linux-kernel - [PATCH 9/8] cgroup: fix RCU related sparse warnings

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Date:   Thu, 22 Dec 2016 12:29:00 -0500
From:   Tejun Heo <tj@...nel.org>
To:     lizefan@...wei.com, hannes@...xchg.org
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        kernel-team@...com, Fengguang Wu <fengguang.wu@...el.com>
Subject: [PATCH 9/8] cgroup: fix RCU related sparse warnings

>From 9ca76e7e3cb885bc5701e9b1fe90c44f4aef123a Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@...nel.org>
Date: Thu, 22 Dec 2016 12:28:01 -0500

kn->priv which is a void * is used as a RCU pointer by cgroup.  When
dereferencing it, it was passing kn->priv to rcu_derefreence() without
casting it into a RCU pointer triggering address space mismatch
warning from sparse.  Fix them.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Fengguang Wu <fengguang.wu@...el.com>
---
 kernel/cgroup/cgroup-v1.c | 2 +-
 kernel/cgroup/cgroup.c    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 37be09e..465b101 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -694,7 +694,7 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 	 * @kn->priv is RCU safe.  Let's do the RCU dancing.
 	 */
 	rcu_read_lock();
-	cgrp = rcu_dereference(kn->priv);
+	cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
 	if (!cgrp || cgroup_is_dead(cgrp)) {
 		rcu_read_unlock();
 		mutex_unlock(&cgroup_mutex);
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index b6b9068..d9d82e9 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4932,7 +4932,7 @@ struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
 	 * have been or be removed at any point.  @kn->priv is RCU
 	 * protected for this access.  See css_release_work_fn() for details.
 	 */
-	cgrp = rcu_dereference(kn->priv);
+	cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
 	if (cgrp)
 		css = cgroup_css(cgrp, ss);
 
-- 
2.9.3