device_cgroup: Fix RCU list debugging warning

frextrite · James Morris · commit bc62d68e2a0a · 2020-08-20T11:25:03.000-07:00
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
@@ -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))

Original file line number	Diff line number	Diff line change
`@@ -354,7 +354,8 @@ static bool match_exception_partial(struct list_head *exceptions, short type,`
`354`	`354`	`{`
`355`	`355`	`struct dev_exception_item *ex;`
`356`	`356`
`357`		`- list_for_each_entry_rcu(ex, exceptions, list) {`
	`357`	`+ list_for_each_entry_rcu(ex, exceptions, list,`
	`358`	`+ lockdep_is_held(&devcgroup_mutex)) {`
`358`	`359`	`if ((type & DEVCG_DEV_BLOCK) && !(ex->type & DEVCG_DEV_BLOCK))`
`359`	`360`	`continue;`
`360`	`361`	`if ((type & DEVCG_DEV_CHAR) && !(ex->type & DEVCG_DEV_CHAR))`