On Thu, Jan 26, 2017 at 12:41:41PM +0300, Konstantin Khlebnikov wrote:
> Commit 2f5177f0fd7e ("sched/cgroup: Fix/cleanup cgroup teardown/init") moved
> sched_online_group() from css_online() to css_alloc(). It exposes half-baked
> task group into global lists before initializing generic cgroup stuff.
>
> LTP testcase (third in cgroup_regression_test) written for testing
> similar race in kernels 2.6.26-2.6.28 easily triggers this oops:
>
So nobody's run LTP against the kernel for almost a year?
>
> Here task group already linked into global RCU-protected list task_groups
> but pointer css->cgroup is still NULL.
>
> This patch reverts this chunk and moves online back to css_online().
Maybe put a comment with it that explains why this is needed?
Something along the lines of this perhaps?
/*
* Don't expose the cgroup until initialization of it is complete in the
* cgroup core. Otherwise things like cgroup_path() will return NULL
* pointers and the like.
*/
> +static int cpu_cgroup_css_online(struct cgroup_subsys_state *css)
> +{
> + struct task_group *tg = css_tg(css);
> + struct task_group *parent = css_tg(css->parent);
> +
> + if (parent)
> + sched_online_group(tg, parent);
> + return 0;
> +}
