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 C9DC1368293; Sun, 12 Jul 2026 17:03:41 +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=1783875823; cv=none; b=nwMFDvPrbQFQ1wZrqq7E/OEiGaU9/1+fIezlSGLH2I/T6fT5pJZ3MWrWgUTdvQpPVSVP8lA3dc3chg9T28DA+GpxpjS8D3jCVSd4obTEwQF2nbxkTRtpldmzNmC4o42ZvhfDmzd91OQoskqkWgyZDb8ESjmk6KPqbf07D07b6rI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783875823; c=relaxed/simple; bh=nt1m4yOHpUkfhmuPI5sfQNBML1ejUt2LDcM7VHyWuzk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GtN5cBFsbZRgCVAbMjHx/zwPSYJ6HPt+V/Y3RrEyyZlYLM5adzGq0qiHmSkN6HAWQHFB67w7Mh1uxO2KmtpHGByFnCcTUk1ZO6qtnJelEHuwX2HtaF2tgQ1Co0xNlQygvipvy66y8R+8IPP187rkIsCg80im9XGaBLLYY6buFKQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jqnAdXsz; 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="jqnAdXsz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 53A4D1F00A3D; Sun, 12 Jul 2026 17:03:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783875821; bh=hhmDCI+ot7IL3VsT3pLzYBJmbk4njLZd345nGTc/fNs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=jqnAdXszxWlkiGPhG+kdzDqhjT1jdYqU0Tnu/kSJ3AMyLxt5ZpLy6QMxsZmv3a5np N8uVClMafeRShHx+Rw7BP9jddNRBrX9cBzjseNGnUi/MihUGK3Ybddi98rHiCHQXjb geQFfvghXDWU/d4XOctmwpMMxEhwPMmJ7cRocPSE64rgpaUdzqbfxeECokC1ZlazMQ bqpm69Gpg0v4AhyX/xxiJ9RNhhppw32Fb+lEvftBArHE3Xi5Hoys88Q/1gnahxHqE6 xv2Yv81igcLUYxhiVAlzno6vOk+XCuzG9SNEw6NqV/wGiKiNXkWhQ/CeYPCjPFwavb 4rA9AUj3dsOVQ== From: SJ Park To: Cc: SJ Park , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH v1.1 5/5] mm/damon/sysfs: read ops_id only once Date: Sun, 12 Jul 2026 10:03:27 -0700 Message-ID: <20260712170328.91144-6-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260712170328.91144-1-sj@kernel.org> References: <20260712170328.91144-1-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