On 2012/11/13 11:01, Tejun Heo wrote:
> struct cgroup is made RCU-safe by synchronize_rcu() in cgroup_diput().
but synchronize_rcu() is called before ss->destroy().
rcu_read_lock();
for_each_leaf_cfs_rq(cpu_rq(cpu), cfs_rq)
print_cfs_rq(m, cpu, cfs_rq);
-> call cgroup_path(task_group->css.cgroup);
rcu_read_unlock();
With this patch, if the above code race with cgroup_diput(), we might
end up accessing a cgroup which has been freed.
> There is no reason to use RCU safe kfree on it after it. Remove
> cgroup->rcu_head and use kfree() instead of kfree_rcu() in
> cgroup_diput().
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> ---
> include/linux/cgroup.h | 3 ---
> kernel/cgroup.c | 2 +-
> 2 files changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index d605857..9dcbfa1 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -196,9 +196,6 @@ struct cgroup {
> struct list_head pidlists;
> struct mutex pidlist_mutex;
>
> - /* For RCU-protected deletion */
> - struct rcu_head rcu_head;
> -
> /* List of events which userspace want to receive */
> struct list_head event_list;
> spinlock_t event_list_lock;
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 278752e..a91e7ad 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -893,7 +893,7 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
>
> simple_xattrs_free(&cgrp->xattrs);
>
> - kfree_rcu(cgrp, rcu_head);
> + kfree(cgrp);
This was also added to prevent a race in group scheduling code, and I think the race still
exists.
> } else {
> struct cfent *cfe = __d_cfe(dentry);
> struct cgroup *cgrp = dentry->d_parent->d_fsdata;
>
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