From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7637347AF65; Tue, 14 Jul 2026 13:52:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784037163; cv=none; b=JBHb7+2smFW53LxwW0Wl/+EY3boIiHA7zIL22dYsy1iENVaYUlP2uOiWP/jy1KpQkmtyEwSmrVk7UR7j3T5Jd0jr/e577ffKWTUnqz/4hEy7A3+HmC+VkATtU/gVNeuiESu3AnSM2v1LIgwFhdtPf2kETTsG1JASQHoMj4pjfZA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784037163; c=relaxed/simple; bh=nt1m4yOHpUkfhmuPI5sfQNBML1ejUt2LDcM7VHyWuzk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=qISd9r+J7m2jx+cWyx95SVgNnxeFErvMreP/8QKee1n1UG4h+1oIFHxl3ruV8zcJZwklZKRiYP2IuUlnMvTeMdqJCBC6+ISzdRziFyeuIQtb19GfqI0DD+OnmWHLtIphzOsDeBJNTNlciX3d1wu6BbGW1tugesgwaDRXTxKRtCY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=d0KLQDgD; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="d0KLQDgD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 374B31F00A3F; Tue, 14 Jul 2026 13:52:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784037162; bh=hhmDCI+ot7IL3VsT3pLzYBJmbk4njLZd345nGTc/fNs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=d0KLQDgDpLeerstVYPZQr9U6UvUxQHOZeA3gGp96M0sHUHYIQvTLsOQu8j9ZkZjOD Lovnt/dNpVbutyl7O51WD5VJYBEOgKrYFJjtMEoncELZe33ehRqbD+sSZiWgKYb4m2 wP5jZhnfLWN9umI+1wMHvD58d0IzCHJfg9r+nPLg2wTwZrhkecb7VwubPiq22IzErr YAjwXNS1SmHclM456MNnuIKt8whSfSxja5+wfsMKqTzdQ6vqfb+pxXQ7/MXaNzlIOT MUZUt7TAAI3Yos/2cya6zodYFjT0hf0O8Hr8wPKBDsmv9Q6RL6Q1YygDFB+cld3LSr XAASuxfuqLPhg== From: SJ Park To: Andrew Morton Cc: SJ Park , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 5/5] mm/damon/sysfs: read ops_id only once Date: Tue, 14 Jul 2026 06:52:33 -0700 Message-ID: <20260714135236.92699-6-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260714135236.92699-1-sj@kernel.org> References: <20260714135236.92699-1-sj@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit damon_sysfs_apply_inputs() reads ops_id twice. It could race with ops_id_store(). As a result, the min_region_sz could wrongly be set up. Read it once. The user impact is trivial. Sane users ain't update the parameter in parallel. Even if it happens, only monitoring itself runs differently than expected. No critical consequences like kernel panic or memory corruption happen. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260703172417.95426-1-sj@kernel.org Signed-off-by: SJ Park --- mm/damon/sysfs.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c index b5fe036f78015..60a1a9e4ada34 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -2094,14 +2094,16 @@ static inline bool damon_sysfs_kdamond_running( static int damon_sysfs_apply_inputs(struct damon_ctx *ctx, struct damon_sysfs_context *sys_ctx) { + enum damon_ops_id ops_id; int err; - err = damon_select_ops(ctx, sys_ctx->ops_id); + ops_id = READ_ONCE(sys_ctx->ops_id); + err = damon_select_ops(ctx, ops_id); if (err) return err; ctx->addr_unit = sys_ctx->addr_unit; /* addr_unit is respected by only DAMON_OPS_PADDR */ - if (sys_ctx->ops_id == DAMON_OPS_PADDR) + if (ops_id == DAMON_OPS_PADDR) ctx->min_region_sz = max( DAMON_MIN_REGION_SZ / sys_ctx->addr_unit, 1); ctx->pause = sys_ctx->pause; -- 2.47.3