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b=gtTWEkq68BRCPoTIMh/xO2jcf7f4SPpTFGWwXwq3E+wsK122kGaF8zXok9jR/4ZwW 8jXUegn9aA4my0YZKQ+VoLwvuP1ySGFzRlsL8J/ySPK+lzgeHn7mgyVbnJDY/uq3vh ALqs+4RkE0tlxu4sirGRTyN324EqcvRY3rZoGoZGFSAzSBqX2wi0/64q50XKiX1azK Z3Y26TYLpi60/C9QUi2isC42QrXulVGNLUtcuMbSvW3A3zJqGEkNZOCDSNDdN53i63 1L2CLZBqaO4H9ECs5Gyh+6rBXisrCM69tNZyEIBz6Jk2RLN4FfyP9xgrx5prhIcnEz uazf+MjPeZO9Q== From: SJ Park To: sashiko-bot@kernel.org Cc: SJ Park , "Andrew Morton" , damon@lists.linux.dev, linux-mm@kvack.org Subject: Re: [RFC PATCH 6.18.y] mm/damon/core: error damos_commit_quota_goal() for zero target_value Date: Sun, 25 Oct 2026 10:41:37 -0700 Message-ID: <20261025174138.165096-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C02BA80006 X-Spam-Status: No, score=-14.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: t81pehjfjnc14ww18yjg8ppy89xc5idm X-HE-Tag: 1792950106-489287 X-HE-Meta: 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 IrHoWf5I Y64vn2P7aLjMoJyNepxO7GBoj3HuDe4yb1A3Imh2YY0gl1eMFFacV6tCPNaLZ9pPfl6G2rkqptbBflUEFxAGCUqTFHEINOeUNTsJkQQ45OCMDUcMMKQ4OxyytdtzWJKhFEo3jEUdqiOO53ZhVtOPZao9kxGLe7JrVD3vLfTtG1Aokf4sC7Fb2LGBVyJKK9Ulqz+KpB/OIiXBamjIQRRUIe/8+LwmGp+KZzUdKzYa6VLHH+Zqp58RADyLdSVdP8zz4Tny4JIxKP/+EPBGc3kg8X3iKL9DtSzcysT/Y3BEyKBEm7Dl/UGdO0yOCZXVrAELozNbHzFwQuK85G2eM/nn3F2JpyS/HLCRtD7ViEIrHEStaj9yq5Am5GbUgMA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Sun, 25 Oct 2026 17:37:55 +0000 sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: > - [High] mm/damon: incomplete zero target_value check in damos_commit_quota_goal() > -- > > commit ea716ea29282ef733822096401c5c8d92eaaef58 > Author: SJ Park > > mm/damon/core: error damos_commit_quota_goal() for zero target_value > > This commit validates that a DAMOS quota goal's target_value is non-zero in > damos_commit_quota_goal(), returning -EINVAL and propagating the error through > damos_commit_quota_goals() to prevent a division-by-zero in > damos_quota_score(). > > Link: https://lore.kernel.org/20260903010722.94244-1-sj@kernel.org > Link: https://lore.kernel.org/20260903010722.94244-2-sj@kernel.org > Link: https://lore.kernel.org/20260803134034.15217-1-sj@kernel.org [1] > > > diff --git a/mm/damon/core.c b/mm/damon/core.c > > index 4e6e3d7d0a5c0..8fa788b0d709c 100644 > > --- a/mm/damon/core.c > > +++ b/mm/damon/core.c > > @@ -807,15 +807,18 @@ static void damos_commit_quota_goal_union( > > } > > } > > > > -static void damos_commit_quota_goal( > > +static int damos_commit_quota_goal( > > struct damos_quota_goal *dst, struct damos_quota_goal *src) > > { > > + if (!src->target_value) > > + return -EINVAL; > > [Severity: High] > Does checking for a zero target_value only in damos_commit_quota_goal() cover > the path where DAMON is started via sysfs in this stable tree? > > In mm/damon/sysfs-schemes.c, target_value_store() updates goal->target_value > without holding damon_sysfs_lock: > > mm/damon/sysfs-schemes.c:target_value_store() { > struct damos_sysfs_quota_goal *goal = container_of(kobj, struct > damos_sysfs_quota_goal, kobj); > int err = kstrtoul(buf, 0, &goal->target_value); > > return err ? err : count; > } > > Meanwhile, damos_sysfs_add_quota_score() reads sysfs_goal->target_value twice > without synchronization against target_value_store(): > > mm/damon/sysfs-schemes.c:damos_sysfs_add_quota_score() { > if (!sysfs_goal->target_value) > continue; > > goal = damos_new_quota_goal(sysfs_goal->metric, > sysfs_goal->target_value); > ... > damos_add_quota_goal(quota, goal); > } > > If target_value_store() writes 0 between those two reads, > damos_new_quota_goal() allocates a goal with target_value == 0 and attaches it > to quota->goals. > > When starting DAMON via state_store() -> damon_sysfs_cmd_request_callback() -> > damon_sysfs_handle_cmd() -> damon_sysfs_turn_damon_on(), this branch builds > the context and starts kdamond directly without calling damon_commit_ctx() or > damos_commit_quota_goals(): > > mm/damon/sysfs.c:damon_sysfs_turn_damon_on() { > ctx = damon_sysfs_build_ctx(kdamond->contexts->contexts_arr[0]); > if (IS_ERR(ctx)) { > kfree(repeat_call_control); > return PTR_ERR(ctx); > } > err = damon_start(&ctx, 1, false); > } > > Here damon_sysfs_build_ctx() populates scheme->quota.goals via > damon_sysfs_apply_inputs() -> damon_sysfs_add_schemes() -> > damon_sysfs_mk_scheme() -> damos_sysfs_add_quota_score(), bypassing > damos_commit_quota_goal() entirely. > > When kdamond subsequently runs kdamond_fn() -> kdamond_apply_schemes() -> > damos_adjust_quota() -> damos_set_effective_quota() -> damos_quota_score(): > > mm/damon/core.c:damos_quota_score() { > highest_score = max(highest_score, > goal->current_value * 10000 / > goal->target_value); > } > > can this still divide by zero if the race occurs during > damon_sysfs_turn_damon_on()? Nice catch. I also just found this issue while working on 6.8. Same issue in the patch for 7.2.y [1]. I will withdraw this and that, and work on the next spin. [1] https://lore.kernel.org/20261025172434.161597-1-sj@kernel.org > > -- > Sashiko AI review ยท https://sashiko.dev/#/patchset/20261025172712.164385-1-sj@kernel.org?part=1 Thanks, SJ