linux-kernel - Re: [PATCH] opp: Reinitialize the list_kref before adding the static OPPs again

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date:   Mon, 11 Nov 2019 17:01:17 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Nishanth Menon <nm@...com>, Viresh Kumar <vireshk@...nel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Dmitry Osipenko <digetx@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] opp: Reinitialize the list_kref before adding the static
 OPPs again

On 11-11-19, 13:51, Viresh Kumar wrote:
> On 30-10-19, 07:33, Stephen Boyd wrote:
> > I agree a simple refcount_t makes more sense here instead of using a
> > kref. That would be clearer.
> 
> I was using kref as I wanted to call the cleanup routine when kref
> reaches 0. A refcount_t will have the same problem as the warning in
> this came from refcount mechanism only (which is used by kref). You
> can't increment a refcount_t if it is zero :)
> 
> Any other suggestions other than local counting ?

i.e. something like this, untested.

---
 drivers/opp/core.c | 26 ++++++++------------------
 drivers/opp/of.c   | 14 +++++---------
 drivers/opp/opp.h  |  6 ++----
 3 files changed, 15 insertions(+), 31 deletions(-)

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index 467b2348a289..ea1d89177511 100644
--- a/drivers/opp/core.c
+++ b/drivers/opp/core.c
@@ -988,7 +988,6 @@ static struct opp_table *_allocate_opp_table(struct device *dev, int index)
 	BLOCKING_INIT_NOTIFIER_HEAD(&opp_table->head);
 	INIT_LIST_HEAD(&opp_table->opp_list);
 	kref_init(&opp_table->kref);
-	kref_init(&opp_table->list_kref);
 
 	/* Secure the device table modification */
 	list_add(&opp_table->node, &opp_tables);
@@ -1076,27 +1075,18 @@ static void _opp_remove_all_static(struct opp_table *opp_table)
 {
 	struct dev_pm_opp *opp, *tmp;
 
+	mutex_lock(&opp_table->lock);
+
+	if (!opp_table->parsed_static_opps || --opp_table->parsed_static_opps)
+		goto unlock;
+
 	list_for_each_entry_safe(opp, tmp, &opp_table->opp_list, node) {
 		if (!opp->dynamic)
 			dev_pm_opp_put(opp);
 	}
 
-	opp_table->parsed_static_opps = false;
-}
-
-static void _opp_table_list_kref_release(struct kref *kref)
-{
-	struct opp_table *opp_table = container_of(kref, struct opp_table,
-						   list_kref);
-
-	_opp_remove_all_static(opp_table);
-	mutex_unlock(&opp_table_lock);
-}
-
-void _put_opp_list_kref(struct opp_table *opp_table)
-{
-	kref_put_mutex(&opp_table->list_kref, _opp_table_list_kref_release,
-		       &opp_table_lock);
+unlock:
+	mutex_unlock(&opp_table->lock);
 }
 
 void dev_pm_opp_put_opp_table(struct opp_table *opp_table)
@@ -2276,7 +2266,7 @@ void _dev_pm_opp_find_and_remove_table(struct device *dev)
 		return;
 	}
 
-	_put_opp_list_kref(opp_table);
+	_opp_remove_all_static(opp_table);
 
 	/* Drop reference taken by _find_opp_table() */
 	dev_pm_opp_put_opp_table(opp_table);
diff --git a/drivers/opp/of.c b/drivers/opp/of.c
index 1cbb58240b80..2c433e9f9223 100644
--- a/drivers/opp/of.c
+++ b/drivers/opp/of.c
@@ -658,17 +658,15 @@ static int _of_add_opp_table_v2(struct device *dev, struct opp_table *opp_table)
 	struct dev_pm_opp *opp;
 
 	/* OPP table is already initialized for the device */
+	mutex_lock(&opp_table->lock);
 	if (opp_table->parsed_static_opps) {
-		kref_get(&opp_table->list_kref);
+		opp_table->parsed_static_opps++;
+		mutex_unlock(&opp_table->lock);
 		return 0;
 	}
 
-	/*
-	 * Re-initialize list_kref every time we add static OPPs to the OPP
-	 * table as the reference count may be 0 after the last tie static OPPs
-	 * were removed.
-	 */
-	kref_init(&opp_table->list_kref);
+	opp_table->parsed_static_opps = 1;
+	mutex_unlock(&opp_table->lock);
 
 	/* We have opp-table node now, iterate over it and add OPPs */
 	for_each_available_child_of_node(opp_table->np, np) {
@@ -701,8 +699,6 @@ static int _of_add_opp_table_v2(struct device *dev, struct opp_table *opp_table)
 	if (pstate_count)
 		opp_table->genpd_performance_state = true;
 
-	opp_table->parsed_static_opps = true;
-
 	return 0;
 }
 
diff --git a/drivers/opp/opp.h b/drivers/opp/opp.h
index 51ad942d1b6b..4e69b855a6a0 100644
--- a/drivers/opp/opp.h
+++ b/drivers/opp/opp.h
@@ -127,11 +127,10 @@ enum opp_table_access {
  * @dev_list:	list of devices that share these OPPs
  * @opp_list:	table of opps
  * @kref:	for reference count of the table.
- * @list_kref:	for reference count of the OPP list.
  * @lock:	mutex protecting the opp_list and dev_list.
  * @np:		struct device_node pointer for opp's DT node.
  * @clock_latency_ns_max: Max clock latency in nanoseconds.
- * @parsed_static_opps: True if OPPs are initialized from DT.
+ * @parsed_static_opps: Count of devices for which OPPs are initialized from DT.
  * @shared_opp: OPP is shared between multiple devices.
  * @suspend_opp: Pointer to OPP to be used during device suspend.
  * @genpd_virt_dev_lock: Mutex protecting the genpd virtual device pointers.
@@ -167,7 +166,6 @@ struct opp_table {
 	struct list_head dev_list;
 	struct list_head opp_list;
 	struct kref kref;
-	struct kref list_kref;
 	struct mutex lock;
 
 	struct device_node *np;
@@ -176,7 +174,7 @@ struct opp_table {
 	/* For backward compatibility with v1 bindings */
 	unsigned int voltage_tolerance_v1;
 
-	bool parsed_static_opps;
+	unsigned int parsed_static_opps;
 	enum opp_table_access shared_opp;
 	struct dev_pm_opp *suspend_opp;

-- 
viresh