Quoting Tejun Heo (tj@xxxxxxxxxx):
> device_cgroup uses RCU safe ->exceptions list which is write-protected
> by devcgroup_mutex and has had some issues using locking correctly.
> Add lockdep asserts to utility functions so that future errors can be
> easily detected.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Aristeu Rozanski <aris@xxxxxxxxxx>
> Cc: Li Zefan <lizefan@xxxxxxxxxx>
> Cc: Serge E. Hallyn <serge.hallyn@xxxxxxxxxx>
Acked-by: Serge E. Hallyn <serge.hallyn@xxxxxxxxxx>
> ---
> If this looks good, I'll route it with Aristeu's earlier patch through
> cgroup/for-3.7-fixes. Thanks.
>
> security/device_cgroup.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> --- a/security/device_cgroup.c
> +++ b/security/device_cgroup.c
> @@ -82,6 +82,8 @@ static int dev_exceptions_copy(struct li
> {
> struct dev_exception_item *ex, *tmp, *new;
>
> + lockdep_assert_held(&devcgroup_mutex);
> +
> list_for_each_entry(ex, orig, list) {
> new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
> if (!new)
> @@ -107,6 +109,8 @@ static int dev_exception_add(struct dev_
> {
> struct dev_exception_item *excopy, *walk;
>
> + lockdep_assert_held(&devcgroup_mutex);
> +
> excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
> if (!excopy)
> return -ENOMEM;
> @@ -137,6 +141,8 @@ static void dev_exception_rm(struct dev_
> {
> struct dev_exception_item *walk, *tmp;
>
> + lockdep_assert_held(&devcgroup_mutex);
> +
> list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
> if (walk->type != ex->type)
> continue;
> @@ -163,6 +169,8 @@ static void dev_exception_clean(struct d
> {
> 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);
> @@ -298,6 +306,10 @@ static int may_access(struct dev_cgroup
> struct dev_exception_item *ex;
> bool match = false;
>
> + rcu_lockdep_assert(rcu_read_lock_held() ||
> + lockdep_is_held(&devcgroup_mutex),
> + "device_cgroup::may_access() called without proper synchronization");
> +
> list_for_each_entry_rcu(ex, &dev_cgroup->exceptions, list) {
> if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
> continue;
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