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 7E9093F9277 for ; Wed, 8 Jul 2026 08:04:53 +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=1783497897; cv=none; b=AiJ+GlaO0B3OJ7+HE66to9fJl/qOuUOdnaPtHAt6aJYLebzFxeQ95/V13+F3i0Eaa9Ob1n/ZGuEDqmLZfBcZS7vyT/gSbItGqeAS4UkDYBcrIRuy+eNOfkzmE1pLEgAqxYw+iAIwCDYKQdnsaL8MiKTyTgERCw3AoIbK47asLIs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783497897; c=relaxed/simple; bh=dkduNr+VYs/sAsyM8cDaQhL46f6F+VnkMO9KRggQgLo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AS24gWh3NcKUvxnus+SiEYdf7eFAwS6UhTSuDJG9D6jhQm68ZarzOSrlQVzciDB5YzfkHGhzdBbP4fHCPtD3JAYWxQU2SUTn4prfy1T//jXN8clbyeUOxSmahmI2/024qmBE4HCWfoGOSgueFTKTOtfSMmFiYU75HoLttcCnu7c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=D4QGuiEW; 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="D4QGuiEW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A225D1F000E9; Wed, 8 Jul 2026 08:04:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783497893; bh=i+KcHVGfx4TQ7GeqLxiyIT2kRa9bqeUsL1z7l7Z/8gQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=D4QGuiEWjdQ6+wVyqz6pkTXQZi/Pa0pp9z+DKm8Wyzl96jzEvp6Bx+oU2fhETUKWE sMl1hY7yJetN3a3voHlhb04YYYWs/9ZVcP34zze1TcD9pXj7fhBOz/9kiFLcAis7F9 ByN+y8fvGHxWXLelMsK3weZIjpa/qmgGpvdYG4yJA3nxA40qPkzhMGxOzVk/TY78rA k+85/G9LbNrLs9ITl1cWuEEKZlnVxC3fATDmQIgM1B2w/3eFTRxmerNPGHpW1o1Tj7 89/jOn/87GsoDN/17st5/u7/hh702+2G/v1XNZnvk7oA4Fr0MK4e6d1eGPG2sBa+GW fv4kLCADplgxQ== Message-ID: <73c67890-0048-40ff-9314-81944a8dfdb8@kernel.org> Date: Wed, 8 Jul 2026 10:04:45 +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 v10] mm: fix ASSERT_EXCLUSIVE_BITS by passing memdesc_flags_t by pointer 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: <20260708021525.627503-1-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: <20260708021525.627503-1-hui.zhu@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/8/26 04:15, 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 race is benign: nid/zone bits are set once at page init and never > overlap with PG_locked. However, ASSERT_EXCLUSIVE_BITS() inside > memdesc_nid/zonenum() was checking a by-value copy of the flags word, > not the live page->flags, so it failed to annotate the real access. > > Change memdesc_nid(), memdesc_zonenum(), memdesc_section(), and > memdesc_is_zone_device() to take a const memdesc_flags_t * and update > all callers to pass &page->flags / &folio->flags, so > ASSERT_EXCLUSIVE_BITS() operates on the actual shared word. > > Guard the ASSERT_EXCLUSIVE_BITS() call in memdesc_zonenum() under > ZONES_WIDTH != 0 to avoid a zero-mask check on configs where the zone > field is absent. memdesc_section() needs no such guard, since > SECTIONS_WIDTH is never 0 wherever SECTION_IN_PAGE_FLAGS is defined. > Under CONFIG_NUMA=n, memdesc_nid() itself is stubbed to "return 0" > instead of reading page->flags, since NODES_MASK is 0 and the check > can never fire; page_to_nid()/folio_nid() now just call memdesc_nid() > unconditionally and rely on that stub, instead of duplicating the > CONFIG_NUMA split at each call site. > > Co-developed-by: David Hildenbrand (Arm) > Signed-off-by: David Hildenbrand (Arm) > Signed-off-by: Hui Zhu > --- > Changelog: > v10: > According to the comments of