Messages in this thread | | | Date | Tue, 3 Jun 2014 08:57:28 -0400 | From | Tejun Heo <> | Subject | Re: [PATCH 1/3] cgroup: don't destroy the default root |
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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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