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 2C98B3B27DF for ; Mon, 15 Jun 2026 19:37:33 +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=1781552259; cv=none; b=ClJiqwq2U95FQjtppxBGC0KDlwoCDw3niFjMzeYMbO8EbHXjqO6tbaoPSws58sv6IbuExi3n8QE9kgBO7naGrvam895A6Z+R8Sral3LkrdtMU7RK7Ncz2jCOyiidcSsNRerczCVRELEazHPheVVRfx78exCx7aUs3lTpTvvXAg4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781552259; c=relaxed/simple; bh=hrO1p3Flczlpy63OXoBUozbBPvL34FX/Zlc6CkozlbI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=JIvB5z1JV7nDtwu+3J6i6Z/zha1aAuBEWAsPmjg00Vm5+1kLkReJf8qLc5iPXMpD+lRMpDzLwosOvHNSoG19IMw2OBsYnVOOUvX3ZyzhRBkvmLIWqpAVBZcs63xSXcap/+8id5Sa3TYFOjYXZO7/yxkDWiBg3NFaDru9fFj7xcc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CXNsInsv; 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="CXNsInsv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E9751F00A3E; Mon, 15 Jun 2026 19:37:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781552253; bh=MUJPp3ptbuvo28ndU79lO2ZThsS/yPH6M/1hFz/JeOY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=CXNsInsvTPahxm1DUtIYG6nAtVPR6iFBLQvvyMlxzQkex7hwoUgNVU4S3BbUeGQow 6bX1DVRjEmVfq/+OC4+sNczs17I/UEvenuYWMdF1V6efcTcFogXueTT3SYsxvBv7Yw mbPiMCiyu+CVkWY0M/z7g1kEuVpYn8k8p/cZedqh/XhVe1HGFlTCSdNi2Jmi77PrDS fisF6BM/MhVcvNG3bCsx283Hpt1FNKoh9Wke/iqaL1YmXMbTyae3T2j31+JW88mENM Ws0sqWph2ey08fNwiYYgf3L8xAYziwGa7HGibJXsFrC8/eE2uIvW2PsHeLi3vaNX4U Y2BQ2FlOzZbMg== From: Sasha Levin To: stable@vger.kernel.org Cc: SeongJae Park , Fernand Sieber , Leonard Foerster , Shakeel Butt , Andrew Morton , Sasha Levin Subject: [PATCH 5.15.y] mm/damon/ops-common: call folio_test_lru() after folio_get() Date: Mon, 15 Jun 2026 15:37:31 -0400 Message-ID: <20260615193731.2389762-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026061532-emu-stopped-b17a@gregkh> References: <2026061532-emu-stopped-b17a@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: SeongJae Park [ Upstream commit d6b8b02a27b3dd09ec12144322b3dac46d9bc9ef ] damon_get_folio() speculatively calls folio_test_lru() before folio_try_get(). The folio can get freed and reallocated to a tail page. In the case, VM_BUG_ON_PGFLAGS() in const_folio_flags() can be triggered. Remove the speculative call. Also mark folio_test_lru() check right after folio_try_get() success as no more unlikely. The race should be rare. Also the problem can happen only if the kernel has enabled CONFIG_DEBUG_VM_PGFLAGS. No real world report of this issue has been made so far. This fix is based on only theoretical analysis. That said, a bug is a bug. A similar issue was also fixed via commit 3203b3ab0fcf ("mm/filemap: don't call folio_test_locked() without a reference in next_uptodate_folio()"). I don't expect this change will make a meaningful impact to DAMON performance in the real world, though I will be happy to be corrected from the real world reports. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260525162256.8317-1-sj@kernel.org Link: https://lore.kernel.org/20260517234112.89245-1-sj@kernel.org [1] Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces") Signed-off-by: SeongJae Park Cc: Fernand Sieber Cc: Leonard Foerster Cc: Shakeel Butt Cc: # 5.15.x Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- mm/damon/vaddr.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c index 6d8036671e60e5..dbb0f0fb2e598c 100644 --- a/mm/damon/vaddr.c +++ b/mm/damon/vaddr.c @@ -383,10 +383,10 @@ static struct page *damon_get_page(unsigned long pfn) { struct page *page = pfn_to_online_page(pfn); - if (!page || !PageLRU(page) || !get_page_unless_zero(page)) + if (!page || !get_page_unless_zero(page)) return NULL; - if (unlikely(!PageLRU(page))) { + if (!PageLRU(page)) { put_page(page); page = NULL; } -- 2.53.0