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From: Marco Pagani <marpagan@redhat.com>
To: Moritz Fischer <mdf@kernel.org>,
	Wu Hao <hao.wu@intel.com>,
	Xu Yilun <yilun.xu@intel.com>,
	Tom Rix <trix@redhat.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Marco Pagani <marpagan@redhat.com>,
	linux-kernel@vger.kernel.org,
	linux-fpga@vger.kernel.org
Subject: [RFC PATCH v4 1/1] fpga: add an owner and use it to take the low-level module's refcount
Date: Sat,  6 Jan 2024 00:15:26 +0100
Message-ID: <20240105231526.109247-2-marpagan@redhat.com>
In-Reply-To: <20240105231526.109247-1-marpagan@redhat.com>
References: <20240105231526.109247-1-marpagan@redhat.com>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

Add a module owner field to the fpga_manager struct 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 functions for registration have been modified to take an additional
owner parameter and renamed to avoid conflicts. The old function names
are now used for helper macros that automatically set the module that
registers the fpga manager as the owner. This ensures compatibility
with existing low-level control modules and reduces the chances of
registering a manager without setting the owner.

To detect when the owner module pointer becomes stale, set the mops
pointer to null during fpga_mgr_unregister() and test it before taking
the module's refcount. Use a mutex to protect against a crash that can
happen if __fpga_mgr_get() gets suspended between testing the mops
pointer and taking the refcount while the low-level module is being
unloaded.

Other changes: opportunistically move put_device() from __fpga_mgr_get()
to fpga_mgr_get() and of_fpga_mgr_get() to improve code clarity since
the device refcount in taken in these functions.

Fixes: 654ba4cc0f3e ("fpga manager: ensure lifetime with of_fpga_mgr_get")
Suggested-by: Xu Yilun <yilun.xu@intel.com>
Signed-off-by: Marco Pagani <marpagan@redhat.com>
---
 drivers/fpga/fpga-mgr.c       | 93 ++++++++++++++++++++++-------------
 include/linux/fpga/fpga-mgr.h | 80 +++++++++++++++++++++++++++---
 2 files changed, 134 insertions(+), 39 deletions(-)

diff --git a/drivers/fpga/fpga-mgr.c b/drivers/fpga/fpga-mgr.c
index 06651389c592..d7bfbdfdf2fc 100644
--- a/drivers/fpga/fpga-mgr.c
+++ b/drivers/fpga/fpga-mgr.c
@@ -664,20 +664,20 @@ static struct attribute *fpga_mgr_attrs[] = {
 };
 ATTRIBUTE_GROUPS(fpga_mgr);
 
-static struct fpga_manager *__fpga_mgr_get(struct device *dev)
+static struct fpga_manager *__fpga_mgr_get(struct device *mgr_dev)
 {
 	struct fpga_manager *mgr;
 
-	mgr = to_fpga_manager(dev);
+	mgr = to_fpga_manager(mgr_dev);
 
-	if (!try_module_get(dev->parent->driver->owner))
-		goto err_dev;
+	mutex_lock(&mgr->mops_mutex);
 
-	return mgr;
+	if (!mgr->mops || !try_module_get(mgr->mops_owner))
+		mgr = ERR_PTR(-ENODEV);
 
-err_dev:
-	put_device(dev);
-	return ERR_PTR(-ENODEV);
+	mutex_unlock(&mgr->mops_mutex);
+
+	return mgr;
 }
 
 static int fpga_mgr_dev_match(struct device *dev, const void *data)
@@ -693,12 +693,18 @@ static int fpga_mgr_dev_match(struct device *dev, const void *data)
  */
 struct fpga_manager *fpga_mgr_get(struct device *dev)
 {
-	struct device *mgr_dev = class_find_device(&fpga_mgr_class, NULL, dev,
-						   fpga_mgr_dev_match);
+	struct fpga_manager *mgr;
+	struct device *mgr_dev;
+
+	mgr_dev = class_find_device(&fpga_mgr_class, NULL, dev, fpga_mgr_dev_match);
 	if (!mgr_dev)
 		return ERR_PTR(-ENODEV);
 
