linux-kernel - [PATCH] component: try_module_get() to prevent unloading while in use

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Message-ID: <20220725160859.1274472-1-rf@opensource.cirrus.com>
Date:   Mon, 25 Jul 2022 17:08:59 +0100
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     <gregkh@...uxfoundation.org>, <rafael@...nel.org>
CC:     <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: [PATCH] component: try_module_get() to prevent unloading while in use

Call try_module_get() on a component before attempting to call its
bind() function, to ensure that a loadable module cannot be
unloaded while we are executing its bind().

If the bind is successful the module_put() is called only after it
has been unbound. This ensures that the module cannot be unloaded
while it is in use as an aggregate device.

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 drivers/base/component.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/base/component.c b/drivers/base/component.c
index 5eadeac6c532..01dbef4a6187 100644
--- a/drivers/base/component.c
+++ b/drivers/base/component.c
@@ -580,6 +580,8 @@ static void component_unbind(struct component *component,
 
 	/* Release all resources claimed in the binding of this component */
 	devres_release_group(component->dev, component);
+
+	module_put(component->dev->driver->owner);
 }
 
 /**
@@ -617,13 +619,18 @@ static int component_bind(struct component *component, struct aggregate_device *
 {
 	int ret;
 
+	if (!try_module_get(component->dev->driver->owner))
+		return -ENODEV;
+
 	/*
 	 * Each component initialises inside its own devres group.
 	 * This allows us to roll-back a failed component without
 	 * affecting anything else.
 	 */
-	if (!devres_open_group(adev->parent, NULL, GFP_KERNEL))
+	if (!devres_open_group(adev->parent, NULL, GFP_KERNEL)) {
+		module_put(component->dev->driver->owner);
 		return -ENOMEM;
+	}
 
 	/*
 	 * Also open a group for the device itself: this allows us
@@ -632,6 +639,7 @@ static int component_bind(struct component *component, struct aggregate_device *
 	 */
 	if (!devres_open_group(component->dev, component, GFP_KERNEL)) {
 		devres_release_group(adev->parent, NULL);
+		module_put(component->dev->driver->owner);
 		return -ENOMEM;
 	}
 
-- 
2.30.2