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 7006A32A3C9; Tue, 16 Jun 2026 17:46:55 +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=1781632017; cv=none; b=ahOcWjT9c8PmfIHMQA3sxOgD7GCDoBSbgdek2QvknQwlQeigcsYGNvjy/0hTxLHWXRMygQm+dNaU/fyn3rLnICMjaufRviSpuNw4JJ//olF6JqbmQV+ZQWuUP7/oLDMHKVUNVyU9VitZwkmeHZlqm9+YtG4ehZVb5GbC4C9qIKA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781632017; c=relaxed/simple; bh=PgjK+NSLI7clWy3j+HKaLCLEC2NK1GV49xQS3O1lpG8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=txmIG9uJFbeptCqXBL38XjPEIjJ2cmYv65Qs90WYs13+H0+wyo5/LYxNLIpHc879P8uyf/C2c58tlZsFZeZbiPwz3M2PgDRIwV1Wx4RFz5zZOZFDQUOt1eqjA7+JvKBG6FIOeGD518Sl7vN18a+tBjEy9S6t1Bcd7EEi01JgmxY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=lhc2VK1A; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="lhc2VK1A" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E2B561F000E9; Tue, 16 Jun 2026 17:46:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781632014; bh=9bi5iXuUG0g1wbh60r6gUQrKVLEs4TQDwjIvPNIdnMw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=lhc2VK1AgTkT8LX52aK5+2DdO6+cWH0Giun54hrNm2UZtb6JkIghB/nxFuMS1v9mW e2MzlZK5Az7aEHvjIwRmWhrxJDYGrgLJM/VJ/RPOHQKS366vqGUGR0JQyGf4aSUaef f4LACfrodcSa+NcadiRTVSmGyesRZGUfowwup1eE= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, SeongJae Park , Fernand Sieber , Leonard Foerster , Shakeel Butt , Andrew Morton , Sasha Levin Subject: [PATCH 6.1 329/522] mm/damon/ops-common: call folio_test_lru() after folio_get() Date: Tue, 16 Jun 2026 20:27:56 +0530 Message-ID: <20260616145141.221061388@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145125.307082728@linuxfoundation.org> References: <20260616145125.307082728@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ 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/ops-common.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c index 0b75a8d5c70684..cea4401e95a35e 100644 --- a/mm/damon/ops-common.c +++ b/mm/damon/ops-common.c @@ -23,10 +23,10 @@ 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