stm class: Rework policy node fallback

Currently, if no matching policy node can be found for a trace source,
we'll try to use "default" policy node, then, if that doesn't exist,
we'll pick the first node, in order of creation. If that also fails,
we'll allocate M/C range from the beginning of the device's M/C range.

This makes it difficult to know which node (if any) was used in any
particular case.

In order to make things more deterministic, the new order is as follows:
  * if they supply ID string, use that and nothing else,
  * if they are a task, use their task name (comm),
  * use "default", if it exists,
  * return failure, to let them know there is no suitable rule.

This should provide enough convenience with the "default" catch-all node,
while not leaving *everything* to chance. As a side effect, this relaxes
the requirement of using ioctl() for identification with the possibility of
using task names as policy nodes.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Tested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 6 deletions

diff --git a/drivers/hwtracing/stm/policy.c b/drivers/hwtracing/stm/policy.c
index 3fd07e275b34..15d35d891643 100644
--- a/drivers/hwtracing/stm/policy.c
+++ b/drivers/hwtracing/stm/policy.c
@@ -392,7 +392,7 @@ static struct configfs_subsystem stp_policy_subsys = {
 static struct stp_policy_node *
 __stp_policy_node_lookup(struct stp_policy *policy, char *s)
 {
-	struct stp_policy_node *policy_node, *ret;
+	struct stp_policy_node *policy_node, *ret = NULL;
 	struct list_head *head = &policy->group.cg_children;
 	struct config_item *item;
 	char *start, *end = s;
@@ -400,10 +400,6 @@ __stp_policy_node_lookup(struct stp_policy *policy, char *s)
 	if (list_empty(head))
 		return NULL;
 
-	/* return the first entry if everything else fails */
-	item = list_entry(head->next, struct config_item, ci_entry);
-	ret = to_stp_policy_node(item);
-
 next:
 	for (;;) {
 		start = strsep(&end, "/");
@@ -449,13 +445,17 @@ stp_policy_node_lookup(struct stm_device *stm, char *s)
 
 	if (policy_node)
 		config_item_get(&policy_node->group.cg_item);
-	mutex_unlock(&stp_policy_subsys.su_mutex);
+	else
+		mutex_unlock(&stp_policy_subsys.su_mutex);
 
 	return policy_node;
 }
 
 void stp_policy_node_put(struct stp_policy_node *policy_node)
 {
+	lockdep_assert_held(&stp_policy_subsys.su_mutex);
+
+	mutex_unlock(&stp_policy_subsys.su_mutex);
 	config_item_put(&policy_node->group.cg_item);
 }