device_cgroup: Fix RCU list debugging warning

exceptions may be traversed using list_for_each_entry_rcu()
outside of an RCU read side critical section BUT under the
protection of decgroup_mutex. Hence add the corresponding
lockdep expression to fix the following false-positive
warning:

[    2.304417] =============================
[    2.304418] WARNING: suspicious RCU usage
[    2.304420] 5.5.4-stable #17 Tainted: G            E
[    2.304422] -----------------------------
[    2.304424] security/device_cgroup.c:355 RCU-list traversed in non-reader section!!

Signed-off-by: Amol Grover <frextrite@gmail.com>
Signed-off-by: James Morris <jmorris@namei.org>

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 43ab0ad..04375df 100644 (file)
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -354,7 +354,8 @@ static bool match_exception_partial(struct list_head *exceptions, short type,
 {
        struct dev_exception_item *ex;
 
-       list_for_each_entry_rcu(ex, exceptions, list) {
+       list_for_each_entry_rcu(ex, exceptions, list,
+                               lockdep_is_held(&devcgroup_mutex)) {
                if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))
                        continue;
                if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))