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h=From:To:Cc:Subject:Date; b=klcEEeG5r26a752OnGHWbItqLU1kKKo46ac8VLwBGsFHh4YmfAP4a9hs3sNU1/D0W 6mrdpuhP7/fsUJRbDiyLfUw7Nd0McK5X6oSG92ohLLEwJQW0KvJE7nNA2RPxZPKKto hBXzW7FlMVEnDmZyJatR5w1zD7cuecdayNSZ+yByNCElJFzudbZq2AuUIr1DluRMFn pAdn5vGiJ1rZzu2G3WU/rT717w9D5dn4qaUYA1QVDS7R8ilTM7RhKw1K+iZrcCNDJy 6XGsDDxcvGusUf6ecl1W7tI6H4wnxf7NtAkDScQDOb9x3g5o88/TelXd3b+qt09XvQ GTDiBkfHgY/Yg== 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 v1.1] mm/damon/core: handle zero intervals in damon_max_nr_accesses() Date: Sat, 20 Jun 2026 10:14:12 -0700 Message-ID: <20260620171413.89555-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: 78ff91akn7rrofnnt3qm13h89joaw5wq X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: C784240002 X-HE-Tag: 1781975669-242336 X-HE-Meta: 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 WKO7aIUD tsP5yaCdn7m86K1MidIvuHSsvxtAq2jTVw1c7GmN8Pz6kOTBbHZnviOY9QYHtYCKGvenLNkIdd/PKs0jl50TTgD9Q/MRHkuWoh1V+J1tortT1zzuA12ufzshYlq9H/9QuAU3B2TU5lgx9prKO/5TiOTqByIYg8fmQZlQuThDNfvUMhYC68hOOdY2lX/BWiU4szQ8+XAPGe+rKnpzsRho1hR7HQo3oHvqRKXbk+AwltGci9AxA3Iu5YNfUlYaxQmHJoknaslVF/OXek+ecbf3DxPHPsA== 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 causes 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 dicovered [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 --- Changes from RFC v1 - rfc v1: https://lore.kernel.org/20260619205144.150664-1-sj@kernel.org - Handle zero aggr_interval case. 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; } base-commit: 7a58ae62cdf3c006a53b805bbb12079ab2621a07 -- 2.47.3