linux-kernel - [PATCH] platform: Provide a remove callback that returns no value

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Message-Id: <20221209150914.3557650-1-u.kleine-koenig@pengutronix.de>
Date:   Fri,  9 Dec 2022 16:09:14 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de
Subject: [PATCH] platform: Provide a remove callback that returns no value

struct platform_driver::remove returning an integer made driver authors
expect that returning an error code was proper error handling. However
the driver core ignores the error and continues to remove the device
because there is nothing the core could do anyhow and reentering the
remove callback again is only calling for trouble.

So this is an source for errors typically yielding resource leaks in the
error path.

As there are too many platform drivers to neatly convert them all to
return void in a single go, do it in several steps after this patch:

 a) Convert all drivers to implement .remove_new() returning void instead
    of .remove() returning int;
 b) Change struct platform_driver::remove() to return void and so make
    it identical to .remove_new();
 c) Change all drivers back to .remove() now with the better prototype;
 d) drop struct platform_driver::remove_new().

While this touches all drivers eventually twice, steps a) and c) can be
done one driver after another and so reduces coordination efforts
immensely and simplifies review.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
---
 drivers/base/platform.c         |  4 +++-
 include/linux/platform_device.h | 11 +++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 968f3d71eeab..a4938d1c8fe1 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -1416,7 +1416,9 @@ static void platform_remove(struct device *_dev)
 	struct platform_driver *drv = to_platform_driver(_dev->driver);
 	struct platform_device *dev = to_platform_device(_dev);
 
-	if (drv->remove) {
+	if (drv->remove_new) {
+		drv->remove_new(dev);
+	} else if (drv->remove) {
 		int ret = drv->remove(dev);
 
 		if (ret)
diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
index b0d5a253156e..b845fd83f429 100644
--- a/include/linux/platform_device.h
+++ b/include/linux/platform_device.h
@@ -207,7 +207,18 @@ extern void platform_device_put(struct platform_device *pdev);
 
 struct platform_driver {
 	int (*probe)(struct platform_device *);
+
+	/*
+	 * Traditionally the remove callback returned an int which however is
+	 * ignored by the driver core. This led to wrong expectations by driver
+	 * authors who thought returning an error code was a valid error
+	 * handling strategy. To convert to a callback returning void, new
+	 * drivers should implement .remove_new() until the conversion it done
+	 * that eventually makes .remove() return void.
+	 */
 	int (*remove)(struct platform_device *);
+	void (*remove_new)(struct platform_device *);
+
 	void (*shutdown)(struct platform_device *);
 	int (*suspend)(struct platform_device *, pm_message_t state);
 	int (*resume)(struct platform_device *);
-- 
2.38.1