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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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 1E083A0009 X-Rspamd-Server: rspam06 X-Stat-Signature: d3df99ti8ac49etfjwnhntpadgix9fxu X-HE-Tag: 1778965444-409934 X-HE-Meta: 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 T5LVbla0 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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