From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) (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 386901DD0EF for ; Thu, 25 Jun 2026 05:40:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782366035; cv=none; b=ZNFWMcRLpfAtjDWYnIhJ0EjKiswX1Lj4VILRWdgz3j8WZLPBc3enwETEEAf5OPA1jkOAE7Qab4jhydvq5Z9KIpHy6m23OFFsZxoRucXT/1U6Xh2wq70sJVhdsWq5XD57ZGuwYquW9DK3zYcBvT3HuSOmfrnGI4IVzwaNp3Jrt7Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782366035; c=relaxed/simple; bh=dkNmRI+a+rVYtYwzQrj0lzmFpSR13D2oBGVa82qEC1U=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Dr/Y2ewCtD6TPd+IOFrYpkK7cTYrAiGnshgxwSadFJukPA6mqgZffa8dgixH2rarYpXTyV0zwKIJlXsoCDfJxls8Q4EHJEm2vo76ihxS7QUzYhTvfnnOH6rx38B5Fi1HsHhLIRhSbM7YA/LUMwCX0BPNCaiXbm5rTsy+ReiaRcc= 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=r4w4yPjo; arc=none smtp.client-ip=95.215.58.182 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="r4w4yPjo" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782366030; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=NkjLU/0Y0qQUoUyC3qszvMPUKNHSpAOvXGQbghzmUII=; b=r4w4yPjoXtja9+iHejy8uZx7iZPZEbTrog6OMqItNVZiuU4ijvWWg/M8jGyqbC56pHNAZd s/6So9b1bqjGyc+bdrMg09BjoDXGGG+GoWJx2oR7Ldv4wlPJbyW3iFuuTsmqGCwozOVMcN 42RBO01L3OC/ZF+ycXkaZPmpyBkhrug= From: Hui Zhu To: 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 Subject: [PATCH v4] mm: assert exclusive nid/zonenum bits at the page/folio access sites Date: Thu, 25 Jun 2026 13:39:58 +0800 Message-ID: <20260625053958.918738-1-hui.zhu@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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 --- 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); 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 #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..56dffa966343 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -1274,17 +1274,18 @@ 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) { + ASSERT_EXCLUSIVE_BITS(page->flags, ZONES_MASK << ZONES_PGSHIFT); return memdesc_zonenum(page->flags); } static inline enum zone_type folio_zonenum(const struct folio *folio) { + ASSERT_EXCLUSIVE_BITS(folio->flags, ZONES_MASK << ZONES_PGSHIFT); return memdesc_zonenum(folio->flags); } -- 2.43.0