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Message-ID: <20240206105644.41185-2-marpagan@redhat.com>
Date: Tue, 6 Feb 2024 11:56:44 +0100
From: Marco Pagani <marpagan@...hat.com>
To: Moritz Fischer <mdf@...nel.org>,
Wu Hao <hao.wu@...el.com>,
Xu Yilun <yilun.xu@...el.com>,
Tom Rix <trix@...hat.com>,
Jonathan Corbet <corbet@....net>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Alan Tull <atull@...nsource.altera.com>
Cc: Marco Pagani <marpagan@...hat.com>,
linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org,
linux-fpga@...r.kernel.org
Subject: [RFC PATCH 1/1] fpga: bridge: improve protection against low-level control module unloading
Add a module owner field to the fpga_bridge struct and use it to take
the low-level control module refcount instead of assuming that the
parent device has a driver and using its owner pointer. The owner is now
passed as an additional argument at registration time. To this end, the
function for registering a bridge has been modified to take an
additional parameter. The old registration function name is used for a
helper macro that automatically sets the module that registers the fpga
bridge as the owner. This ensures compatibility with existing low-level
control modules and reduces the chances of inadvertently registering a
bridge without setting the owner.
Update the documentation to keep it consistent with the new function for
registering a bridge.
Other changes: opportunistically move put_device() from
__fpga_bridge_get() to fpga_bridge_get() and of_fpga_bridge_get() to
improve code clarity since the device refcount is taken in these
functions.
Fixes: 21aeda950c5f ("fpga: add fpga bridge framework")
Suggested-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Suggested-by: Xu Yilun <yilun.xu@...el.com>
Signed-off-by: Marco Pagani <marpagan@...hat.com>
---
Documentation/driver-api/fpga/fpga-bridge.rst | 7 ++-
drivers/fpga/fpga-bridge.c | 61 +++++++++++--------
include/linux/fpga/fpga-bridge.h | 10 ++-
3 files changed, 47 insertions(+), 31 deletions(-)
diff --git a/Documentation/driver-api/fpga/fpga-bridge.rst b/Documentation/driver-api/fpga/fpga-bridge.rst
index 604208534095..d8cf0b592673 100644
--- a/Documentation/driver-api/fpga/fpga-bridge.rst
+++ b/Documentation/driver-api/fpga/fpga-bridge.rst
@@ -6,9 +6,12 @@ API to implement a new FPGA bridge
* struct fpga_bridge - The FPGA Bridge structure
* struct fpga_bridge_ops - Low level Bridge driver ops
-* fpga_bridge_register() - Create and register a bridge
+* __fpga_bridge_register() - Create and register a bridge
* fpga_bridge_unregister() - Unregister a bridge
+The helper macro ``fpga_bridge_register()`` can be used to ease the
+registration of a bridge.
+
.. kernel-doc:: include/linux/fpga/fpga-bridge.h
:functions: fpga_bridge
@@ -16,7 +19,7 @@ API to implement a new FPGA bridge
:functions: fpga_bridge_ops
.. kernel-doc:: drivers/fpga/fpga-bridge.c
- :functions: fpga_bridge_register
+ :functions: __fpga_bridge_register
.. kernel-doc:: drivers/fpga/fpga-bridge.c
:functions: fpga_bridge_unregister
diff --git a/drivers/fpga/fpga-bridge.c b/drivers/fpga/fpga-bridge.c
index 79c473b3c7c3..aaea612d3339 100644
--- a/drivers/fpga/fpga-bridge.c
+++ b/drivers/fpga/fpga-bridge.c
@@ -55,33 +55,26 @@ int fpga_bridge_disable(struct fpga_bridge *bridge)
}
EXPORT_SYMBOL_GPL(fpga_bridge_disable);
-static struct fpga_bridge *__fpga_bridge_get(struct device *dev,
+static struct fpga_bridge *__fpga_bridge_get(struct device *bridge_dev,
struct fpga_image_info *info)
{
struct fpga_bridge *bridge;
- int ret = -ENODEV;
- bridge = to_fpga_bridge(dev);
+ bridge = to_fpga_bridge(bridge_dev);
bridge->info = info;
- if (!mutex_trylock(&bridge->mutex)) {
- ret = -EBUSY;
- goto err_dev;
- }
+ if (!mutex_trylock(&bridge->mutex))
+ return ERR_PTR(-EBUSY);
- if (!try_module_get(dev->parent->driver->owner))
- goto err_ll_mod;
+ if (!bridge->br_ops || !try_module_get(bridge->br_ops_owner)) {
+ mutex_unlock(&bridge->mutex);
+ return ERR_PTR(-ENODEV);
+ }
dev_dbg(&bridge->dev, "get\n");
return bridge;
-
-err_ll_mod:
- mutex_unlock(&bridge->mutex);
-err_dev:
- put_device(dev);
- return ERR_PTR(ret);
}
/**
@@ -98,13 +91,18 @@ static struct fpga_bridge *__fpga_bridge_get(struct device *dev,
struct fpga_bridge *of_fpga_bridge_get(struct device_node *np,
struct fpga_image_info *info)
{
- struct device *dev;
+ struct fpga_bridge *bridge;
