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 EA6A73B0AF0 for ; Thu, 25 Jun 2026 12:08:45 +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=1782389327; cv=none; b=SLLQarXF0uLu0Hor/KBrxvLtyoTTxcFMmalGZmkMRW9sFBg6vGt4SXJzJo4PuG1UMnYwgy3FpWlQnY+ztwXRmlWN7dDyPbHcSPHk16Ycod/EWZ2y78SyZk6O7J1CFZfj0a00xCB4YEKBp9B5oGt/ZJHQK5GOJdstCH25Wutpi2Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782389327; c=relaxed/simple; bh=PIp3U8vUejWwP5HGO3mrdaqNlmaCinxU9InpanK96TA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=eMTT1FB7L1T0r7D0DhCu68s6bA8C9b8Oz8YPx/1K/niV7TFO2nedBbWLktZvfFyX/z+tvJKfgn1pu8LocLk/MFJRgf9zeZD70a4qBY1mrKGBWRonI7BNQjhlNLSlbnBztHxjVo9dg++6UcFqPa7HITjWqM7upwmUjrP9uGlV8ZE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FGW6k/JE; 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="FGW6k/JE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6F9B81F00A3D; Thu, 25 Jun 2026 12:08:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782389325; bh=bUMnbm9PMtjxsIHIOqPvFeqdrsxsns25/0hnbpw0h1E=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FGW6k/JEa1F29Biq8P0vCqd0k0Iz3i4FBze/O3ByQhUqGW3nmARz7FElqJf5IiP6Y 9yfZPETp1G1DBFaYy2/Jp5qdeRMDJhDuR+3lJ3Ws4QF1C/MKAxEP6BxfU+y+rhLoYx iSVynPoCQm3SjVeqSOMTBTeDVJxZRbSIPCXq3dj2ooNgB/1R95WRbGT7c2P0TCQmoG b3Mqj9wg65NLkOBLmoZhLG+PiNzPCsuV0F3m3T7hsp89RH55eGAS1YXrrOpyayC3vx xrnAIhQQ2zAuV4Wui+vkhZ0adzwFo8lXc8E0rlzYHV/Am1oIDNTPNa3nsu1yRz5X37 LZM0i0uAKvkbA== Message-ID: <7efb57b0-7205-440c-8638-2ec5354aacce@kernel.org> Date: Thu, 25 Jun 2026 14:08:39 +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 v5] mm: assert exclusive nid/zonenum bits at the page/folio access sites To: Lorenzo Stoakes Cc: Hui Zhu , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hui Zhu References: <20260625071830.996043-1-hui.zhu@linux.dev> <2c4dd46a-4755-4bf5-8f14-2d73eb356e3e@kernel.org> 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 6/25/26 14:07, Lorenzo Stoakes wrote: > On Thu, Jun 25, 2026 at 01:53:14PM +0200, David Hildenbrand (Arm) wrote: >> On 6/25/26 09:18, Hui Zhu wrote: >>> From: Hui Zhu >>> >>> KCSAN reports a data race between page_to_nid()/folio_pgdat() reading >>> page->flags and folio_trylock()/folio_lock() concurrently doing >>> test_and_set_bit_lock(PG_locked, ...) on the same word, e.g.: >>> >>> BUG: KCSAN: data-race in __lruvec_stat_mod_folio / shmem_get_folio_gfp >>> >>> The node id and zone id occupy fixed bit-ranges of page->flags that >>> are set once at page init and never modified afterwards, so they can >>> never overlap with the low PG_locked/PG_waiters bits touched by the >>> folio lock path. >>> >>> ASSERT_EXCLUSIVE_BITS(mdf.f, ...) inside memdesc_nid()/memdesc_zonenum() >>> checks a by-value copy of the flags word, not the actual shared >>> page->flags/folio->flags being modified concurrently, so it doesn't >>> reliably assert anything about the real race. Move the assertion to >>> page_to_nid(), folio_nid(), page_zonenum() and folio_zonenum(), where >>> flags is dereferenced directly from