From: Quanyang Wang <quanyang.wang@windriver.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>, Jens Axboe <axboe@kernel.dk>,
Roman Gushchin <guro@fb.com>,
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
Date: Mon, 18 Oct 2021 18:06:28 +0800 [thread overview]
Message-ID: <8fdcaded-474e-139b-a9bc-5ab6f91fbd4f@windriver.com> (raw)
In-Reply-To: <YW04Gqqm3lDisRTc@T590>
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 <quanyang.wang@windriver.com>
>>
>> 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:
>> [<e95a2f9e>] cgroup_bpf_inherit+0x44/0x24c
>> [<1f03679c>] cgroup_setup_root+0x174/0x37c
>> [<ed4b0ac5>] cgroup1_get_tree+0x2c0/0x4a0
>> [<f85b12fd>] vfs_get_tree+0x24/0x108
>> [<f55aec5c>] path_mount+0x384/0x988
>> [<e2d5e9cd>] do_mount+0x64/0x9c
>> [<208c9cfe>] sys_mount+0xfc/0x1f4
>> [<06dd06e0>] ret_fast_syscall+0x0/0x48
>> [<a8308cb3>] 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
>
next prev parent reply other threads:[~2021-10-18 10:07 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-18 7:56 [V2][PATCH] cgroup: fix memory leak caused by missing cgroup_bpf_offline quanyang.wang
2021-10-18 9:02 ` Ming Lei
2021-10-18 10:06 ` Quanyang Wang [this message]
2021-10-18 12:59 ` Ming Lei
2021-10-19 10:41 ` Quanyang Wang
2021-10-19 17:10 ` Michal Koutný
2021-10-20 2:17 ` Ming Lei
2021-10-20 5:22 ` Quanyang Wang
2021-10-20 17:28 ` Michal Koutný
2021-10-22 11:03 ` Quanyang Wang
2021-10-20 5:16 ` Quanyang Wang
2021-10-19 10:41 ` Quanyang Wang
2021-10-22 1:30 ` Roman Gushchin
2021-10-22 11:55 ` Quanyang Wang
2021-10-22 21:29 ` Alexei Starovoitov
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