David, drop the redundant CONFIG_NUMA split > in page_to_nid()/folio_nid() and remove the SECTIONS_WIDTH != 0 guard > around ASSERT_EXCLUSIVE_BITS() in memdesc_section(). > v9: > Add the SECTIONS_WIDTH check to memdesc_section. > v8: > According to the comments of Andrew, include kcsan-checks.h in mm.h. > Incorporate David's patch that switch memdesc_nid(), memdesc_zonenum(), > memdesc_section() and memdesc_is_zone_device() to take a const > memdesc_flags_t * instead of using a per-accessor macro/call-site hack. > Update all callers accordingly and extend the same exclusive-bits check > to memdesc_section() and memdesc_is_zone_device(), guarded by > SECTIONS_WIDTH != 0 / reusing ZONES_WIDTH != 0 to avoid zero-mask checks > on configs without the corresponding field. > v7: > According to the comments of Sashiko, restrict the memdesc_nid() macro > to CONFIG_NUMA, keeping a plain "return 0" static inline stub otherwise, > and re-add a local page pointer in page_to_nid() to avoid evaluating > PF_POISONED_CHECK(page) twice. > v6: > According to the comments of David, turn memdesc_nid() from a static > inline function into a macro so ASSERT_EXCLUSIVE_BITS() can check the > caller's page->flags/folio->flags directly. > 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/asm-generic/memory_model.h | 2 +- > include/linux/mm.h | 28 ++++++++++++++++++++-------- > include/linux/mm_inline.h | 4 ++-- > include/linux/mmzone.h | 26 ++++++++++++++------------ > mm/page_alloc.c | 6 +++--- > mm/slab.h | 2 +- > mm/sparse.c | 2 +- > 7 files changed, 42 insertions(+), 28 deletions(-) > > diff --git a/include/asm-generic/memory_model.h b/include/asm-generic/memory_model.h > index fd74de50b054..c6b4eafaf4cb 100644 > --- a/include/asm-generic/memory_model.h > +++ b/include/asm-generic/memory_model.h > @@ -53,7 +53,7 @@ static inline int pfn_valid(unsigned long pfn) > */ > #define __page_to_pfn(pg) \ > ({ const struct page *__pg = (pg); \ > - int __sec = memdesc_section(__pg->flags); \ > + int __sec = memdesc_section(&__pg->flags); \ > (unsigned long)(__pg - __section_mem_map_addr(__nr_to_section(__sec))); \ > }) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 2101e5205fc0..01683d50b3cd 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -37,6 +37,7 @@ > #include > #include > #include > +#include > > struct mempolicy; > struct anon_vma; > @@ -2286,22 +2287,32 @@ static inline int page_zone_id(struct page *page) > } > > #ifdef NODE_NOT_IN_PAGE_FLAGS > -int memdesc_nid(memdesc_flags_t mdf); > +int memdesc_nid(const memdesc_flags_t *mdf); > #else > -static inline int memdesc_nid(memdesc_flags_t mdf) > +#ifdef CONFIG_NUMA > +static inline int memdesc_nid(const memdesc_flags_t *mdf) > { > - return (mdf.f >> NODES_PGSHIFT) & NODES_MASK; > + ASSERT_EXCLUSIVE_BITS(mdf->f, NODES_MASK << NODES_PGSHIFT); > + return (mdf->f >> NODES_PGSHIFT) & NODES_MASK; > } > +#else > +static inline int memdesc_nid(const memdesc_flags_t *mdf) > +{ > + return 0; > +} > +#endif > #endif > > 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); > + > + return memdesc_nid(&p->flags); > } Nit: Why not keep it as return memdesc_nid(&(PF_POISONED_CHECK(page)->flags)); Apart from that Acked-by: David Hildenbrand (Arm) -- Cheers, David