Revert "rpmsg: core: fix race in driver_override_show() and use core helper"

This reverts commit 392c6b68334aa0e0ae9aba95c0a366bcb0d92f5d which is
commit 42023d4b6d2661a40ee2dcf7e1a3528a35c638ca upstream.

It breaks the Android kernel build and can be brought back in the future
in an safe way if it is really needed.

Bug: 161946584
Change-Id: If610464bc9786130e2dfe2badfb07841417cac76
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/rpmsg/rpmsg_core.c

diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
index 963cdce..3c6fd03 100644
--- a/drivers/rpmsg/rpmsg_core.c
+++ b/drivers/rpmsg/rpmsg_core.c
@@ -362,38 +362,50 @@ field##_show(struct device *dev,					\
 }									\
 static DEVICE_ATTR_RO(field);
 
+#define rpmsg_string_attr(field, member)				\
+static ssize_t								\
+field##_store(struct device *dev, struct device_attribute *attr,	\
+	      const char *buf, size_t sz)				\
+{									\
+	struct rpmsg_device *rpdev = to_rpmsg_device(dev);		\
+	const char *old;						\
+	char *new;							\
+									\
+	new = kstrndup(buf, sz, GFP_KERNEL);				\
+	if (!new)							\
+		return -ENOMEM;						\
+	new[strcspn(new, "\n")] = '\0';					\
+									\
+	device_lock(dev);						\
+	old = rpdev->member;						\
+	if (strlen(new)) {						\
+		rpdev->member = new;					\
+	} else {							\
+		kfree(new);						\
+		rpdev->member = NULL;					\
+	}								\
+	device_unlock(dev);						\
+									\
+	kfree(old);							\
+									\
+	return sz;							\
+}									\
+static ssize_t								\
+field##_show(struct device *dev,					\
+	     struct device_attribute *attr, char *buf)			\
+{									\
+	struct rpmsg_device *rpdev = to_rpmsg_device(dev);		\
+									\
+	return sprintf(buf, "%s\n", rpdev->member);			\
+}									\
+static DEVICE_ATTR_RW(field)
+
 /* for more info, see Documentation/ABI/testing/sysfs-bus-rpmsg */
 rpmsg_show_attr(name, id.name, "%s\n");
 rpmsg_show_attr(src, src, "0x%x\n");
 rpmsg_show_attr(dst, dst, "0x%x\n");
 rpmsg_show_attr(announce, announce ? "true" : "false", "%s\n");
-
-static ssize_t driver_override_store(struct device *dev,
-				     struct device_attribute *attr,
-				     const char *buf, size_t count)
-{
-	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
-	int ret;
-
-	ret = driver_set_override(dev, &rpdev->driver_override, buf, count);
-	if (ret)
-		return ret;
-
-	return count;
-}
-
-static ssize_t driver_override_show(struct device *dev,
-				    struct device_attribute *attr, char *buf)
-{
-	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
-	ssize_t len;
-
-	device_lock(dev);
-	len = sysfs_emit(buf, "%s\n", rpdev->driver_override);
-	device_unlock(dev);
-	return len;
-}
-static DEVICE_ATTR_RW(driver_override);
+rpmsg_string_attr(driver_override, driver_override);
 
 static ssize_t modalias_show(struct device *dev,
 			     struct device_attribute *attr, char *buf)