[PATCH cgroup/for-3.12 2/2] cgroup: fix cgroup_write_event_control()

Tejun Heo
2013-08-15T15:43:15Z

From ced043264c9c3f03ab3c992af17461db50421dd8 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Date: Thu, 15 Aug 2013 11:37:54 -0400

81eeaf0411 ("cgroup: make cftype->[un]register_event() deal with
cgroup_subsys_state inst ead of cgroup") updated the cftype event
methods to take @css (cgroup_subsys_state) instead of @cgroup;
however, it incorrectly used @css passed to
cgroup_write_event_control(), which the dummy_css for the cgroup as
the file is a cgroup core file. This leads to oops on event
registration.

Fix it by using the css matching the event target file. Note that
cgroup_write_event_control() now disallows cgroup core files from
being event sources. This is for simplicity and doesn't matter as
cgroup_event will be moved and made specific to memcg.

Signed-off-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
kernel/cgroup.c | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ab2a23f..6499004 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4040,10 +4040,10 @@ static void cgroup_event_ptable_queue_proc(struct file *file,
* Input must be in format '<event_fd> <control_fd> <args>'.
* Interpretation of args is defined by control file implementation.
*/
-static int cgroup_write_event_control(struct cgroup_subsys_state *css,
+static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
struct cftype *cft, const char *buffer)
{
- struct cgroup *cgrp = css->cgroup;
+ struct cgroup *cgrp = dummy_css->cgroup;
struct cgroup_event *event;
struct cgroup *cgrp_cfile;
unsigned int efd, cfd;
@@ -4065,7 +4065,7 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *css,
event = kzalloc(sizeof(*event), GFP_KERNEL);
if (!event)
return -ENOMEM;
- event->css = css;
+
INIT_LIST_HEAD(&event->list);
init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_proc);
init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
@@ -4101,6 +4101,23 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *css,
goto out_put_cfile;
}

+ if (!event->cft->ss) {
+ ret = -EBADF;
+ goto out_put_cfile;
+ }
+
+ /* determine the css of @cfile and associate @event with it */
+ rcu_read_lock();
+
+ ret = -EINVAL;
+ event->css = cgroup_css(cgrp, event->cft->ss->subsys_id);
+ if (event->css)
+ ret = 0;
+
+ rcu_read_unlock();
+ if (ret)
+ goto out_put_cfile;
+
/*
* The file to be monitored must be in the same cgroup as
* cgroup.event_control is.
@@ -4116,7 +4133,7 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *css,
goto out_put_cfile;
}

- ret = event->cft->register_event(css, event->cft,
+ ret = event->cft->register_event(event->css, event->cft,
event->eventfd, buffer);
if (ret)
goto out_put_cfile;
--
1.8.3.1