FROMLIST: drivers: soc: add mutex to prevent response being processed twice

Add a mutex to prevent two threads from processing the same response
at the same time. This ensures responses are processed completely and
sequentially.

Bug: 34088848
CRs-Fixed: 1116015
Change-Id: Id2ef32edb939f8af2850b54bd6f6f447939c0732
Signed-off-by: Siena Richard <sienar@codeaurora.org>
Signed-off-by: Siqi Lin <siqilin@google.com>
(am from https://source.codeaurora.org/quic/la/kernel/msm-4.4/commit/?id=d3237316314c3d6f75a58192971f66e3822cd250)

drivers/soc/qcom/qdsp6v2/voice_svc.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
@@ -42,6 +42,12 @@ struct voice_svc_prvt {
 	struct list_head response_queue;
 	wait_queue_head_t response_wait;
 	spinlock_t response_lock;
+	/*
+	 * This mutex ensures responses are processed in sequential order and
+	 * that no two threads access and free the same response at the same
+	 * time.
+	 */
+	struct mutex response_mutex_lock;
 };
 
 struct apr_data {
@@ -467,6 +473,7 @@ static ssize_t voice_svc_read(struct file *file, char __user *arg,
 		goto done;
 	}
 
+	mutex_lock(&prtd->response_mutex_lock);
 	spin_lock_irqsave(&prtd->response_lock, spin_flags);
 
 	if (list_empty(&prtd->response_queue)) {
@@ -480,7 +487,7 @@ static ssize_t voice_svc_read(struct file *file, char __user *arg,
 			pr_debug("%s: Read timeout\n", __func__);
 
 			ret = -ETIMEDOUT;
-			goto done;
+			goto unlock;
 		} else if (ret > 0 && !list_empty(&prtd->response_queue)) {
 			pr_debug("%s: Interrupt recieved for response\n",
 				 __func__);
@@ -488,7 +495,7 @@ static ssize_t voice_svc_read(struct file *file, char __user *arg,
 			pr_debug("%s: Interrupted by SIGNAL %d\n",
 				 __func__, ret);
 
-			goto done;
+			goto unlock;
 		}
 
 		spin_lock_irqsave(&prtd->response_lock, spin_flags);
@@ -507,7 +514,7 @@ static ssize_t voice_svc_read(struct file *file, char __user *arg,
 		       __func__, count, size);
 
 		ret = -ENOMEM;
-		goto done;
+		goto unlock;
 	}
 
 	if (!access_ok(VERIFY_WRITE, arg, size)) {
@@ -515,7 +522,7 @@ static ssize_t voice_svc_read(struct file *file, char __user *arg,
 		       __func__);
 
 		ret = -EPERM;
-		goto done;
+		goto unlock;
 	}
 
 	ret = copy_to_user(arg, &resp->resp,
@@ -525,7 +532,7 @@ static ssize_t voice_svc_read(struct file *file, char __user *arg,
 		pr_err("%s: copy_to_user failed %d\n", __func__, ret);
 
 		ret = -EPERM;
-		goto done;
+		goto unlock;
 	}
 
 	spin_lock_irqsave(&prtd->response_lock, spin_flags);
@@ -539,6 +546,8 @@ static ssize_t voice_svc_read(struct file *file, char __user *arg,
 
 	ret = count;
 
+unlock:
+	mutex_unlock(&prtd->response_mutex_lock);
 done:
 	return ret;
 }
@@ -594,6 +603,7 @@ static int voice_svc_open(struct inode *inode, struct file *file)
 	INIT_LIST_HEAD(&prtd->response_queue);
 	init_waitqueue_head(&prtd->response_wait);
 	spin_lock_init(&prtd->response_lock);
+	mutex_init(&prtd->response_mutex_lock);
 	file->private_data = (void *)prtd;
 
 	/* Current APR implementation doesn't support session based
@@ -644,6 +654,7 @@ static int voice_svc_release(struct inode *inode, struct file *file)
 			pr_err("%s: Failed to dereg MVM %d\n", __func__, ret);
 	}
 
+	mutex_lock(&prtd->response_mutex_lock);
 	spin_lock_irqsave(&prtd->response_lock, spin_flags);
 
 	while (!list_empty(&prtd->response_queue)) {
@@ -657,6 +668,9 @@ static int voice_svc_release(struct inode *inode, struct file *file)
 	}
 
 	spin_unlock_irqrestore(&prtd->response_lock, spin_flags);
+	mutex_unlock(&prtd->response_mutex_lock);
+
+	mutex_destroy(&prtd->response_mutex_lock);
 
 	kfree(file->private_data);
 	file->private_data = NULL;