw_table into a scratch > array on every call so it can walk the weights outside of RCU. The copy > exists only because the loop may sleep in the page allocator and so cannot > hold rcu_read_lock(). > > Use SRCU to pin the global iw_table object and use it in-place instead. > > Retire through both flavors - call_srcu() for the sleeping readers, then > kfree_rcu() for the reference-less ones - so writers no longer block on > synchronize_rcu() either. > > Tested in a VM with KASAN, PROVE_LOCKING and DEBUG_OBJECTS_RCU_HEAD, > with a udelay() injected into the read section to widen the race against > concurrent sysfs weight writers, and placement checked against the > configured weights. > > Every retired state reached its callback. Swapping the deferred free for > a bare kfree() in the same test reports a use-after-free immediately. > > Suggested-by: Andrew Morton > Suggested-by: Matthew Wilcox > Assisted-by: Claude:claude-opus-5 > Signed-off-by: Gregory Price (Meta) > --- LGTM Acked-by: David Hildenbrand (Arm) -- Cheers, David