Hi Daniel,
Thank you for your review.
On 10/11/21 9:44 PM, Daniel Borkmann wrote:
[ +Roman ]
On 10/8/21 2:46 AM, quanyang.wang@xxxxxxxxxxxxx wrote:
From: Quanyang Wang <quanyang.wang@xxxxxxxxxxxxx>
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 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.
Fixes: 2b0d3d3e4fcfb ("percpu_ref: reduce memory footprint of
percpu_ref in fast path")
Signed-off-by: Quanyang Wang <quanyang.wang@xxxxxxxxxxxxx>
---
One of the recipients' email is wrong, so I resend this patch.
Sorry for any confusion caused.
---
kernel/cgroup/cgroup.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 570b0c97392a9..183736ad72f2b 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2187,8 +2187,10 @@ static void cgroup_kill_sb(struct super_block *sb)
* And don't kill the default root.
*/
if (list_empty(&root->cgrp.self.children) && root !=
&cgrp_dfl_root &&
- !percpu_ref_is_dying(&root->cgrp.self.refcnt))
+ !percpu_ref_is_dying(&root->cgrp.self.refcnt)) {
+ cgroup_bpf_offline(&root->cgrp);
percpu_ref_kill(&root->cgrp.self.refcnt);
+ }
cgroup_put(&root->cgrp);
Doesn't cgroup_bpf_offline() internally bump the root cgroup's refcount
via cgroup_get()?
How does this relate to the single cgroup_put() in the above line?
There is cgroup_get/put pair inside cgroup_bpf_offline.
cgroup_get() is at the beginning of cgroup_bpf_offline.
cgroup_put is called at the routine:
cgroup_bpf_offline
->percpu_ref_kill
-->cgroup_bpf_release_fn
--->cgroup_bpf_release (there is a cgroup_put() at the end of it).
So cgroup_bpf_offline can keep the balance of cgroup's refcount.
Would
have been nice to
see the commit msg elaborate more on this.
>
OK, I will add description about this in the commit msg.
Thanks,
Quanyang
kernfs_kill_sb(sb);
}
