From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ming Lei Subject: Re: [V2][PATCH] cgroup: fix memory leak caused by missing cgroup_bpf_offline Date: Mon, 18 Oct 2021 20:59:37 +0800 Message-ID: References: <20211018075623.26884-1-quanyang.wang@windriver.com> <8fdcaded-474e-139b-a9bc-5ab6f91fbd4f@windriver.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1634561994; 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=89JYMjE+XHB7qedkDizTkhtu+clm8RkyokklVgx90oA=; b=jCZKTx/evdydZ+PDpjcto/tGbz89ry+DmAKpAib87OpK6SfV9tgfXRPKPZlyP1jq9XV8Wk 7WONStrufCICOZt/6DUTp7dVqK+9JN1+z5R0tLyw8wAIcenjTU8nqiQtt1lFY9nlQNmJS/ HZZI30F0+YGwyWKEGVVQWEhJMV+Jedk= Content-Disposition: inline In-Reply-To: <8fdcaded-474e-139b-a9bc-5ab6f91fbd4f-CWA4WttNNZF54TAoqtyWWQ@public.gmane.org> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Quanyang Wang Cc: Tejun Heo , Zefan Li , Johannes Weiner , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Jens Axboe , Roman Gushchin , mkoutny-IBi9RG/b67k@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, bpf-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On Mon, Oct 18, 2021 at 06:06:28PM +0800, Quanyang Wang wrote: > Hi Ming, > > On 10/18/21 5:02 PM, Ming Lei wrote: > > On Mon, Oct 18, 2021 at 03:56:23PM +0800, quanyang.wang-CWA4WttNNZF54TAoqtyWWQ@public.gmane.org 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? > No, for now cgroup_bpf_release is called to release bpf.refcnt.data of the > cgroup which is not root_cgroup. Only root_cgroup's bpf data is leaked. You mean that cgroup_bpf_inherit() allocates nothing for root_cgroup? If yes, I agree you can add 'Fixes: 2b0d3d3e4fcf', otherwise please remove it. Thanks, Ming