From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C5F6C433FE for ; Mon, 18 Oct 2021 09:02:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 583256127B for ; Mon, 18 Oct 2021 09:02:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231248AbhJRJE4 (ORCPT ); Mon, 18 Oct 2021 05:04:56 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:60781 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231149AbhJRJEz (ORCPT ); Mon, 18 Oct 2021 05:04:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1634547763; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=fhNdqsd01Iuu4MdS4LMgpHQ2OS3OKZxf9FLM+N5TUbc=; b=Pd7RAEz1rk4n9OhQ7OFOm8EVMfDpmBcSKKAUdyZ8Fltj4TfeiUcZKyKaqdAtLAFTpMB93B 7p2bFcxZsMfc0rvibe+uwryErcj78i15v3pBVaJ6sjO8c00MdI0sUctv1OiowZeBArVL1Z EF714FAGcbReaeVS/tDaaKGFXCQuVtI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-582-MFUBO455MQKwhMLo8RLrDg-1; Mon, 18 Oct 2021 05:02:40 -0400 X-MC-Unique: MFUBO455MQKwhMLo8RLrDg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D3DB218125C2; Mon, 18 Oct 2021 09:02:37 +0000 (UTC) Received: from T590 (ovpn-8-37.pek2.redhat.com [10.72.8.37]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 16265196E5; Mon, 18 Oct 2021 09:02:23 +0000 (UTC) Date: Mon, 18 Oct 2021 17:02:18 +0800 From: Ming Lei To: quanyang.wang@windriver.com Cc: Tejun Heo , Zefan Li , Johannes Weiner , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Jens Axboe , Roman Gushchin , mkoutny@suse.com, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [V2][PATCH] cgroup: fix memory leak caused by missing cgroup_bpf_offline Message-ID: References: <20211018075623.26884-1-quanyang.wang@windriver.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211018075623.26884-1-quanyang.wang@windriver.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Oct 18, 2021 at 03:56:23PM +0800, quanyang.wang@windriver.com wrote: > From: Quanyang Wang > > When enabling CONFIG_CGROUP_BPF, kmemleak can be observed by running > the command as below: > > $mount -t cgroup -o none,name=foo cgroup cgroup/ > $umount cgroup/ > > unreferenced object 0xc3585c40 (size 64): > comm "mount", pid 425, jiffies 4294959825 (age 31.990s) > hex dump (first 32 bytes): > 01 00 00 80 84 8c 28 c0 00 00 00 00 00 00 00 00 ......(......... > 00 00 00 00 00 00 00 00 6c 43 a0 c3 00 00 00 00 ........lC...... > backtrace: > [] cgroup_bpf_inherit+0x44/0x24c > [<1f03679c>] cgroup_setup_root+0x174/0x37c > [] cgroup1_get_tree+0x2c0/0x4a0 > [] vfs_get_tree+0x24/0x108 > [] path_mount+0x384/0x988 > [] do_mount+0x64/0x9c > [<208c9cfe>] sys_mount+0xfc/0x1f4 > [<06dd06e0>] ret_fast_syscall+0x0/0x48 > [] 0xbeb4daa8 > > This is because that since the commit 2b0d3d3e4fcf ("percpu_ref: reduce > memory footprint of percpu_ref in fast path") root_cgrp->bpf.refcnt.data > is allocated by the function percpu_ref_init in cgroup_bpf_inherit which > is called by cgroup_setup_root when mounting, but not freed along with > root_cgrp when umounting. Adding cgroup_bpf_offline which calls > percpu_ref_kill to cgroup_kill_sb can free root_cgrp->bpf.refcnt.data in > umount path. > > This patch also fixes the commit 4bfc0bb2c60e ("bpf: decouple the lifetime > of cgroup_bpf from cgroup itself"). A cgroup_bpf_offline is needed to do a > cleanup that frees the resources which are allocated by cgroup_bpf_inherit > in cgroup_setup_root. > > And inside cgroup_bpf_offline, cgroup_get() is at the beginning and > cgroup_put is at the end of cgroup_bpf_release which is called by > cgroup_bpf_offline. So cgroup_bpf_offline can keep the balance of > cgroup's refcount. > > Fixes: 2b0d3d3e4fcf ("percpu_ref: reduce memory footprint of percpu_ref in fast path") If I understand correctly, cgroup_bpf_release() won't be called without your patch. So anything allocated in cgroup_bpf_inherit() will be leaked? If that is true, 'Fixes: 2b0d3d3e4fcf' looks misleading, cause people has to backport your patch if 4bfc0bb2c60e is applied. Meantime, this fix isn't needed if 4bfc0bb2c60e isn't merged. Thanks, Ming