From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta1.migadu.com (out-177.mta1.migadu.com [95.215.58.177]) (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 606281448D5 for ; Thu, 25 Dec 2025 00:29:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766622565; cv=none; b=XXRUt3Kccvegcgo8WzYFb23hqVbhQ1B50z3SfHSTAwgGWd6u8LTCUAfL+hlZ5THNoUirMNq0G8ms9Fl+tqgxhgogAVizko7XEZpNWReJoc8mvyqfZw74IgYb9BhrNcdYL8Rinl+BySlJvWUuA2HBPhrH2F0bQf90KpZ3FjaXZ1k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766622565; c=relaxed/simple; bh=4FQytIhVIzXZMikPaItf/j18QYRslFIgfG3U7DUBtho=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Grz2K5pZ9B+eqhJI7AyukTzYNLiKyJ6qCwpHN9OVx22N3kbc/QiWH4m4AtPsLzh29ltWUEs4PlXH6FYsrx3mVKF8dJkQs8982LBl5RFDpFfl9WRr2oEgmV2nrSutvkEL2E+kBUk6zNZM/nA/0mkN1HuVDuNd0oWIq77uEN6v97k= 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=95.215.58.177 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: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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( rcu_read_lock(); memcg = mem_cgroup_from_id(goal->memcg_id); - rcu_read_unlock(); - if (!memcg) { + if (!memcg || !mem_cgroup_tryget(memcg)) { + rcu_read_unlock(); if (goal->metric == 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 = mem_cgroup_lruvec(memcg, NODE_DATA(goal->nid)); used_pages = lruvec_page_state(lruvec, NR_ACTIVE_ANON); @@ -2065,6 +2067,8 @@ static unsigned long damos_get_node_memcg_used_bp( used_pages += lruvec_page_state(lruvec, NR_ACTIVE_FILE); used_pages += lruvec_page_state(lruvec, NR_INACTIVE_FILE); + mem_cgroup_put(memcg); + si_meminfo_node(&i, goal->nid); if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) numerator = used_pages; -- 2.47.3