Messages in this thread | | | Subject | Re: [V2][PATCH] cgroup: fix memory leak caused by missing cgroup_bpf_offline | From | Quanyang Wang <> | Date | Mon, 18 Oct 2021 18:06:28 +0800 |
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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 >
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