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b=E1VkfEE73Ld52yTp8XyAQnrJXqTiZfuPBrpHJg+wQgO+3sNQ0Iyu8PFiSyJKuDbfW 3LWPnW+dMyu7SVgLfgHiFoaZGVFY8xNd8VJu2HvUcIds2AT64Af4X2wpvGjjAIlYWr CLrl4T0i7m2CYniO15KQb6ZXzke4uxN7QXT/oY2PnJYdnfys+nwsgv85juPh4Gh1Dl ZGuVYrxhMsoNjjfaeFcQpFodyLIDvCoIsJDoyIgBeDLnLsDS68WGxSyzPhsTDCixx5 BFb0yKZ04XxR4H3Ii52aoGoEW7pZF983iz5p3Rmu7pdCgZ9Fi8s6OdJ93u6AalQbzP r6ZQ95HO5A2CA== From: SJ Park To: Cc: SJ Park , stable@vger.kernel.org, Andrew Morton , Brendan Higgins , David Gow , damon@lists.linux.dev, kunit-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH v1.1 1/7] mm/damon/core: initialize damos->last_applied Date: Fri, 17 Jul 2026 07:34:38 -0700 Message-ID: <20260717143445.91207-2-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260717143445.91207-1-sj@kernel.org> References: <20260717143445.91207-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: 1i938bkysi4hao647t6uhn1kguub57ws X-Rspamd-Queue-Id: 588E140003 X-Rspamd-Server: rspam01 X-Rspam-User: X-HE-Tag: 1784298895-122314 X-HE-Meta: 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 Jo3I/oXH 6vXbABVIcCS3Jk4JjguWyePsN8hVJBRCoDXEk50iTEprgo66op3N5mHov4PON1+XxKvp6Fko1Dp6f+cK1tyvOBlxDcCCoh80fP0tHIAGtLXTzz0iynmNFYRodYukmxHoWapUBA4JQRMovz896yN8mYyNQBA+JJWLr8d8w4iu6mlOBt1dRdvU2cHE768XAZcUvQuR3rriz1eLh72WBFQlqFIfsIlGwoXw+c5snOO2vbyUrfTnR3jW4cEDyI/0vP38Jll6GrFwHO+KGkG1U9e6VRPhstZIDryD/Wlkv Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Multiple DAMON regions could exist across a folio. If they fulfill the condition to apply a DAMOS scheme, the scheme could be applied multiple times to the folio. To avoid this, each DAMOS scheme stores the folio that the scheme was applied to last time in the damos->last_applied field and skips repeatedly applying the same scheme to the same folio. The field is being used without initialization, though. Hence, the mechanism could wrongly skip applying a scheme to a folio at the very first time of DAMOS run. The user impact is trivial. DAMON might unexpectedly skip applying DAMOS action for one folio for the first time per scheme. In the DAMON's best-effort world, this is never a real problem. No critical consequences such as kernel panic or memory corruption happen. It is a clear bug, though, and the fix is straightforward. Fix the issue by initializing the field in DAMOS scheme creation function, damon_new_scheme(). The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260714055436.120034-1-sj@kernel.org Fixes: 94ba17adaba0 ("mm/damon: avoid applying DAMOS action to same entity multiple times") Cc: # 6.15.x Signed-off-by: SJ Park --- mm/damon/core.c | 1 + 1 file changed, 1 insertion(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index f464b4f0976c3..60255f5cd715e 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -705,6 +705,7 @@ struct damos *damon_new_scheme(struct damos_access_pattern *pattern, INIT_LIST_HEAD(&scheme->ops_filters); scheme->stat = (struct damos_stat){}; scheme->max_nr_snapshots = 0; + scheme->last_applied = NULL; INIT_LIST_HEAD(&scheme->list); scheme->quota = *(damos_quota_init(quota)); -- 2.47.3