From mboxrd@z Thu Jan 1 00:00:00 1970 From: Quanyang Wang Subject: Re: [V2][PATCH] cgroup: fix memory leak caused by missing cgroup_bpf_offline Date: Mon, 18 Oct 2021 18:06:28 +0800 Message-ID: <8fdcaded-474e-139b-a9bc-5ab6f91fbd4f@windriver.com> References: <20211018075623.26884-1-quanyang.wang@windriver.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=windriver.com; h=subject : to : cc : references : from : message-id : date : in-reply-to : content-type : content-transfer-encoding : mime-version; s=PPS06212021; bh=e6mL/tcgbZqVrGO/gRpWCz2Ek02OFJyMV0YVhGADKC0=; b=UmIiBjWXLZ1lM4fT5OemfjBSsyP3wjy3qmyGgW6wSyvZBNbwSxExxo5XtDgTCsrEarkY N/iAS7QCA/95NJ/duJwmbf9IDEC2bRUBbCrKT9MwEKhXxM/0yi9VhaPMfsyRugW91Z3W VWlGJuR78FWRBONixmnK8BDXvBWfQWCd1rO2NTrvRvn6mB77oZ7Ipya8ly8WYCOBFPqa KDHSHaxx4lKo+2b4Eh3lCkRBJxLh2pRqppiDZrsmbV9b4LZQ/vQcvSOvnKjh43dgKu3G 191OW7JRD5+uQluEGVCrpdiQrBip67db8vAB/BmfBVwUdiflHWo8G4yTnfCeC0i4VojN 1Q== In-Reply-To: Content-Language: en-US List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Ming Lei 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 Hi Ming, On 10/18/21 5:02 PM, Ming Lei wrote: > 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? 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. For non-root cgroup: cgroup_mkdir -> cgroup_create -->cgroup_bpf_inherit(cgrp_A) cgroup_rmdir ->cgroup_destroy_locked() -->cgroup_bpf_offline(cgrp_A) So for non-root cgroup, there is no memory leak. For root cgroup: cgroup_setup_root ->cgroup_bpf_inherit(root_cgrp) cgroup_kill_sb: -> (Here should be call cgroup_bpf_offline, or else leak occurs) Thanks, Quanyang > > 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 >