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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: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: cm3k7w7ehk4t5au8fonyb8q7t8b779et X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4162B4000E X-Rspam-User: X-HE-Tag: 1697822345-998474 X-HE-Meta: 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 u+NZ1oAv x7T2YQN/sAPMBjjmPsC+4HO6t4oSrKfUjoFA+yPeoJbzWxUmYRBZIlMLkG1aDrKgL3YQBeZi9e5mM/fhymgm6O05iZq9QkctJLBSmWglNCF/CHyqAgawSDX10qsyP69dSoZAHUqU2Csi/BhdNAzy3SueBoyt33DsJu/TOnklaVN3CnGqK9IQdHWd4QCiETtFLDjkK1QlBHUFKb8gHfoQA9yZNxkWO88thmAgZsIzLfq5+CLEwQ0tfVun7MiP8I+J6gJBrMAiMf7288YJFwf38LVmVbEBjsEwmr8c4 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 > >