+ struct device *bridge_dev;
- dev = class_find_device_by_of_node(&fpga_bridge_class, np);
- if (!dev)
+ bridge_dev = class_find_device_by_of_node(&fpga_bridge_class, np);
+ if (!bridge_dev)
return ERR_PTR(-ENODEV);
- return __fpga_bridge_get(dev, info);
+ bridge = __fpga_bridge_get(bridge_dev, info);
+ if (IS_ERR(bridge))
+ put_device(bridge_dev);
+
+ return bridge;
}
EXPORT_SYMBOL_GPL(of_fpga_bridge_get);
@@ -125,6 +123,7 @@ static int fpga_bridge_dev_match(struct device *dev, const void *data)
struct fpga_bridge *fpga_bridge_get(struct device *dev,
struct fpga_image_info *info)
{
+ struct fpga_bridge *bridge;
struct device *bridge_dev;
bridge_dev = class_find_device(&fpga_bridge_class, NULL, dev,
@@ -132,7 +131,11 @@ struct fpga_bridge *fpga_bridge_get(struct device *dev,
if (!bridge_dev)
return ERR_PTR(-ENODEV);
- return __fpga_bridge_get(bridge_dev, info);
+ bridge = __fpga_bridge_get(bridge_dev, info);
+ if (IS_ERR(bridge))
+ put_device(bridge_dev);
+
+ return bridge;
}
EXPORT_SYMBOL_GPL(fpga_bridge_get);
@@ -146,7 +149,7 @@ void fpga_bridge_put(struct fpga_bridge *bridge)
dev_dbg(&bridge->dev, "put\n");
bridge->info = NULL;
- module_put(bridge->dev.parent->driver->owner);
+ module_put(bridge->br_ops_owner);
mutex_unlock(&bridge->mutex);
put_device(&bridge->dev);
}
@@ -316,18 +319,19 @@ static struct attribute *fpga_bridge_attrs[] = {
ATTRIBUTE_GROUPS(fpga_bridge);
/**
- * fpga_bridge_register - create and register an FPGA Bridge device
+ * __fpga_bridge_register - create and register an FPGA Bridge device
* @parent: FPGA bridge device from pdev
* @name: FPGA bridge name
* @br_ops: pointer to structure of fpga bridge ops
* @priv: FPGA bridge private data
+ * @owner: owner module containing the br_ops
*
* Return: struct fpga_bridge pointer or ERR_PTR()
*/
struct fpga_bridge *
-fpga_bridge_register(struct device *parent, const char *name,
- const struct fpga_bridge_ops *br_ops,
- void *priv)
+__fpga_bridge_register(struct device *parent, const char *name,
+ const struct fpga_bridge_ops *br_ops,
+ void *priv, struct module *owner)
{
struct fpga_bridge *bridge;
int id, ret;
@@ -357,6 +361,7 @@ fpga_bridge_register(struct device *parent, const char *name,
bridge->name = name;
bridge->br_ops = br_ops;
+ bridge->br_ops_owner = owner;
bridge->priv = priv;
bridge->dev.groups = br_ops->groups;
@@ -386,7 +391,7 @@ fpga_bridge_register(struct device *parent, const char *name,
return ERR_PTR(ret);
}
-EXPORT_SYMBOL_GPL(fpga_bridge_register);
+EXPORT_SYMBOL_GPL(__fpga_bridge_register);
/**
* fpga_bridge_unregister - unregister an FPGA bridge
@@ -404,6 +409,10 @@ void fpga_bridge_unregister(struct fpga_bridge *bridge)
if (bridge->br_ops->fpga_bridge_remove)
bridge->br_ops->fpga_bridge_remove(bridge);
+ mutex_lock(&bridge->mutex);
+ bridge->br_ops = NULL;
+ mutex_unlock(&bridge->mutex);
+
device_unregister(&bridge->dev);
}
EXPORT_SYMBOL_GPL(fpga_bridge_unregister);
diff --git a/include/linux/fpga/fpga-bridge.h b/include/linux/fpga/fpga-bridge.h
index 223da48a6d18..94c4edd047e5 100644
--- a/include/linux/fpga/fpga-bridge.h
+++ b/include/linux/fpga/fpga-bridge.h
@@ -45,6 +45,7 @@ struct fpga_bridge_info {
* @dev: FPGA bridge device
* @mutex: enforces exclusive reference to bridge
* @br_ops: pointer to struct of FPGA bridge ops
+ * @br_ops_owner: module containing the br_ops
* @info: fpga image specific information
* @node: FPGA bridge list node
* @priv: low level driver private date
@@ -54,6 +55,7 @@ struct fpga_bridge {
struct device dev;
struct mutex mutex; /* for exclusive reference to bridge */
const struct fpga_bridge_ops *br_ops;
+ struct module *br_ops_owner;
struct fpga_image_info *info;
struct list_head node;
void *priv;
@@ -79,10 +81,12 @@ int of_fpga_bridge_get_to_list(struct device_node *np,
struct fpga_image_info *info,
struct list_head *bridge_list);
+#define fpga_bridge_register(parent, name, br_ops, priv) \
+ __fpga_bridge_register(parent, name, br_ops, priv, THIS_MODULE)
struct fpga_bridge *
-fpga_bridge_register(struct device *parent, const char *name,
- const struct fpga_bridge_ops *br_ops,
- void *priv);
+__fpga_bridge_register(struct device *parent, const char *name,
+ const struct fpga_bridge_ops *br_ops, void *priv,
+ struct module *owner);
void fpga_bridge_unregister(struct fpga_bridge *br);
#endif /* _LINUX_FPGA_BRIDGE_H */
--
2.43.0
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