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[23.116.43.216]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7c7f54c29ddsm48585327b3.34.2026.05.16.14.04.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 16 May 2026 14:04:03 -0700 (PDT) From: Ravi Jonnalagadda To: sj@kernel.org, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Cc: akpm@linux-foundation.org, corbet@lwn.net, bijan311@gmail.com, ajayjoshi@micron.com, honggyu.kim@sk.com, yunjeong.mun@sk.com, ravis.opensrc@gmail.com Subject: [RFC PATCH 1/5] mm/damon/core: fix nr_accesses_bp underflow in damon_moving_sum Date: Sat, 16 May 2026 14:03:53 -0700 Message-ID: <20260516210357.2247-2-ravis.opensrc@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260516210357.2247-1-ravis.opensrc@gmail.com> References: <20260516210357.2247-1-ravis.opensrc@gmail.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Guard against unsigned integer underflow when nomvsum/len_window exceeds mvsum. When that subtraction wraps, the moving sum returns a near-ULONG_MAX value and corrupts nr_accesses_bp. If subtrahend > mvsum, return new_value: this clamps the moving-sum estimate to the current observation rather than wrapping. Signed-off-by: Ravi Jonnalagadda --- mm/damon/core.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 3a8725e400c6b..9975f3d9ebfe9 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -3449,7 +3449,11 @@ int damon_set_region_system_rams_default(struct damon_target *t, static unsigned int damon_moving_sum(unsigned int mvsum, unsigned int nomvsum, unsigned int len_window, unsigned int new_value) { - return mvsum - nomvsum / len_window + new_value; + unsigned int subtrahend = nomvsum / len_window; + + if (subtrahend > mvsum) + return new_value; + return mvsum - subtrahend + new_value; } /** -- 2.43.0