From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta1.migadu.com (out-173.mta1.migadu.com [95.215.58.173]) (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 DE9B3279329 for ; Fri, 26 Jun 2026 05:05:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782450328; cv=none; b=XKza7Ol8bGtKEiwZK7VmaIg/6UhypV4hXeAulIcqjdEER0xT/PnxdvSe5/fFIupGO0JOE8JLuK6Dc2KG53/c62aY4LbtWpTnCvZzc06CR2BbmUPzLEH306K+xfhqy0UA07CSKSj9iOQAEYe2wA3U3n4meA4gSMgo/C63qwX1t9s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782450328; c=relaxed/simple; bh=9SFQpwrL6HnILWIon4FYupKg+DXde5CgS0QZP/WW7JM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=L/j8SSfqmsiOaGqT8V5/+FPgMi/b0Accu9hAEZXGn2v2TBfrGRSO2G5ZJ2KeVtBE4aerzYo8VeKu13ZaiP0FENecNN0Crzg9AykIfL8tZO60clhcZYufuRAb+bzzJZ9v4d6r2jCzgBrdMU6AHEQ6QfBiM0yU8AUSJcm1R9TbGN8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=kL8d4v0a; arc=none smtp.client-ip=95.215.58.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="kL8d4v0a" Message-ID: <925c8686-9ff6-44c1-9780-63bd7cd8a1c3@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782450313; h=from:from: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; bh=u7v0PPdOi6Pl4ejNu0hv7r7pLaNyzclPpil1+QtQ9Dg=; b=kL8d4v0aV7DDMvUYsPHOBhZqJmyWCtgnEifP1xb8Lm81nORYLNFhU9MTI36LrxV6kcHrfM nyccMjaKwGfzz4YYmbZciuqA8+g4mk416iv0tH3va/dcRXXk+xaRdUVkex/7tHlwIkVPZ0 nNRUVyjEldhtn1B30EduqeECwLlXuwc= Date: Fri, 26 Jun 2026 13:04:51 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v7] mm: assert exclusive nid/zonenum bits at the page/folio access sites Content-Language: en-US To: Hui Zhu , Andrew Morton , David Hildenbrand , 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: <20260626032012.1049667-1-hui.zhu@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Leon Hwang In-Reply-To: <20260626032012.1049667-1-hui.zhu@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 26/6/26 11:20, 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() > used to check a by-value copy of the flags word, not the actual shared > page->flags/folio->flags being modified concurrently, so it didn't > reliably assert anything about the real race. > > For zonenum, move the assertion out of memdesc_zonenum() into > page_zonenum() and folio_zonenum(), where flags is dereferenced > directly from the page/folio. > > For nid, turn memdesc_nid() into a macro instead, so the mdf argument > is expanded as the caller's own flags expression > (PF_POISONED_CHECK(page)->flags or folio->flags) rather than copied > into a function parameter, letting ASSERT_EXCLUSIVE_BITS() check the > real page->flags/folio->flags directly. > > 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: > 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/linux/mm.h | 25 +++++++++++++++++++++++-- > include/linux/mmzone.h | 7 ++++++- > 2 files changed, 29 insertions(+), 3 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 485df9c2dbdd..63fcf277b675 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2288,21 +2288,42 @@ static inline int page_zone_id(struct page *page) > #ifdef NODE_NOT_IN_PAGE_FLAGS > int memdesc_nid(memdesc_flags_t mdf); > #else > +#ifdef CONFIG_NUMA > +#define memdesc_nid(mdf) \ > +({ \ > + ASSERT_EXCLUSIVE_BITS(mdf.f, NODES_MASK << NODES_PGSHIFT); \ > + (int)((mdf.f >> NODES_PGSHIFT) & NODES_MASK); \ > +}) > +#else > static inline int memdesc_nid(memdesc_flags_t mdf) > { > - return (mdf.f >> NODES_PGSHIFT) & NODES_MASK; > + return 0; > } > #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); > + > + return memdesc_nid(p->flags); > } > > static inline int folio_nid(const struct folio *folio) > { > return memdesc_nid(folio->flags); > } > +#else > +static inline int page_to_nid(const struct page *page) > +{ > + return 0; > +} > + > +static inline int folio_nid(const struct folio *folio) > +{ > + return 0; > +} > +#endif > > #ifdef CONFIG_NUMA_BALANCING > /* page access time bits needs to hold at least 4 seconds */ > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index ca2712187147..1b4336098113 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1274,17 +1274,22 @@ static inline bool zone_is_empty(const struct zone *zone) > > static inline enum zone_type memdesc_zonenum(memdesc_flags_t flags) > { > - ASSERT_EXCLUSIVE_BITS(flags.f, ZONES_MASK << ZONES_PGSHIFT); > return (flags.f >> ZONES_PGSHIFT) & ZONES_MASK; > } > > static inline enum zone_type page_zonenum(const struct page *page) > { > +#if ZONES_WIDTH != 0 > + ASSERT_EXCLUSIVE_BITS(page->flags, ZONES_MASK << ZONES_PGSHIFT); > +#endif > return memdesc_zonenum(page->flags); > } > > static inline enum zone_type folio_zonenum(const struct folio *folio) > { > +#if ZONES_WIDTH != 0 > + ASSERT_EXCLUSIVE_BITS(folio->flags, ZONES_MASK << ZONES_PGSHIFT); > +#endif > return memdesc_zonenum(folio->flags); > } > Better to factor out a common macro alongside a comment for these two '#if'? Thanks, Leon