Re: [PATCH 06/17] cgroup: remove duplicate RCU free on struct cgroup
From: Li Zefan <hidden>
Date: 2012-11-19 09:02:52
Also in:
lkml
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.
quoted hunk ↗ jump to hunk
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 <redacted> --- 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;