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 C0C3538911B; Mon, 29 Jun 2026 06:49:55 +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=1782715796; cv=none; b=fyaB7jfOjiKgFW6ebkIqcGxjnQe2kvUTUqiaq1k06m8GA+z+/mQs/cH1KUvcbw5JwfUqJ5b2b+EPu6vJVO6clzd1rgrFNyiI8+MJ7uFVKT4FdrSdbUjRxk/d8YMfhLC4XLuYh7DwRTqn2af80O9iAGu5xs3xE04XYAh2xSr0lrY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782715796; c=relaxed/simple; bh=OnUS1kfbHz14+DdTTxLXyZtmCFRu2rWn1HV2ntAIXd0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=B1rDNzt9kWanDvRIVp7iaXWV9I3+jumNcGCV3p1i1FqtSpVz83veo4j+7Yjhms5CQGXHw+r8KK+mH4rDB8mSSHMSBpnYtM86xasn7y/TvR/uu69SCgYzY3uljuGpDFmF6wQymgHdLBa857w69Kh4bUSQQpPE8uMOZRbFdDa9354= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kBYaXA3n; 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="kBYaXA3n" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2D5A1F000E9; Mon, 29 Jun 2026 06:49:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782715795; bh=3rqo+iGnNiPi7WUkA3ir659tVYxJHbxTA/cjOOBMrVA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=kBYaXA3neQO8Uwt2EmclV43XV0y6FxNDWsMHtcixzh4xUbZjwzxaEVsSL74hOvfK8 dAX0Ukj69TNlsNYunSnVKurCP3ZKtJn6IEVG8w0mXE1+7vDN30gwBoQGuHJ4yT+6Xy YgusRPmqGicsY0s3XbM53jANeUhGkeK+mxHHMS/WuZo/8X3QAJQQ5GKtuScy0CW8nl UMfoCtc/C1ev6M1xvg8fvsZM6prtfnsgtmiXTchfMahiOzYIB+EuJ7+gyA+sA4Psaq VR2wRiPleHLAJiTWvcwXf6AKdPPpBrRNM/LIPQcEJi+LROBqFdvmPjOpyFAIKMonPf WmVDV060OILng== Message-ID: <0b5f8b4b-d7dc-4b79-9555-a5b36265f3a9@kernel.org> Date: Mon, 29 Jun 2026 08:49:37 +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 0/2] mm: memory-failure: fix HWPoison flag race with non-atomic page flag ops To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: Miaohe Lin , Naoya Horiguchi , Andrew Morton , Oscar Salvador , Andi Kleen , Hidehiro Kawai , Rik van Riel , Vlastimil Babka , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Hao Li , Kiryl Shutsemau , Byungchul Park , linux-mm@kvack.org, linux-cxl@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 Content-Transfer-Encoding: 7bit On 6/28/26 23:45, Michael S. Tsirkin wrote: > I don't like it that we are adding overhead to the good path for > the benefit of memory failure, which never triggers on many systems, > but I don't have a better idea. Pls take a look. As I said on Friday. "It's also doesn't address the mf_mutex implications and the x86 thingies I mentioned. ... I'll either take care of that myself or find someone that can work on this with attention to all details. " This is nothing to vibe-code. This needs a real expert. > > Non-atomic page flag operations (page->flags.f &= ~mask, __set_bit, > __clear_bit) can race with atomic TestSetPageHWPoison() in > memory_failure(). The non-atomic RMW reads flags, memory_failure() > atomically sets HWPoison, then the RMW writes back the old value > without HWPoison, clobbering the bit. > > The race was confirmed by injecting a cpu_relax() delay between the > load and store of the non-atomic RMW in __free_pages_prepare, then > running concurrent MADV_HWPOISON injection. The clobbered HWPoison > bit was observed repeatedly. > > This series fixes the race by: > > 1. Having memory_failure() call synchronize_rcu() + retry after > setting HWPoison, so that any in-flight non-atomic RMW that > read the old flags value completes before we proceed. > > 2. Wrapping all non-atomic page flag operations in > rcu_read_lock/rcu_read_unlock (CONFIG_MEMORY_FAILURE only), > so that synchronize_rcu() actually drains them. > > Performance impact (page alloc+free microbenchmark, 200K iterations, > 20 runs, KVM guest, error bars are 3-sigma): > > !PREEMPT_RCU (x86): > insns/iter cycles/iter > base: 12237 +/- 1 17954 +/- 136 > patched: +22 +/- 1 -124 +/- 122 > (+0.18%) (within noise) > > PREEMPT_RCU: > insns/iter cycles/iter > base: 12512 +/- 3 18541 +/- 214 > patched: +95 +/- 3 -12 +/- 161 > (+0.76%) (within noise) > > When !CONFIG_MEMORY_FAILURE, all wrappers compile away completely. > > Suggested-by: David Hildenbrand No ;) -- Cheers, David