linux-kernel - [PATCH 04/14] device_cgroup: remove direct access to cgroup->children

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Date:	Fri,  9 May 2014 17:31:21 -0400
From:	Tejun Heo <tj@...nel.org>
To:	lizefan@...wei.com
Cc:	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	hannes@...xchg.org, Tejun Heo <tj@...nel.org>,
	Aristeu Rozanski <aris@...hat.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>
Subject: [PATCH 04/14] device_cgroup: remove direct access to cgroup->children

Currently, devcg::has_children() directly tests cgroup->children for
list emptiness.  The field is not a published field and scheduled to
go away.  In addition, the test isn't strictly correct as devcg should
only care about children which are visible to userland.

This patch converts has_children() to use css_next_child() instead.
The subtle incorrectness is noted and will be dealt with later.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Aristeu Rozanski <aris@...hat.com>
Cc: Serge Hallyn <serge.hallyn@...ntu.com>
---
 security/device_cgroup.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 3116015..75b4b18 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -477,9 +477,17 @@ static int propagate_exception(struct dev_cgroup *devcg_root,
 
 static inline bool has_children(struct dev_cgroup *devcgroup)
 {
-	struct cgroup *cgrp = devcgroup->css.cgroup;
+	bool ret;
 
-	return !list_empty(&cgrp->children);
+	/*
+	 * FIXME: There may be lingering offline csses and this function
+	 * may return %true when there isn't any userland-visible child
+	 * which is incorrect for our purposes.
+	 */
+	rcu_read_lock();
+	ret = css_next_child(NULL, &devcgroup->css);
+	rcu_read_unlock();
+	return ret;
 }
 
 /*
-- 
1.9.0

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