remoteproc: Fix potential race condition in rproc_add

rproc_add adds the newly created remoteproc to a list for use by
rproc_get_by_phandle and then does some additional processing to finish
adding the remoteproc. This leaves a small window of time in which the
rproc is available in the list but not yet fully initialized, so if
another driver comes along and gets a handle to the rproc, it will be
invalid. Rearrange the code in rproc_add to make sure the rproc is added
to the list only after it has been successfuly initialized.

Fixes: fec47d863587 ("remoteproc: introduce rproc_get_by_phandle API")
Cc: stable@vger.kernel.org
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/remoteproc_core.c

@@ -1264,11 +1264,6 @@ int rproc_add(struct rproc *rproc)
 	if (ret < 0)
 		return ret;
 
-	/* expose to rproc_get_by_phandle users */
-	mutex_lock(&rproc_list_mutex);
-	list_add(&rproc->node, &rproc_list);
-	mutex_unlock(&rproc_list_mutex);
-
 	dev_info(dev, "%s is available\n", rproc->name);
 
 	dev_info(dev, "Note: remoteproc is still under development and considered experimental.\n");
@@ -1276,8 +1271,16 @@ int rproc_add(struct rproc *rproc)
 
 	/* create debugfs entries */
 	rproc_create_debug_dir(rproc);
+	ret = rproc_add_virtio_devices(rproc);
+	if (ret < 0)
+		return ret;
 
-	return rproc_add_virtio_devices(rproc);
+	/* expose to rproc_get_by_phandle users */
+	mutex_lock(&rproc_list_mutex);
+	list_add(&rproc->node, &rproc_list);
+	mutex_unlock(&rproc_list_mutex);
+
+	return 0;
 }
 EXPORT_SYMBOL(rproc_add);