-	return __fpga_mgr_get(mgr_dev);
+	mgr = __fpga_mgr_get(mgr_dev);
+	if (IS_ERR(mgr))
+		put_device(mgr_dev);
+
+	return mgr;
 }
 EXPORT_SYMBOL_GPL(fpga_mgr_get);
 
@@ -711,13 +717,18 @@ EXPORT_SYMBOL_GPL(fpga_mgr_get);
  */
 struct fpga_manager *of_fpga_mgr_get(struct device_node *node)
 {
-	struct device *dev;
+	struct fpga_manager *mgr;
+	struct device *mgr_dev;
 
-	dev = class_find_device_by_of_node(&fpga_mgr_class, node);
-	if (!dev)
+	mgr_dev = class_find_device_by_of_node(&fpga_mgr_class, node);
+	if (!mgr_dev)
 		return ERR_PTR(-ENODEV);
 
-	return __fpga_mgr_get(dev);
+	mgr = __fpga_mgr_get(mgr_dev);
+	if (IS_ERR(mgr))
+		put_device(mgr_dev);
+
+	return mgr;
 }
 EXPORT_SYMBOL_GPL(of_fpga_mgr_get);
 
@@ -727,7 +738,7 @@ EXPORT_SYMBOL_GPL(of_fpga_mgr_get);
  */
 void fpga_mgr_put(struct fpga_manager *mgr)
 {
-	module_put(mgr->dev.parent->driver->owner);
+	module_put(mgr->mops_owner);
 	put_device(&mgr->dev);
 }
 EXPORT_SYMBOL_GPL(fpga_mgr_put);
@@ -766,9 +777,10 @@ void fpga_mgr_unlock(struct fpga_manager *mgr)
 EXPORT_SYMBOL_GPL(fpga_mgr_unlock);
 
 /**
- * fpga_mgr_register_full - create and register an FPGA Manager device
+ * __fpga_mgr_register_full - create and register an FPGA Manager device
  * @parent:	fpga manager device from pdev
  * @info:	parameters for fpga manager
+ * @owner:	owner module containing the ops
  *
  * The caller of this function is responsible for calling fpga_mgr_unregister().
  * Using devm_fpga_mgr_register_full() instead is recommended.
@@ -776,7 +788,8 @@ EXPORT_SYMBOL_GPL(fpga_mgr_unlock);
  * Return: pointer to struct fpga_manager pointer or ERR_PTR()
  */
 struct fpga_manager *
-fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info)
+__fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info,
+			 struct module *owner)
 {
 	const struct fpga_manager_ops *mops = info->mops;
 	struct fpga_manager *mgr;
@@ -803,6 +816,9 @@ fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *in
 	}
 
 	mutex_init(&mgr->ref_mutex);
+	mutex_init(&mgr->mops_mutex);
+
+	mgr->mops_owner = owner;
 
 	mgr->name = info->name;
 	mgr->mops = info->mops;
@@ -841,14 +857,15 @@ fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *in
 
 	return ERR_PTR(ret);
 }
-EXPORT_SYMBOL_GPL(fpga_mgr_register_full);
+EXPORT_SYMBOL_GPL(__fpga_mgr_register_full);
 
 /**
- * fpga_mgr_register - create and register an FPGA Manager device
+ * __fpga_mgr_register - create and register an FPGA Manager device
  * @parent:	fpga manager device from pdev
  * @name:	fpga manager name
  * @mops:	pointer to structure of fpga manager ops
  * @priv:	fpga manager private data
+ * @owner:	owner module containing the ops
  *
  * The caller of this function is responsible for calling fpga_mgr_unregister().
  * Using devm_fpga_mgr_register() instead is recommended. This simple
@@ -859,8 +876,8 @@ EXPORT_SYMBOL_GPL(fpga_mgr_register_full);
  * Return: pointer to struct fpga_manager pointer or ERR_PTR()
  */
 struct fpga_manager *
-fpga_mgr_register(struct device *parent, const char *name,
-		  const struct fpga_manager_ops *mops, void *priv)
+__fpga_mgr_register(struct device *parent, const char *name,
+		    const struct fpga_manager_ops *mops, void *priv, struct module *owner)
 {
 	struct fpga_manager_info info = { 0 };
 
