Messages in this thread | | | Date | Fri, 6 Dec 2013 11:13:12 -0500 | From | Tejun Heo <> | Subject | Re: [PATCH cgroup/for-3.13-fixes] cgroup: fix oops in cgroup init failure path |
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Hello, Vladimir.
On Fri, Dec 06, 2013 at 11:02:07AM +0400, Vladimir Davydov wrote: > This patch fixes this bug, but I have a couple of questions regarding it. > > First, cgroup_load_subsys() also calls css_online(), and if it fails, it > calls cgroup_unload_subsys() to rollback. The latter function executes > the following command: > > offline_css(cgroup_css(cgroup_dummy_top, ss)); > > But since we failed to online_css(), cgroup_css() will return NULL > resulting in another oops.
I don't think the root css onlining fails for any existing controllers but yeah that looks wrong. Can you please send a patch?
> Second, it's not clear to me why we need the CSS_ONLINE flag at all if > we never assign css's that we fail to online to a cgroup. AFAIU we will > never see such css's, because in all places we call offline_css(), > namely cgroup_destroy_locked() (via kill_css()) and > cgroup_unload_subsys(), we use cgroup_css() which will return NULL for them.
The whole thing is in flux and will look very different in near future. I actually had patches queued which deal with the issue you spotted but they are being blocked on other changes ATM. So, yeah, there are some spurious stuff now.
> Before we get here, we call > > /* 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); > } > > If we fail to online a css, we will only call > > ss->css_free(css); > > on it skipping css_put() on parent. > > css_put() is called on parent in css_release() on normal destroy path.
You're right. I'll revise the patch.
Thanks.
-- tejun
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