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b=RHa0UaAVPETqYGAj1f2w9QCVcoQ0v3iwH8D7S44GHnF2xZzYLokpnnGdE7u6HbC4u ASd2gfW2bVw2bQz19NKhIyZaMXoRVY0rE60pmarGHG97qkNfw+l58B6KaJm4Qg4d01 kGN8DTxgm+y6FOEkBW+r36X9oKyNo7I0Bp4Men2vD1s3T5hBIA7FHicepRpHEKWlLn gaPB0T6fCi4a9vfB5F2onDPJfvg7kFGrFvRaZX4IB7c8YfPNfqONlKmUHLaqBZ/dCo FooHO1Ob0de/jvzGr/49NyJy15U6ieMa7onZ4Fuf3yNtQQM46HWSnJkmsZtaL+cHzz 6q/pg89fzn3PQ== From: SeongJae Park To: Cc: SeongJae Park , "# 5 . 16 . x" , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH v1.2 1/2] mm/damon/core: handle zero intervals in damon_max_nr_accesses() Date: Mon, 22 Jun 2026 07:10:24 -0700 Message-ID: <20260622141027.29145-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260622141027.29145-1-sj@kernel.org> References: <20260622141027.29145-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: ED16940002 X-Rspam-User: X-Stat-Signature: 78s5achescfcyi4w4g38fnskzfqq7tgo X-HE-Tag: 1782137442-589952 X-HE-Meta: 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 rDHiKdZ0 DE4JUpK9rx0y6aSlLax9AdPEwc5kaCJoTBSpOf0TMqKSk+xsBxU+3cbQsXlyXIHNyFT1Jd2MX0VLt7nGSlXRxzEv7mH/6mTc4W4T94ZVsDTCGSmHNuEJQsTICiOd3W16en0iXInNoCJryqkvUjim26FeCDQzZHnQ0PWywEw/EiK9KVGdv16KbgHqS5konWbjzOUBF+Lv/ODmY+ShL6Hqw/E5r6ve3EtyHHzMR8qQoJ2aVY1BuM/P70dOT5QVCFsDoZ49sOQn2Sg4NYbjLyTE0I/O5Qg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: damon_max_nr_accesses() causes a divide-by-zero if the sampling interval is set to zero by the user. If the aggregation interval is set to zero, the function returns zero. It is wrong, since the real maximum nr_acceses in the setup should be one. Worse yet, it can cause another divide-by-zero from its caller, damon_hot_score(), since it uses damon_max_nr_accesses() return value as a denominator. Fix the problem by setting the denominator in the function as 1 when the sampling interval is zero. Also ensure the return value is always 1 or greater. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260619202459.145010-1-sj@kernel.org Fixes: 198f0f4c58b9 ("mm/damon/vaddr,paddr: support pageout prioritization") Cc: # 5.16.x Signed-off-by: SeongJae Park --- include/linux/damon.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/include/linux/damon.h b/include/linux/damon.h index 64d75c78f4df4..02ac34537df9a 100644 --- a/include/linux/damon.h +++ b/include/linux/damon.h @@ -1066,9 +1066,13 @@ static inline bool damon_target_has_pid(const struct damon_ctx *ctx) static inline unsigned int damon_max_nr_accesses(const struct damon_attrs *attrs) { - /* {aggr,sample}_interval are unsigned long, hence could overflow */ - return min(attrs->aggr_interval / attrs->sample_interval, + unsigned long sample_interval; + unsigned long max_nr_accesses; + + sample_interval = attrs->sample_interval ? : 1; + max_nr_accesses = min(attrs->aggr_interval / sample_interval, (unsigned long)UINT_MAX); + return max_nr_accesses ? : 1; } -- 2.47.3