device_cgroup: don't grab mutex in rcu callback

Commit 103a197c0c4e ("security/device_cgroup: lock assert fails in
dev_exception_clean()") grabs devcgroup_mutex to fix assert failure, but
a mutex can't be grabbed in rcu callback.  Since there shouldn't be any
other references when css_free is called, mutex isn't needed for list
cleanup in devcgroup_css_free().

Signed-off-by: Jerry Snitselaar <jerry.snitselaar@oracle.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Aristeu Rozanski <aris@redhat.com>
Cc: James Morris <james.l.morris@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 9 deletions

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index d794abcc4b3b..1c69e38e3a2c 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -159,6 +159,16 @@ static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
         }
 }
 
+static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
+{
+        struct dev_exception_item *ex, *tmp;
+
+        list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
+                list_del_rcu(&ex->list);
+                kfree_rcu(ex, rcu);
+        }
+}
+
 /**
  * dev_exception_clean - frees all entries of the exception list
  * @dev_cgroup: dev_cgroup with the exception list to be cleaned
@@ -167,14 +177,9 @@ static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
  */
 static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
 {
-        struct dev_exception_item *ex, *tmp;
-
         lockdep_assert_held(&devcgroup_mutex);
 
-        list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
-                list_del_rcu(&ex->list);
-                kfree_rcu(ex, rcu);
-        }
+        __dev_exception_clean(dev_cgroup);
 }
 
 /*
@@ -215,9 +220,7 @@ static void devcgroup_css_free(struct cgroup *cgroup)
         struct dev_cgroup *dev_cgroup;
 
         dev_cgroup = cgroup_to_devcgroup(cgroup);
-        mutex_lock(&devcgroup_mutex);
-        dev_exception_clean(dev_cgroup);
-        mutex_unlock(&devcgroup_mutex);
+        __dev_exception_clean(dev_cgroup);
         kfree(dev_cgroup);
 }