Okay, re-sequencing the for_each_css patch turns out to be a lot more
headache than expected. Let's just fix it up in this patch proper.
It's a standalone bug fix anyway. The change only affects the
for_each_css() patch later. Will post an updated version of that
patch too soon.
Thanks.
----- 8< -----
ae7f164a09 ("cgroup: move cgroup->subsys[] assignment to
online_css()") moved cgroup->subsys[] assignements later in
cgroup_create() but didn't update error handling path accordingly
leaking later css's after an online_css() failure.
This patch moves reference bumping inside online_css() loop, clears
css_ar[] as css's are brought online successfully, and updates
err_destroy path so that either a css is fully online and destroyed by
cgroup_destroy_locked() or the error path frees it. This creates a
duplicate css free logic in the error path but it will be cleaned up
soon.
v2: Li pointed out that cgroup_destroy_locked() would do NULL-deref if
invoked with a cgroup which doesn't have all css's populated.
Update cgroup_destroy_locked() so that it skips NULL css's.
Signed-off-by: Tejun Heo <t...@kernel.org>
Cc: Li Zefan <lize...@huawei.com>
---
kernel/cgroup.c | 31 +++++++++++++++++++++----------
1 file changed, 21 insertions(+), 10 deletions(-)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4489,14 +4489,6 @@ static long cgroup_create(struct cgroup
list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children);
root->number_of_cgroups++;
- /* each css holds a ref to the cgroup's dentry and the parent css */
- for_each_root_subsys(root, ss) {
- struct cgroup_subsys_state *css = css_ar[ss->subsys_id];
-
- dget(dentry);
- css_get(css->parent);
- }
-
/* hold a ref to the parent's dentry */
dget(parent->dentry);
@@ -4508,6 +4500,13 @@ static long cgroup_create(struct cgroup
if (err)
goto err_destroy;
+ /* each css holds a ref to the cgroup's dentry and parent css */
+ dget(dentry);
+ css_get(css->parent);
+
+ /* mark it consumed for error path */
+ css_ar[ss->subsys_id] = NULL;
+
if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
parent->parent) {
pr_warning("cgroup: %s (%d) created nested cgroup for
controller \"%s\" which has incomplete hierarchy support. Nested cgroups may
change behavior in the future.\n",
@@ -4554,6 +4553,14 @@ err_free_cgrp:
return err;
err_destroy:
+ for_each_root_subsys(root, ss) {
+ struct cgroup_subsys_state *css = css_ar[ss->subsys_id];
+
+ if (css) {
+ percpu_ref_cancel_init(&css->refcnt);
+ ss->css_free(css);
+ }
+ }
cgroup_destroy_locked(cgrp);
mutex_unlock(&cgroup_mutex);
mutex_unlock(&dentry->d_inode->i_mutex);
@@ -4698,8 +4705,12 @@ static int cgroup_destroy_locked(struct
* will be invoked to perform the rest of destruction once the
* percpu refs of all css's are confirmed to be killed.
*/
- for_each_root_subsys(cgrp->root, ss)
- kill_css(cgroup_css(cgrp, ss));
+ for_each_root_subsys(cgrp->root, ss) {
+ struct cgroup_subsys_state *css = cgroup_css(cgrp, ss);
+
+ if (css)
+ kill_css(css);
+ }
/*
* Mark @cgrp dead. This prevents further task migration and child
--
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