the page/folio. >>> >>> On CONFIG_NUMA=n, NODES_MASK is 0 and the old memdesc_nid() body >>> folded to a constant, so page->flags/folio->flags was never actually >>> read. ASSERT_EXCLUSIVE_BITS() is a real runtime check that can't be >>> folded away, so doing it unconditionally would add a pointless read >>> of page->flags/folio->flags and a check that can never fire. Keep >>> page_to_nid()/folio_nid() as plain "return 0" static inline stubs >>> under CONFIG_NUMA=n instead. >>> >>> Signed-off-by: Hui Zhu >>> Acked-by: David Hildenbrand (Arm) >>> --- >>> Changelog: >>> v5: >>> According to the comments of Sashiko, guard the ASSERT_EXCLUSIVE_BITS() >>> calls with #ifndef NODE_NOT_IN_PAGE_FLAGS (for nid) and #if >>> ZONES_WIDTH != 0 (for zonenum). >>> According to the comments of David, avoid calling >>> PF_POISONED_CHECK(page) twice in page_to_nid(). >>> According to the warning of lkp, switch the CONFIG_NUMA=n >>> page_to_nid()/folio_nid() stubs from macros to static inline functions. >>> v4: >>> According to the comments of Andrew and Sashiko, set >>> page_to_nid()/folio_nid() as static inline stubs returning 0 >>> under CONFIG_NUMA=n. >>> v3: >>> According to the comments of Andrew and Sashiko, move >>> ASSERT_EXCLUSIVE_BITS out of memdesc_nid()/memdesc_zonenum() >>> into the page/folio call sites. >>> v2: >>> According to the comments of David, remove useless comments and use >>> ASSERT_EXCLUSIVE_BITS() in memdesc_nid() instead of data_race() in >>> page_to_nid(). >>> >>> include/linux/mm.h | 23 ++++++++++++++++++++++- >>> include/linux/mmzone.h | 7 ++++++- >>> 2 files changed, 28 insertions(+), 2 deletions(-) >>> >>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>> index 485df9c2dbdd..772bd1fc6fe7 100644 >>> --- a/include/linux/mm.h >>> +++ b/include/linux/mm.h >>> @@ -2294,15 +2294,36 @@ static inline int memdesc_nid(memdesc_flags_t mdf) >>> } >>> #endif >>> >>> +#ifdef CONFIG_NUMA >>> static inline int page_to_nid(const struct page *page) >>> { >>> - return memdesc_nid(PF_POISONED_CHECK(page)->flags); >>> + const struct page *p = PF_POISONED_CHECK(page); >>> + >>> +#ifndef NODE_NOT_IN_PAGE_FLAGS >>> + ASSERT_EXCLUSIVE_BITS(p->flags, NODES_MASK << NODES_PGSHIFT); >>> +#endif >>> + return memdesc_nid(p->flags); >>> } >>> >>> static inline int folio_nid(const struct folio *folio) >>> { >>> +#ifndef NODE_NOT_IN_PAGE_FLAGS >>> + ASSERT_EXCLUSIVE_BITS(folio->flags, >>> + NODES_MASK << NODES_PGSHIFT); >>> +#endif47 >> >> This is getting ugly, really. We're leaking implementation details from >> memdesc_nid() into folio_nid(). >> >> Maybe just turn memdesc_nid() into a macro where we can just do that check >> internally? Not the best thing in this world, but better than this here. > > Could also do: > > if (!IS_ENABLED(NODE_NOT_IN_PAGE_FLAGS)) > ASSERT_EXCLUSIVE_BITS(folio->flags, > NODES_MASK << NODES_PGSHIFT); > > But not sure if it's that much better. It's still making an assumption of what the memdesc function we're calling will do. -- Cheers, David