[PATCH] opp: Invalidate current opp when draining the opp list

[Beata Michalska]

The current_opp when set, grabs additional reference on the opp,
which is then supposed to be dropped upon releasing the opp table.
Still both dev_pm_opp_remove_table and dev_pm_opp_remove_all_dynamic
will completely drain the OPPs list, including dropping the additional
reference on current_opp. This may lead to an attempt to access
memory that has already been released. Make sure that while draining
the list (in both dynamic and static cases) the current_opp gets
actually invalidated.

Fixes: 81c4d8a3c414 ("opp: Keep track of currently programmed OPP")

Signed-off-by: Beata Michalska <beata.michal...@arm.com>
---
 drivers/opp/core.c | 49 ++++++++++++++++++++++++++++++++-----------------
 1 file changed, 32 insertions(+), 17 deletions(-)

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index c268938..10e65c4 100644
--- a/drivers/opp/core.c
+++ b/drivers/opp/core.c
@@ -1502,10 +1502,39 @@ static struct dev_pm_opp *_opp_get_next(struct 
opp_table *opp_table,
        return opp;
 }
 
-bool _opp_remove_all_static(struct opp_table *opp_table)
+static int __opp_drain_list(struct opp_table *opp_table, bool dynamic)
 {
        struct dev_pm_opp *opp;
+       int count = 0;
+
+       /*
+        * Can't remove the OPP from under the lock, debugfs removal needs to
+        * happen lock less to avoid circular dependency issues.
+        */
+       while ((opp = _opp_get_next(opp_table, dynamic))) {
+               /*
+                * The current_opp has extra hold on the ref count,
+                * still the draining here will result in all of them
+                * being dropped completely, so make
+                * sure no one will try to access the current_opp
+                * afterwords
+                */
+               if (opp_table->current_opp == opp &&
+                   !(kref_read(&opp->kref) - 1))
+                       opp_table->current_opp = NULL;
+
+               dev_pm_opp_put(opp);
+               /*
+                * Note: the count here will reflect number of references
+                * dropped, not the number of opps in the list
+                */
+               ++count;
+       }
+       return count;
+}
 
+bool _opp_remove_all_static(struct opp_table *opp_table)
+{
        mutex_lock(&opp_table->lock);
 
        if (!opp_table->parsed_static_opps) {
@@ -1520,13 +1549,7 @@ bool _opp_remove_all_static(struct opp_table *opp_table)
 
        mutex_unlock(&opp_table->lock);
 
-       /*
-        * Can't remove the OPP from under the lock, debugfs removal needs to
-        * happen lock less to avoid circular dependency issues.
-        */
-       while ((opp = _opp_get_next(opp_table, false)))
-               dev_pm_opp_put(opp);
-
+       __opp_drain_list(opp_table, false);
        return true;
 }
 
@@ -1539,21 +1562,13 @@ bool _opp_remove_all_static(struct opp_table *opp_table)
 void dev_pm_opp_remove_all_dynamic(struct device *dev)
 {
        struct opp_table *opp_table;
-       struct dev_pm_opp *opp;
        int count = 0;
 
        opp_table = _find_opp_table(dev);
        if (IS_ERR(opp_table))
                return;
 
-       /*
-        * Can't remove the OPP from under the lock, debugfs removal needs to
-        * happen lock less to avoid circular dependency issues.
-        */
-       while ((opp = _opp_get_next(opp_table, true))) {
-               dev_pm_opp_put(opp);
-               count++;
-       }
+       count = __opp_drain_list(opp_table, true);
 
        /* Drop the references taken by dev_pm_opp_add() */
        while (count--)
-- 
2.7.4