Hello, Li.
On Tue, Jun 03, 2014 at 12:04:38PM +0800, Li Zefan wrote:
> static void cgroup_get(struct cgroup *cgrp)
> {
> WARN_ON_ONCE(cgroup_is_dead(cgrp));
> - css_get(&cgrp->self);
> + if (!(cgrp->self.flags & CSS_NO_REF))
> + css_get(&cgrp->self);
Hmmm? The same condition is tested by css_get(). Why should it be
tested again here?
> static void cgroup_put(struct cgroup *cgrp)
> {
> - css_put(&cgrp->self);
> + if (!(cgrp->self.flags & CSS_NO_REF))
> + css_put(&cgrp->self);
Ditto.
> @@ -1781,10 +1783,12 @@ static void cgroup_kill_sb(struct super_block *sb)
> * This prevents new mounts by disabling percpu_ref_tryget_live().
> * cgroup_mount() may wait for @root's release.
> */
> - if (css_has_online_children(&root->cgrp.self))
> + if (css_has_online_children(&root->cgrp.self)) {
> cgroup_put(&root->cgrp);
> - else
> - percpu_ref_kill(&root->cgrp.self.refcnt);
> + } else {
> + if (root != &cgrp_dfl_root)
> + percpu_ref_kill(&root->cgrp.self.refcnt);
> + }
As conceptually percpu_ref_kill() just puts the base ref and the
dfl_root's refcnt never reaches zero, it won't actually trigger.
Hmmm.... wouldn't the above leak a ref each time the default hierarchy
is unmounted tho? Shouldn't it be like the following?
if (root == &cgrp_dfl_root || css_has_online_children(...))
cgroup_put(&root->cgrp);
else
percpu_ref_kill(...);
Thanks.
--
tejun
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