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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Linux PM list <linux-pm@vger.kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Viresh Kumar <viresh.kumar@linaro.org>
Subject: [PATCH 1/12] cpufreq: governor: Close dbs_data update race condition
Date: Thu, 18 Feb 2016 02:19 +0100	[thread overview]
Message-ID: <1592265.QLnTJA45ZD@vostro.rjw.lan> (raw)
In-Reply-To: <2938006.67J0esUvOA@vostro.rjw.lan>

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

It is possible for a dbs_data object to be updated after its
usage counter has become 0.  That may happen if governor_store()
runs (via a govenor tunable sysfs attribute write) in parallel
with cpufreq_governor_exit() called for the last cpufreq policy
associated with the dbs_data in question.  In that case, if
governor_store() acquires dbs_data->mutex right after
cpufreq_governor_exit() has released it, the ->store() callback
invoked by it may operate on dbs_data with no users.  Although
sysfs will cause the kobject_put() in cpufreq_governor_exit() to
block until governor_store() has returned, that situation may
lead to some unexpected results, depending on the implementation
of the ->store callback, and therefore it should be avoided.

To that end, modify governor_store() to check the dbs_data's
usage count before invoking the ->store() callback and return
an error if it is 0 at that point.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/cpufreq/cpufreq_governor.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-pm/drivers/cpufreq/cpufreq_governor.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq_governor.c
+++ linux-pm/drivers/cpufreq/cpufreq_governor.c
@@ -112,7 +112,7 @@ static ssize_t governor_store(struct kob
 
 	mutex_lock(&dbs_data->mutex);
 
-	if (gattr->store)
+	if (dbs_data->usage_count && gattr->store)
 		ret = gattr->store(dbs_data, buf, count);
 
 	mutex_unlock(&dbs_data->mutex);

  reply	other threads:[~2016-02-18  1:38 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-18  1:17 [PATCH 0/12] cpufreq: More governor code reorganization Rafael J. Wysocki
2016-02-18  1:19 ` Rafael J. Wysocki [this message]
2016-02-18  5:24   ` [PATCH 1/12] cpufreq: governor: Close dbs_data update race condition Viresh Kumar
2016-02-18 16:20     ` Rafael J. Wysocki
2016-02-19  2:27       ` Viresh Kumar
2016-02-19  2:34         ` Rafael J. Wysocki
2016-02-19  3:09   ` Viresh Kumar
2016-02-18  1:20 ` [PATCH 2/12] cpufreq: governor: Move io_is_busy to struct dbs_data Rafael J. Wysocki
2016-02-18  5:28   ` Viresh Kumar
2016-02-18  1:21 ` [PATCH 3/12] cpufreq: governor: Add a ->start callback for governors Rafael J. Wysocki
2016-02-18  5:36   ` Viresh Kumar
2016-02-18  1:22 ` [PATCH 4/12] cpufreq: governor: Drop unused governor callback and data fields Rafael J. Wysocki
2016-02-18  5:37   ` Viresh Kumar
2016-02-18  1:24 ` [PATCH 5/12] cpufreq: ondemand: Drop one more callback from struct od_ops Rafael J. Wysocki
2016-02-18  5:38   ` Viresh Kumar
2016-02-18  1:26 ` [PATCH 6/12] cpufreq: governor: Fix CPU load information updates via ->store Rafael J. Wysocki
2016-02-18  5:44   ` Viresh Kumar
2016-02-18 17:37     ` Rafael J. Wysocki
2016-02-18  1:28 ` [PATCH 7/12] cpufreq: ondemand: Rework the handling of powersave bias updates Rafael J. Wysocki
2016-02-18  5:53   ` Viresh Kumar
2016-02-18  1:30 ` [PATCH 8/12] cpufreq: governor: Make governor private data per-policy Rafael J. Wysocki
2016-02-18  6:03   ` Viresh Kumar
2016-02-18 17:56     ` [PATCH v2 " Rafael J. Wysocki
2016-02-19  2:36       ` Viresh Kumar
2016-02-18  1:31 ` [PATCH 9/12] cpufreq: governor: Move per-CPU data to the common code Rafael J. Wysocki
2016-02-18  6:08   ` Viresh Kumar
2016-02-18  1:32 ` [PATCH 10/12] cpufreq: governor: Relocate definitions of tuners structures Rafael J. Wysocki
2016-02-18  6:09   ` Viresh Kumar
2016-02-18 17:57     ` [PATCH v2 " Rafael J. Wysocki
2016-02-19  2:36       ` Viresh Kumar
2016-02-18  1:33 ` [PATCH 11/12] cpufreq: governor: Make dbs_data_mutex static Rafael J. Wysocki
2016-02-18  6:09   ` Viresh Kumar
2016-02-18  1:38 ` [PATCH 12/12] cpufreq: governor: Narrow down the dbs_data_mutex coverage Rafael J. Wysocki
2016-02-18  6:20   ` Viresh Kumar
2016-02-18 16:32     ` Rafael J. Wysocki
2016-02-18 17:58     ` [PATCH v2 " Rafael J. Wysocki
2016-02-19  2:38       ` Viresh Kumar

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