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 E0B72212564 for ; Thu, 25 Jun 2026 07:19:01 +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=1782371943; cv=none; b=SNFFzw89QB4ka0lkHL0ufBbBj+bPmDcWWcK3+EF2lpUDYBrWnn3hXmFYCDRUQ5FcSyzJNwBePoVCvTHYjCM9119wRCUhkHs8Sg6T5XD3Joguab0yBGTCVguDiM8HFPUF7w+a2q6bAD6pKBTxNgD42lw57AfATjsOEaTTpUo3dCo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782371943; c=relaxed/simple; bh=qBVIt8peOehkXbkshkUkuhG6kczZ7xa+zLnuIjeNb9E=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=SKov+RBqhoYl2AxFph328kXaCwzDQv4mnWUW8WnOh/BQl1RE+XcN1rg6Qr9CE5BeaXKVF8UxrBjaci9CCRw19jmxLBBzOv2GPAMQO53kOD+TfXTCVvre93RoBCvsfX4UX/UaiR/fOOr5UAwuyCBu/e5tU1z3YANgqtNTMYuZQuc= 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=PqO7Ml3w; 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="PqO7Ml3w" 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=1782371940; 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=DtqYjf8o+h1s++eJw/fsOV0DeEGdtcrbKOFqYGZRieA=; b=PqO7Ml3wa+JfLzJlv1ArftxG904CUk8YpV39I/r32sfJPKf8Dh5TmPp4LIGyjUkNT4HLER koF9sKb7na0DZIsLR919G6MgcnoYfz3sQ5G9usEglaOj1Zg6fqSeL6/Wmti0IpRdk2eBFE SXlSyPzwWGsAyMLGryujVQ0+JwwGtSw= 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 v5] mm: assert exclusive nid/zonenum bits at the page/folio access sites Date: Thu, 25 Jun 2026 15:18:30 +0800 Message-ID: <20260625071830.996043-1-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 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); +#endif 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); } -- 2.43.0