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b=h8VgSOXe4RBqqrmytkAtjUaYqpFZB31iG18EYsKuzTkeYHceZmdu1gDbB9HrOqDlJ uFvavOa8tcq5OzbHDrc5SnPNB5Q/MWDsCtjjDliUFCs6f9dtytrKzPMHJXp/jj9Vaw G/Y9OjeXbYQ6DKa82i2CCcwLx+79TmTO1D+d1bdOn605DffZKS/Y1jvfqkJm2D0PiN i0XHJXfBg5bR8fDO6CnT0FCgMVNTeieOiZnYpQBS9FFylEFTIZMtO/Wvgq6GnQMxWi PSDa0eKT3ycmB/EGiQ9Mwl/i8y6Yd8yl+ugUEoNDnwvPsAZegiIULIwVcS3jBheejI l9fUoogPcOIkQ== From: SJ Park To: Donggeun Yoo Cc: SJ Park , akpm@linux-foundation.org, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v4 1/2] mm/damon/core: prevent size quota overflow in the temporal goal tuner Date: Tue, 22 Sep 2026 22:59:38 -0700 Message-ID: <20260923055939.3495-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260923002600.1825448-2-donggeunyoo.kernel@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: ygsjimgismaftw4antwy4cnh6xmmt75s X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 3E96F4000A X-HE-Tag: 1790143184-970173 X-HE-Meta: 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 WNNwCJnL byrrbueA8iITrVvmXbVGE0N3xbUEf2O3RHbmdBE28kuyTRPx4eNfkYe/BEV0IS2NgaoQyEmX9STE82zwOdcoVXkY/pvfZFSF2M+paXTynQcM+kEBnCLPNa+yi/0Kbq+0pW6zvB36vlkCdSaVYDnLJZUtrVaBWHK2tt9VlhYOdfAiNJ9wR7mBgclmo3hXFNKEBoJxmSQ42kPZGid8uoVxrux+kLSC1KvP2yzke03Uo7uJEJoYIPRgdSpFV8UANFl1st4JZGohrLH5L29eam4OnL/WYjRxcDeAKjK+ury7W6S3kPgVhb+rONkZ6FJwLF8YnyxxNycI/kyIgAAU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 23 Sep 2026 09:25:58 +0900 Donggeun Yoo wrote: > damos_goal_tune_esz_bp_temporal() converts the scheme's size quota > into basis points with "quota->esz_bp = quota->sz * 10000", both > unsigned long, and damos_set_effective_quota() divides the result > back by 10000. quotas/bytes is unbounded; bytes_store() hands it to > kstrtoul() as is. > > On 32-bit the product wraps for any size quota above ULONG_MAX / > 10000, that is 429496 bytes. A wrapped product below 10000 divides > to a zero effective quota: 429497 gives 0. damos_quota_is_full() is > then true on the first test of every charge window. Other wrapped > values are wrong without being zero: 500000 gives 70503. > > Triggering this needs a scheme with a quota goal, the temporal goal > tuner, and a size quota above ULONG_MAX / 10000 -- 429496 bytes on > 32-bit, 1844674407370955 on 64-bit. The scheme then makes no > progress for as long as the goal is unachieved, which is easy to > notice, and writing a smaller size quota restores it. Nothing is > corrupted and nothing leaks. This is unlikely to be hit on a tested > setup. > > addr_unit does not cover this. It only scales the numbers a paddr > context writes to quotas/bytes, so a large enough scaled value wraps > just the same, and vaddr and fvaddr contexts take raw byte values. > > Bound the multiply. Looks good to me, thank you for finding and fixing this! > > Fixes: af738a6a00c1 ("mm/damon/core: introduce DAMOS_QUOTA_GOAL_TUNER_TEMPORAL") > Cc: # 7.1.x > Signed-off-by: Donggeun Yoo Reviewed-by: SJ Park Thanks, SJ [...]