From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6F3704C653B for ; Wed, 16 Sep 2026 15:48:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789573697; cv=none; b=X+E3ocMpi7tvVLIVgtMp/UBaDhlOIm9S3+mwNCd1DXsSSmsHbCqYWMmhoFAbpVye/PFEgQp4jIPAzCbrQLk7t2/79B4TYb4AXiIMWHxxgWeX2qFNmmNlDIIOEmJboYrSFdLXQ/fvdDNN49ansb56drORToKmgcaYn7X3wIJFHtg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789573697; c=relaxed/simple; bh=RddIrLDSRmumbLHD027lBYnFZSknzjsQycSlUhA7uL0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=QQ4vnJBOTvybhax0mUjc8VMm++XK3y9BUuOPcYkeKVgHWRa0MxmZeESxMO7wjU45zRtHkhuISaNVC+LnU6UeTOtmcJ1+faFxQJNQEI4GTJltuyPi+y6uCQKVbWPYqZo+WnRQMT9xcBG/oKZRGl2wq7UWCNIaPa0Zem60aO2mYHI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NFp2cwYO; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NFp2cwYO" 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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