cpufreq: ondemand: Fix locking issue in store_powersave_bias

store_powersave_bias takes timer_mutex before calling dbs_timer_exit
which tries to cancel the delayed work do_dbs_timer which in turn
tries to take the same lock. This can cause a lock recursion under
the race condition where can cancel_delayed_work_sync is called
when the work has already started executing.

This can be avoided by taking that lock after calling
dbs_timer_exit.

Change-Id: I7f862286e66f1ddc1e13e4eeee369dd188fc10d5
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>

drivers/cpufreq/cpufreq_ondemand.c

@@ -696,15 +696,15 @@ static ssize_t store_powersave_bias(struct kobject *a, struct attribute *b,
 
 			if (dbs_info->cur_policy) {
 				/* cpu using ondemand, cancel dbs timer */
-				mutex_lock(&dbs_info->timer_mutex);
 				dbs_timer_exit(dbs_info);
 
+				mutex_lock(&dbs_info->timer_mutex);
 				ondemand_powersave_bias_setspeed(
 					dbs_info->cur_policy,
 					NULL,
 					input);
-
 				mutex_unlock(&dbs_info->timer_mutex);
+
 			}
 skip_this_cpu_bypass:
 			unlock_policy_rwsem_write(cpu);