From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 931FFCDB466 for ; Thu, 25 Jun 2026 06:46:17 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 875336B00B9; Thu, 25 Jun 2026 02:46:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 84C616B00BA; Thu, 25 Jun 2026 02:46:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 73BDA6B00BB; Thu, 25 Jun 2026 02:46:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 504556B00B9 for ; Thu, 25 Jun 2026 02:46:16 -0400 (EDT) Received: from smtpin24.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id D0278405FC for ; Thu, 25 Jun 2026 06:46:15 +0000 (UTC) X-FDA: 84917500710.24.6B03808 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf03.hostedemail.com (Postfix) with ESMTP id 0E39120009 for ; Thu, 25 Jun 2026 06:46:13 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=iV4Ydx7Z; 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; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782369974; b=kXd/mPe1huZs9n3gM7t9VQKqCUeaIDJf8PaqUgNGCWkU75iS+2dmbAEbvqILdbA5rH3UHJ d7Vj326ihJp9UNbTviP60hzhj5qapGUiWvg3Vt4yy268WFpBB5Ou3POtpgm9od1uU4amXJ bPzQsH8BInXuAVTjRhOxcZwJN7i9qGk= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782369974; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=9q6EIQf7iznyig2evji5XbOB/64u93bLawrJvslC1Vs=; b=WJ8L+xY5J3xUyEwZ4M5v1uaIxOl/a/EF25p+iXCcEErCdIzUZHpBNzfbB08w7MXouJ7MOb 1QyMVkd54w9oBfyCXhmgV7VC4P4aZbJg0uuHRSrJVnZwwfa75n3iS8oRmn9pyug4BB3+f0 /YR3q+Vnw5haAF4kTAxSSJgvN2ZbYKk= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=iV4Ydx7Z; 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 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 3D35F42AEC; Thu, 25 Jun 2026 06:46:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BEDE11F000E9; Thu, 25 Jun 2026 06:46:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782369973; bh=9q6EIQf7iznyig2evji5XbOB/64u93bLawrJvslC1Vs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=iV4Ydx7ZGplsvRZlB2I9+aX0jI+3RmZTKd1altCskoLzMtZ+2eHTYUXd/9Mjmb8QM pUjgH1oS+Ap2v69p1vE0rCyy3/ldMWscLbGB4h979v5oYH32xNehrRkOu4nn+js10/ FuUOz4Qx4MR0BdiQ+sOeV5RGXmSYJtSvsnkd9H0oAm1i6kJN6XzbftmFGB9X8WQPi9 HAN+Ll2UyhSqmwyekSbg6JsuvN1ILBVdY8NHzzeTA+5CrX3h3A4cIiRiaFhM4JjAXN +F76gVJZkXdz632qWRQ1qgYKyT7+ZW4kYy0do5vzKHr4w6/nj/fvoNEXEme7g65wja TETOPSmW3C+jw== Message-ID: Date: Thu, 25 Jun 2026 08:46:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] mm: assert exclusive nid/zonenum bits at the page/folio access sites To: Hui Zhu , Andrew Morton , Lorenzo Stoakes , "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 Cc: Hui Zhu References: <20260625053958.918738-1-hui.zhu@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: <20260625053958.918738-1-hui.zhu@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0E39120009 X-Rspam-User: X-Stat-Signature: szihbfdfimd3hhbs8y8xo3wagszweb1i X-HE-Tag: 1782369973-281421 X-HE-Meta: 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 ODTxj7PY bCZP16hWAoEZ+rgSqzHZrAPrGRhWgqiRlosUKcGEXdeHkxcZKQrRJ1l2/fZcS9Xl1kTQh97fLRXgAkdPMFYf9NdOaI/4EFW5JrAwGvf9lXZfPKOBpCMCbgC1cJcs7c/KLhRBwGIKIh5VplbPxF4UGbLjzBYnbGgqH8f0ENkysYR1VGsbckTWD8VeLvrbzs1aC4dvTHj8qy3xcxP+RKJwceRjLTVOnBUJhTbgDx/oAmPI9TzVon7AIvEr+onSvnZQgseqt0i/n0M4a21M0rJXXY0L1L0XUs813c0CtInO5ZCA6h3iZ9Sy+FAzTWfl0NZhssdSeoTaEOOK4W34= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/25/26 07:39, 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. Is that the case? I thought the existing ASSERT_EXCLUSIVE_BITS() reliably worked before? Maybe the compiler optimizing out a local copy sorted that for us. > 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 > --- > Changelog: > 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 | 9 +++++++++ > include/linux/mmzone.h | 3 ++- > 2 files changed, 11 insertions(+), 1 deletion(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 485df9c2dbdd..56b39194605a 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2294,15 +2294,24 @@ static inline int memdesc_nid(memdesc_flags_t mdf) > } > #endif > > +#ifdef CONFIG_NUMA > static inline int page_to_nid(const struct page *page) > { > + ASSERT_EXCLUSIVE_BITS(PF_POISONED_CHECK(page)->flags, > + NODES_MASK << NODES_PGSHIFT); Performing the PF_POISONED_CHECK() twice is a bit odd. One time is sufficient, maybe simply before both statements separately? > return memdesc_nid(PF_POISONED_CHECK(page)->flags); > } > > static inline int folio_nid(const struct folio *folio) > { > + ASSERT_EXCLUSIVE_BITS(folio->flags, > + NODES_MASK << NODES_PGSHIFT); > return memdesc_nid(folio->flags); > } > +#else > +#define page_to_nid(page) (0) > +#define folio_nid(folio) (0) > +#endif > LGTM Acked-by: David Hildenbrand (Arm) -- Cheers, David