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 3B2493AB27F; Wed, 15 Jul 2026 03:10:14 +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=1784085016; cv=none; b=SnrR9bkifgDnLIKRRItH7s4/Bsz/qEm1Oh5nO8WiPPuxhIKJn+Lz04z1HBFbkHrultaDhTljXxuM7KceSq+mNvjInS8lK8EMNNzSV61S5TzhETWkm4yV926W//k0MiZpeq+JwwX8Jmoopraxn3hb+zcJxu6ofm0QEVjTh6qOoTA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784085016; c=relaxed/simple; bh=nD/7BLwhckJ2VrbOKHww4GOUnGL9WSDMxtLvVNd99/c=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FadhbZdUJfW0dV815mjBIfdeFXkZaMeVFhYylYKSfrNnifzVDMWVqaAELtidfMGhRpzebxlj50jEZKoSVxxnoR5yj5g7bSqQOZNUxooTntLP8++MaPbfc6A1RCkM9XlZKDBn2V1vWr8LLXrXkVPdwxGZZzfHY4+J0AfEBTflYCA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EMMF0rtj; 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="EMMF0rtj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C9AAE1F00A3A; Wed, 15 Jul 2026 03:10:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784085014; bh=OZlM1xLtscWm6r5E9re97Un+lNNnhMeBCpTniJTuHyU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=EMMF0rtjKzOj0NNvQBnEZPkh8CNIg1ZQIhxvDGhbBTy52EkzBm+3e/8x2Gnzj6Nsf 6JdD3stcnyBiFwEMkFGMjBoB8/1rpHvUZEJIp8GfgSDkdu5qbhFDbhc1rFv6FIDUdb I0oASfLvYVVqGqRlhbySFBlqa/S6A2xwZtSa6v3RHhl7Z5R/2OkdsSuCpphyhzhK5A oZMVmL7hEPWSPhDuJInt53pgNVmyltHbjgSiDItpav0q/hMrlqnE4f0tjzEmPrIPp4 THGzI+Km+xtK61uFANf0yvaKZxb+YJpaqcz4xaUzCegDhRuAzJfyxmTiN76AGEoGiK I5wFy6TESpYIQ== From: SJ Park To: Andrew Morton Cc: SJ Park , stable@vger.kernel.org, Quanmin Yan , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v1.1 5/6] mm/damon/sysfs: read addr_unit only once in damon_sysfs_apply_inputs() Date: Tue, 14 Jul 2026 20:10:00 -0700 Message-ID: <20260715031002.108504-6-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260715031002.108504-1-sj@kernel.org> References: <20260715031002.108504-1-sj@kernel.org> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit damon_sysfs_apply_inputs() reads addr_unit twice. It could race with addr_unit_store(). As a result, the min_region_sz could wrongly be set up. Read it once. The user impact is trivial. Sane users ain't update the parameter in parallel. Even if it happens, the DAMON core layer handles the wrong min_region_sz (!is_power_of_2()). Even if somehow the race ended up making a min_region_sz that is different from the user's intention but still valid, only monitoring itself runs differently than expected. No critical consequences like kernel panic or memory corruption happen. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260714142950.100711-1-sj@kernel.org Fixes: 540a2aebc657 ("mm/damon/sysfs: implement addr_unit file under context dir") Cc: # 6.18.x Signed-off-by: SJ Park --- mm/damon/sysfs.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c index b5fe036f78015..65a502c7746c0 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -2099,11 +2099,11 @@ static int damon_sysfs_apply_inputs(struct damon_ctx *ctx, err = damon_select_ops(ctx, sys_ctx->ops_id); if (err) return err; - ctx->addr_unit = sys_ctx->addr_unit; + ctx->addr_unit = READ_ONCE(sys_ctx->addr_unit); /* addr_unit is respected by only DAMON_OPS_PADDR */ if (sys_ctx->ops_id == DAMON_OPS_PADDR) ctx->min_region_sz = max( - DAMON_MIN_REGION_SZ / sys_ctx->addr_unit, 1); + DAMON_MIN_REGION_SZ / ctx->addr_unit, 1); ctx->pause = sys_ctx->pause; err = damon_sysfs_set_attrs(ctx, sys_ctx->attrs); if (err) -- 2.47.3