misc: fastrpc: Reference count channel context

The channel context is referenced from the fastrpc user and might as
user space holds the file descriptor open outlive the fastrpc device,
which is removed when the remote processor is shutting down.

Reference count the channel context in order to retain this object until
all references has been relinquished.
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Mayank Chopra <mak.chopra@codeaurora.org>
Signed-off-by: Abhinav Asati <asatiabhi@codeaurora.org>
Signed-off-by: Vamsi Singamsetty <vamssi@codeaurora.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20190829092926.12037-2-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/fastrpc.c

@@ -186,6 +186,7 @@ struct fastrpc_channel_ctx {
 	struct idr ctx_idr;
 	struct list_head users;
 	struct miscdevice miscdev;
+	struct kref refcount;
 };
 
 struct fastrpc_user {
@@ -293,6 +294,25 @@ static int fastrpc_buf_alloc(struct fastrpc_user *fl, struct device *dev,
 	return 0;
 }
 
+static void fastrpc_channel_ctx_free(struct kref *ref)
+{
+	struct fastrpc_channel_ctx *cctx;
+
+	cctx = container_of(ref, struct fastrpc_channel_ctx, refcount);
+
+	kfree(cctx);
+}
+
+static void fastrpc_channel_ctx_get(struct fastrpc_channel_ctx *cctx)
+{
+	kref_get(&cctx->refcount);
+}
+
+static void fastrpc_channel_ctx_put(struct fastrpc_channel_ctx *cctx)
+{
+	kref_put(&cctx->refcount, fastrpc_channel_ctx_free);
+}
+
 static void fastrpc_context_free(struct kref *ref)
 {
 	struct fastrpc_invoke_ctx *ctx;
@@ -316,6 +336,8 @@ static void fastrpc_context_free(struct kref *ref)
 	kfree(ctx->maps);
 	kfree(ctx->olaps);
 	kfree(ctx);
+
+	fastrpc_channel_ctx_put(cctx);
 }
 
 static void fastrpc_context_get(struct fastrpc_invoke_ctx *ctx)
@@ -422,6 +444,9 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
 		fastrpc_get_buff_overlaps(ctx);
 	}
 
+	/* Released in fastrpc_context_put() */
+	fastrpc_channel_ctx_get(cctx);
+
 	ctx->sc = sc;
 	ctx->retval = -1;
 	ctx->pid = current->pid;
@@ -451,6 +476,7 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
 	spin_lock(&user->lock);
 	list_del(&ctx->node);
 	spin_unlock(&user->lock);
+	fastrpc_channel_ctx_put(cctx);
 	kfree(ctx->maps);
 	kfree(ctx->olaps);
 	kfree(ctx);
@@ -1123,6 +1149,7 @@ static int fastrpc_device_release(struct inode *inode, struct file *file)
 	}
 
 	fastrpc_session_free(cctx, fl->sctx);
+	fastrpc_channel_ctx_put(cctx);
 
 	mutex_destroy(&fl->mutex);
 	kfree(fl);
@@ -1141,6 +1168,9 @@ static int fastrpc_device_open(struct inode *inode, struct file *filp)
 	if (!fl)
 		return -ENOMEM;
 
+	/* Released in fastrpc_device_release() */
+	fastrpc_channel_ctx_get(cctx);
+
 	filp->private_data = fl;
 	spin_lock_init(&fl->lock);
 	mutex_init(&fl->mutex);
@@ -1398,10 +1428,6 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 	int i, err, domain_id = -1;
 	const char *domain;
 
-	data = devm_kzalloc(rdev, sizeof(*data), GFP_KERNEL);
-	if (!data)
-		return -ENOMEM;
-
 	err = of_property_read_string(rdev->of_node, "label", &domain);
 	if (err) {
 		dev_info(rdev, "FastRPC Domain not specified in DT\n");
@@ -1420,6 +1446,10 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 		return -EINVAL;
 	}
 
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
 	data->miscdev.minor = MISC_DYNAMIC_MINOR;
 	data->miscdev.name = kasprintf(GFP_KERNEL, "fastrpc-%s",
 				domains[domain_id]);
@@ -1428,6 +1458,8 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
 	if (err)
 		return err;
 
+	kref_init(&data->refcount);
+
 	dev_set_drvdata(&rpdev->dev, data);
 	dma_set_mask_and_coherent(rdev, DMA_BIT_MASK(32));
 	INIT_LIST_HEAD(&data->users);
@@ -1462,7 +1494,8 @@ static void fastrpc_rpmsg_remove(struct rpmsg_device *rpdev)
 
 	misc_deregister(&cctx->miscdev);
 	of_platform_depopulate(&rpdev->dev);
-	kfree(cctx);
+
+	fastrpc_channel_ctx_put(cctx);
 }
 
 static int fastrpc_rpmsg_callback(struct rpmsg_device *rpdev, void *data,