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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782200536; 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=ZtWmTuyVYWDd7wNzN5g6THdg+A3Pzvxm/xjDFHxskok=; b=TZ1kLBEGB+dLCB5ixHqMmNpeHMIuA4Ol+HQmZa0vTFZtbfPACoeQpe9XlH6nCkDc2RJjCY BJNKcHX8EN0xtNhZUfUeGNmc4Synx1Z0fwrEGbqmcgtTGXOHh9xMB/zXa56WfJwOxGAqfS axlxnYJl2UVS5NWXfxSNcywzkgIzLck= From: Hui Zhu To: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R\. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Hui Zhu Subject: [PATCH] mm: avoid KCSAN false positive in page_to_nid() Date: Tue, 23 Jun 2026 15:41:57 +0800 Message-ID: <20260623074157.578113-1-hui.zhu@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 1C53A40016 X-Rspam-User: X-Stat-Signature: aukixyekq1mpjx68xnfo1xn1ed5amnh7 X-HE-Tag: 1782200538-66440 X-HE-Meta: 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 Lbaom5YA TaCz08zyELfuyPErrtY5uBAsiB3Ol3AyVLIyWLp5+0yiYInSatNCQGsqjoiS016NiP28+LnU60X7XxH0vcOcdFzAbxfgrN+ndlnCFmS0m8zbLG6m3GRjRz8EKjip/INw3erXDZV9kDCYJ13Lccajbrf7f4BWgXlm/y4XpKTmasAqw0osFCdCy9/TfO2XZOMY9gQ2wEAKClz0KR0tRiseTYB9v+ehykQWq0dlFvNBhAWSrCOgzWeSxoQ8m33OnABOftmmpf3llLY3pZrGEg3dJqTMPK0YrmPmw4WXki/gRRTuq3F4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Hui Zhu KCSAN reports a data race between page_to_nid() reading page->flags and folio_trylock()/folio_lock() doing test_and_set_bit_lock(PG_locked, ...) on the same word from another CPU, e.g.: BUG: KCSAN: data-race in __lruvec_stat_mod_folio / shmem_get_folio_gfp The node id occupies a fixed, high bit-range of page->flags that is set once when the page is initialized and never modified afterwards, so it can never overlap with the low PG_locked/PG_waiters bits touched by the folio lock path. The race is therefore harmless: page_to_nid() always returns a consistent value regardless of how the read interleaves with the lock bit ops. Wrap the flags read with data_race() to tell KCSAN this race is intentional and benign, consistent with how page->page_type is already annotated for similar packed-field accesses. Signed-off-by: Hui Zhu --- include/linux/mm.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 485df9c2dbdd..122d3b39369f 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2296,7 +2296,14 @@ static inline int memdesc_nid(memdesc_flags_t mdf) static inline int page_to_nid(const struct page *page) { - return memdesc_nid(PF_POISONED_CHECK(page)->flags); + /* + * The node id occupies a fixed high bit-range of page->flags + * that is set once at page init and never changed afterwards. + * It cannot overlap with the low PG_locked/PG_waiters bits + * that folio_lock()/folio_unlock() concurrently update, so + * this data race is benign. + */ + return memdesc_nid(data_race(PF_POISONED_CHECK(page)->flags)); } static inline int folio_nid(const struct folio *folio) -- 2.43.0