lkml.org 
[lkml]   [2021]   [Oct]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [V2][PATCH] cgroup: fix memory leak caused by missing cgroup_bpf_offline
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?

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

\
 
 \ /
  Last update: 2021-10-18 11:03    [W:0.102 / U:2.864 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site