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b=Csa8MwEFaic9IVgL0owHD2cYFCYaWnmdqWiH8kqDGQNXjsdcKfc5hQIc4tjc6oCaW kcfCt96pW2vhxCrNJLh5pv0E55wI5wOvgh04u85WPYUPx4VvcfiXZlBFp/vx5l8Rt2 HeGhMaFnEnbdCgaq9U0bvRgnT2w6F7fw7nxYYTEx8HNq9yBINXCX52wukNlyrS90Zy 5Gv+XUAzOFlcKdE3Ye0MwEa+pSwlHT0ZD0TrQqMCUoddkq1guzcTx3wE/JldWRodQV iW4RhJ/robHJQbnlR2huvN5JE3jo3QDB2ZgczmMHiAg5POaurTj/tlVXwl+WwcmmTx L+Zju82o9ZA7g== From: SeongJae Park To: Akinobu Mita Cc: SeongJae Park , damon@lists.linux.dev, linux-mm@kvack.org, akpm@linux-foundation.org Subject: Re: [PATCH] mm/damon/core: avoid destroyed target reference from DAMOS quota Date: Sat, 17 May 2025 08:56:33 -0700 Message-Id: <20250517155633.35139-1-sj@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250517141852.142802-1-akinobu.mita@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B9230C0014 X-Stat-Signature: d47b4bmr463prwc5q9gg4x7obttfsu6x X-HE-Tag: 1747497398-454270 X-HE-Meta: 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 T+XGIyyG OdDO9nZfWrRDBOVaRhwgJeaRuP/3N7BSaTuujwVeBD3n9dO8bBW9Nu0D6kCt8v7bjy1K74mUdYuc1vtN/L4MPo3EkFeoZWYgCCoHlVeEbdDX29ZqFuR4Y51wLIzMmkI7LWdrAk+qPP3t8tOxbxjzwgckKva14CuI+OKe/Hlm/kxxxN5g625dNdGtD53IqJdsDOPXDsSyij9Kp6vD4hAfymv4Pl/Tzh9Nr8/Y7jWtxcAfmuGSk69DOBbdTECUQj1Yxk3j5MRGegDloSsjgYjkkcrzg4Z6CdehAanXixshlCDB8IVM2JG7nfL5wUKBuvSx+h7rp X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, 17 May 2025 23:18:52 +0900 Akinobu Mita wrote: > When the number of the monitoring targets in running contexts is reduced, > there may be DAMOS quotas referencing the targets that will be destroyed. > > Applying the scheme action for such DAMOS scheme will be skipped forever > looking for the starting part of the region for the destroyed monitoring > target. Nice catch! > > To fix this issue, when the monitoring target is destroyed, reset the > starting part for all DAMOS quotas that reference the target. > I think this deserves below Fixes: tag? Fixes: da87878010e5 ("mm/damon/sysfs: support online inputs update") For a clarification. The worst scenario consequence of this issue is DAMOS unexpectedly doing less or zero works under certain setups. No horrible problems such as a use after free will happen, though, since quota handling code references quota.charge_target_from, but does not de-reference it. So I don't think this deserves Cc-ing stable@, but I'll let stable@ maintainers decide, as usual. > Signed-off-by: Akinobu Mita > Cc: SeongJae Park Reviewed-by: SeongJae Park Thanks, SJ [...]