From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 54664200B8 for ; Fri, 20 Oct 2023 17:19:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZtO5ia0w" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 45A5FC433C7; Fri, 20 Oct 2023 17:19:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1697822343; bh=hlMCZswAeW4ccJFBbACI6PkjYN5gySJRK7nIvHrFtHo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZtO5ia0wmqJHeYNzWciWtWsLxNbHGiBlcLMyPFb6hXavXjgv5VnP4lfJ52q0tgsOd tF0Uet6ldgFGLrp5CW04DQxCFjnipDwL96aMLqx2SeFiYguJvWDwmqIAotzUwAH1BX nB6dz3poX4KLG+C2odATiZdRMdqQvBzOMXXpanjRFwA0+n+uZHArnwRMP+hf4s97NZ tuZQlKTksfR72h3efgJydVRr9aNIT3XmBt5RO9Dh3pIlawkfaUdmD0gmBDccYEPytX 6NYSI2Ski0mlHbQZBCRG/qWkvR8hqSk9TqaLoagnTPoMHCb2OqGcKzKgqd31ey7Fcm 1EAWXywmPKm+w== From: SeongJae Park To: SeongJae Park Cc: Andrew Morton , damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, acsjakub@amazon.de Subject: Re: [PATCH 0/5] avoid divide-by-zero due to max_nr_accesses overflow Date: Fri, 20 Oct 2023 17:19:01 +0000 Message-Id: <20231020171901.63994-1-sj@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231019194924.100347-1-sj@kernel.org> References: Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Thu, 19 Oct 2023 19:49:19 +0000 SeongJae Park wrote: > The maximum nr_accesses of given DAMON context can be calculated by > dividing the aggregation interval by the sampling interval. Some logics > in DAMON uses the maximum nr_accesses as a divisor. Hence, the value > shouldn't be zero. Such case is avoided since DAMON avoids setting the > agregation interval as samller than the sampling interval. However, > since nr_accesses is unsigned int while the intervals are unsigned long, > the maximum nr_accesses could be zero while casting. Actually, the issue was reported by Jakub, and I didn't add 'Reported-by:' tags for him. I sure Andrew could add that on his own, but I want to minimize Andrew's load, so will send v2 of this patchset. Andrew, please let me know if that doesn't help but only increasing your load. Thanks, SJ > > Avoid the divide-by-zero by implementing a function that handles the > corner case (first patch), and replaces the vulnerable direct max > nr_accesses calculations (remaining patches). > > Note that the patches for the replacements are divided for broken > commits, to make backporting on required tres easier. Especially, the > last patch is for a patch that not yet merged into the mainline but in > mm tree. > > SeongJae Park (5): > mm/damon: implement a function for max nr_accesses safe calculation > mm/damon/core: avoid divide-by-zero during monitoring results update > mm/damon/ops-common: avoid divide-by-zero during region hotness > calculation > mm/damon/lru_sort: avoid divide-by-zero in hot threshold calculation > mm/damon/core: avoid divide-by-zero from pseudo-moving window length > calculation > > include/linux/damon.h | 7 +++++++ > mm/damon/core.c | 12 +++--------- > mm/damon/lru_sort.c | 4 +--- > mm/damon/ops-common.c | 5 ++--- > 4 files changed, 13 insertions(+), 15 deletions(-) > > > base-commit: e845524c56a529768a8793e96304db09134eafdf > -- > 2.34.1 > >