msm: mdss: Add lock to avoid release of active session in rotator

Add mutex lock to protect an active rotator session from being closed.
Without the lock, this can happen if a rotator closing IOCTL is
called from a separate thread.

CRs-Fixed: 2006159
Bug: 34328139
Change-Id: I927a0c626bdae5ef149e12979ec4befdbac1b7f7
Signed-off-by: Benjamin Chan <bkchan@codeaurora.org>
Signed-off-by: Naseer Ahmed <naseer@codeaurora.org>

drivers/video/msm/mdss/mdss_rotator.c

-/* Copyright (c) 2014-2016, The Linux Foundation. All rights reserved.
+/* Copyright (c) 2014-2017, The Linux Foundation. All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 and
@@ -2073,10 +2073,12 @@ static int mdss_rotator_config_session(struct mdss_rot_mgr *mgr,
 		return ret;
 	}
 
+	mutex_lock(&mgr->lock);
 	perf = mdss_rotator_find_session(private, config.session_id);
 	if (!perf) {
 		pr_err("No session with id=%u could be found\n",
 			config.session_id);
+		mutex_unlock(&mgr->lock);
 		return -EINVAL;
 	}
 
@@ -2099,6 +2101,7 @@ static int mdss_rotator_config_session(struct mdss_rot_mgr *mgr,
 		config.output.format);
 done:
 	ATRACE_END(__func__);
+	mutex_unlock(&mgr->lock);
 	return ret;
 }