From nobody Sat Feb 7 17:55:24 2026 Received: from out-182.mta0.migadu.com (out-182.mta0.migadu.com [91.218.175.182]) (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 E55F427470 for ; Wed, 24 Dec 2025 03:46:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.182 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766547967; cv=none; b=lWhubmMZjMC4rNEdrSb7gZbJpMvF8Bz6qnRvTVlfjhx99bvEEv5mOhsh9jrvB0c8bJd9BR48u59mflpLq1LDUkwetnOdxsq6kQQuWI6eSy0xRArX0V4wWiMA+CAN75Sshm2k5Fqcos9DOISjX+YHOw0jTY2ngXq9AhNCnpOq/vc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766547967; c=relaxed/simple; bh=iHvGdso28WEtSoP+2m3AYidMECha6ww3ar+AohPHQpU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=l1dXrSWSPXY0Kvyyq/5u7YMscbsMZ4FWj4RXYts5j/8T8u/q1GiKH9CcL3tYAvu2MXPm/w0TKJZ2ZhguN4qLJCwUAM2pMikJxCuyhWtQdyBOFeAkeTSmRh38OvbF/wADJ6RbyZnFZ/aZ2r/xhiSmoNzb34M3tz8PTF83WcZjTGc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=lvjG7KPr; arc=none smtp.client-ip=91.218.175.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="lvjG7KPr" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1766547962; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=SypNxq4ihkSOpwufXMhOr4v6vA4rTimGBEpmyUwAS38=; b=lvjG7KPr3mKzGajh8YrxhwMJQ1a8J2HScnYZq9MVlcn/asADajOhFVEAb9UP2H6Bmk6H5X 2x7u/CdWwkIWl873VSWvPxx0RKUKhnKYDX/UxembPa88QErwNyTOmYs1kp+l08BjT30A+/ SWXYO/277sqa4GJjcRD1rR4oDyisjQQ= From: Shakeel Butt To: Andrew Morton Cc: SeongJae Park , damon@lists.linux.dev, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: [PATCH] memcg: damon: get memcg reference before access Date: Tue, 23 Dec 2025 19:45:27 -0800 Message-ID: <20251224034527.3751306-1-shakeel.butt@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" The commit b74a120bcf507 ("mm/damon/core: implement DAMOS_QUOTA_NODE_MEMCG_USED_BP") added accesses to memcg structure without getting reference to it. This is unsafe. Let's get the reference before accessing the memcg. Fixes: b74a120bcf507 ("mm/damon/core: implement DAMOS_QUOTA_NODE_MEMCG_USED= _BP") Signed-off-by: Shakeel Butt Reviewed-by: SeongJae Park --- mm/damon/core.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 4ad5f290d382..89982e0229f0 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2051,13 +2051,15 @@ static unsigned long damos_get_node_memcg_used_bp( =20 rcu_read_lock(); memcg =3D mem_cgroup_from_id(goal->memcg_id); - rcu_read_unlock(); - if (!memcg) { + if (!memcg || !mem_cgroup_tryget(memcg)) { + rcu_read_unlock(); if (goal->metric =3D=3D DAMOS_QUOTA_NODE_MEMCG_USED_BP) return 0; else /* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */ return 10000; } + rcu_read_unlock(); + mem_cgroup_flush_stats(memcg); lruvec =3D mem_cgroup_lruvec(memcg, NODE_DATA(goal->nid)); used_pages =3D lruvec_page_state(lruvec, NR_ACTIVE_ANON); @@ -2065,6 +2067,8 @@ static unsigned long damos_get_node_memcg_used_bp( used_pages +=3D lruvec_page_state(lruvec, NR_ACTIVE_FILE); used_pages +=3D lruvec_page_state(lruvec, NR_INACTIVE_FILE); =20 + mem_cgroup_put(memcg); + si_meminfo_node(&i, goal->nid); if (goal->metric =3D=3D DAMOS_QUOTA_NODE_MEMCG_USED_BP) numerator =3D used_pages; --=20 2.47.3