[PATCH v3 2/2] cpufreq: Serialize global boost updates

[Christian Loehle]

Concurrent global boost sysfs writes can interleave their global flag
and per-policy updates. An enabling write can set the global flag, then
a disabling write can clear it and finish before the enabling write
updates the policies. Both writes succeed, leaving boost enabled on
the policies while the global flag is disabled.

Serialize the complete global boost update, including rollback on
failure, with a mutex.

Fixes: 6f19efc0a1ca ("cpufreq: Add boost frequency support in core")
Signed-off-by: Christian Loehle <christian.loehle@xxxxxxx>
Reviewed-by: Pengjie Zhang <zhangpengjie2@xxxxxxxxxx>
Reviewed-by: Zhongqiu Han <zhongqiu.han@xxxxxxxxxxxxxxxx>
Reviewed-by: Sumit Gupta <sumitg@xxxxxxxxxx>
---
 drivers/cpufreq/cpufreq.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 23a77f5524df..d95c849f79c5 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2810,6 +2810,8 @@ int cpufreq_boost_set_sw(struct cpufreq_policy *policy, int state)
 }
 EXPORT_SYMBOL_GPL(cpufreq_boost_set_sw);
 
+static DEFINE_MUTEX(cpufreq_boost_mutex);
+
 static int cpufreq_boost_trigger_state(int state)
 {
 	struct cpufreq_policy *policy;
@@ -2817,6 +2819,8 @@ static int cpufreq_boost_trigger_state(int state)
 	bool boost_enabled;
 	int ret = -EOPNOTSUPP;
 
+	guard(mutex)(&cpufreq_boost_mutex);
+
 	/*
 	 * Don't compare 'cpufreq_driver->boost_enabled' with 'state' here to
 	 * make sure all policies are in sync with global boost flag.
-- 
2.34.1