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cgroup: make cgroup_event hold onto cgroup_subsys_state instead of cgroup 

Currently, each registered cgroup_event holds an extra reference to
the cgroup.  This is a bit weird as events are subsystem specific and
will also be incorrect in the planned unified hierarchy as css
(cgroup_subsys_state) may come and go dynamically across the lifetime
of a cgroup.  Holding onto cgroup won't prevent the target css from
going away.

Update cgroup_event to hold onto the css the traget file belongs to
instead of cgroup.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
This commit is contained in:
Tejun Heo 2013-08-26 18:40:56 -04:00
parent 9fa4db334c
commit 7941cb027d
1 changed files with 12 additions and 14 deletions
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26
kernel/cgroup.c
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@ -3969,7 +3969,6 @@ static void cgroup_event_remove(struct work_struct *work)
struct cgroup_event *event = container_of(work, struct cgroup_event,
remove);
struct cgroup_subsys_state *css = event->css;
struct cgroup *cgrp = css->cgroup;
remove_wait_queue(event->wqh, &event->wait);
@ -3980,7 +3979,7 @@ static void cgroup_event_remove(struct work_struct *work)
eventfd_ctx_put(event->eventfd);
kfree(event);
cgroup_dput(cgrp);
css_put(css);
}
/*
@ -4103,12 +4102,16 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
goto out_put_cfile;
}
/* determine the css of @cfile and associate @event with it */
/*
* Determine the css of @cfile and associate @event with it.
* Remaining events are automatically removed on cgroup destruction
* but the removal is asynchronous, so take an extra ref.
*/
rcu_read_lock();
ret = -EINVAL;
event->css = cgroup_css(cgrp, event->cft->ss);
if (event->css)
if (event->css && css_tryget(event->css))
ret = 0;
rcu_read_unlock();
@ -4122,28 +4125,21 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
cgrp_cfile = __d_cgrp(cfile->f_dentry->d_parent);
if (cgrp_cfile != cgrp) {
ret = -EINVAL;
goto out_put_cfile;
goto out_put_css;
}
if (!event->cft->register_event || !event->cft->unregister_event) {
ret = -EINVAL;
goto out_put_cfile;
goto out_put_css;
}
ret = event->cft->register_event(event->css, event->cft,
event->eventfd, buffer);
if (ret)
goto out_put_cfile;
goto out_put_css;
efile->f_op->poll(efile, &event->pt);
/*
* Events should be removed after rmdir of cgroup directory, but before
* destroying subsystem state objects. Let's take reference to cgroup
* directory dentry to do that.
*/
dget(cgrp->dentry);
spin_lock(&cgrp->event_list_lock);
list_add(&event->list, &cgrp->event_list);
spin_unlock(&cgrp->event_list_lock);
@ -4153,6 +4149,8 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
return 0;
out_put_css:
css_put(event->css);
out_put_cfile:
fput(cfile);
out_put_eventfd: