stm class: Fix locking in unbinding policy path

Right now, if stm device removal has to unbind from a policy (that is,
an stm device that has STP policy, gets removed), it will trigger a
nested lock on the stm device's policy mutex.

This patch fixes the problem by moving the locking from the policy
unbinding to policy removal (configfs path), where it's actually needed;
the other caller of the policy unbinding function already takes the
mutex around the call.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hwtracing/stm/policy.c b/drivers/hwtracing/stm/policy.c
index 11ab6d0..94d3abf 100644 (file)
--- a/drivers/hwtracing/stm/policy.c
+++ b/drivers/hwtracing/stm/policy.c
@@ -272,13 +272,17 @@ void stp_policy_unbind(struct stp_policy *policy)
 {
        struct stm_device *stm = policy->stm;
 
+       /*
+        * stp_policy_release() will not call here if the policy is already
+        * unbound; other users should not either, as no link exists between
+        * this policy and anything else in that case
+        */
        if (WARN_ON_ONCE(!policy->stm))
                return;
 
-       mutex_lock(&stm->policy_mutex);
-       stm->policy = NULL;
-       mutex_unlock(&stm->policy_mutex);
+       lockdep_assert_held(&stm->policy_mutex);
 
+       stm->policy = NULL;
        policy->stm = NULL;
 
        stm_put_device(stm);
@@ -287,8 +291,16 @@ void stp_policy_unbind(struct stp_policy *policy)
 static void stp_policy_release(struct config_item *item)
 {
        struct stp_policy *policy = to_stp_policy(item);
+       struct stm_device *stm = policy->stm;
 
+       /* a policy *can* be unbound and still exist in configfs tree */
+       if (!stm)
+               return;
+
+       mutex_lock(&stm->policy_mutex);
        stp_policy_unbind(policy);
+       mutex_unlock(&stm->policy_mutex);
+
        kfree(policy);
 }