From nobody Sun Feb 8 01:30:52 2026 Received: from out-181.mta1.migadu.com (out-181.mta1.migadu.com [95.215.58.181]) (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 446C01448D5 for ; Thu, 25 Dec 2025 00:29:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.181 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766622574; cv=none; b=PArjxI//3pMBYJiMRvUlhXvpVPSLMmi9k2C+GzJeb25bHjSkSpDu24+lLzzM+F31RJYtPQe+nw3T+ny5EJPvuUCTKxXPqUtoIPpGLHVhqUWNeaQZXMVHHordrj+/Fk4qCaV3/yDo2PwruSLG+wAHxd82tSEwwc4WAhVzddfwqTg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766622574; c=relaxed/simple; bh=4FQytIhVIzXZMikPaItf/j18QYRslFIgfG3U7DUBtho=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=kLOygMtecUKrSJxY7EW7kjP/fF1cdpOfV3UbrmNG4Qahxkw9/BZrwMo0M5O7R+2W9z2baKLvlCn+2l82rfWTKkXzRqHBZWq4pYeKuttYIYNPuCtJsPvqRf1HtUI5XqPo3+HujxytCKRL7C9A1YOiaqnUejNqYd1Z1fhczjZKbWA= 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=u0/s1HHP; arc=none smtp.client-ip=95.215.58.181 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="u0/s1HHP" 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=1766622560; 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=a6/TuFgHDhkQPqtZC3cXUeXixV3IdjP9zJRQmDjzS7I=; b=u0/s1HHPacfKvQQHZLVvK3I8siddC98FD4MUpujV9KIwdGqDxzF+xqMNUFlJXs+Gtbvp1y XwvgQ/kDtVyG+BNBAtdFHUVBC21vcrcWZbpjMBG9DbaIvaDCWcmuab0iX1O7s3CVDvarSG WN2LsF682W2XPgFKuH+W7pR1o7RNxbs= 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 v2] mm/damon/core: get memcg reference before access Date: Wed, 24 Dec 2025 16:29:04 -0800 Message-ID: <20251225002904.139543-1-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 --- Changes since v1: - Changed the subject as requested by SJ. 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