@@ -868,9 +885,9 @@ fpga_mgr_register(struct device *parent, const char *name,
 	info.mops = mops;
 	info.priv = priv;
 
-	return fpga_mgr_register_full(parent, &info);
+	return __fpga_mgr_register_full(parent, &info, owner);
 }
-EXPORT_SYMBOL_GPL(fpga_mgr_register);
+EXPORT_SYMBOL_GPL(__fpga_mgr_register);
 
 /**
  * fpga_mgr_unregister - unregister an FPGA manager
@@ -888,6 +905,12 @@ void fpga_mgr_unregister(struct fpga_manager *mgr)
 	 */
 	fpga_mgr_fpga_remove(mgr);
 
+	mutex_lock(&mgr->mops_mutex);
+
+	mgr->mops = NULL;
+
+	mutex_unlock(&mgr->mops_mutex);
+
 	device_unregister(&mgr->dev);
 }
 EXPORT_SYMBOL_GPL(fpga_mgr_unregister);
@@ -900,9 +923,10 @@ static void devm_fpga_mgr_unregister(struct device *dev, void *res)
 }
 
 /**
- * devm_fpga_mgr_register_full - resource managed variant of fpga_mgr_register()
+ * __devm_fpga_mgr_register_full - resource managed variant of fpga_mgr_register()
  * @parent:	fpga manager device from pdev
  * @info:	parameters for fpga manager
+ * @owner:	owner module containing the ops
  *
  * Return:  fpga manager pointer on success, negative error code otherwise.
  *
@@ -910,7 +934,8 @@ static void devm_fpga_mgr_unregister(struct device *dev, void *res)
  * function will be called automatically when the managing device is detached.
  */
 struct fpga_manager *
-devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info)
+__devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info,
+			      struct module *owner)
 {
 	struct fpga_mgr_devres *dr;
 	struct fpga_manager *mgr;
@@ -919,7 +944,7 @@ devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_inf
 	if (!dr)
 		return ERR_PTR(-ENOMEM);
 
-	mgr = fpga_mgr_register_full(parent, info);
+	mgr = __fpga_mgr_register_full(parent, info, owner);
 	if (IS_ERR(mgr)) {
 		devres_free(dr);
 		return mgr;
@@ -930,14 +955,15 @@ devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_inf
 
 	return mgr;
 }
-EXPORT_SYMBOL_GPL(devm_fpga_mgr_register_full);
+EXPORT_SYMBOL_GPL(__devm_fpga_mgr_register_full);
 
 /**
- * devm_fpga_mgr_register - resource managed variant of fpga_mgr_register()
+ * __devm_fpga_mgr_register - resource managed variant of fpga_mgr_register()
  * @parent:	fpga manager device from pdev
  * @name:	fpga manager name
  * @mops:	pointer to structure of fpga manager ops
  * @priv:	fpga manager private data
+ * @owner:	owner module containing the ops
  *
  * Return:  fpga manager pointer on success, negative error code otherwise.
  *
@@ -946,8 +972,9 @@ EXPORT_SYMBOL_GPL(devm_fpga_mgr_register_full);
  * device is detached.
  */
 struct fpga_manager *
-devm_fpga_mgr_register(struct device *parent, const char *name,
-		       const struct fpga_manager_ops *mops, void *priv)
+__devm_fpga_mgr_register(struct device *parent, const char *name,
+			 const struct fpga_manager_ops *mops, void *priv,
+			 struct module *owner)
 {
 	struct fpga_manager_info info = { 0 };
 
@@ -955,9 +982,9 @@ devm_fpga_mgr_register(struct device *parent, const char *name,
 	info.mops = mops;
 	info.priv = priv;
 
-	return devm_fpga_mgr_register_full(parent, &info);
+	return __devm_fpga_mgr_register_full(parent, &info, owner);
 }
-EXPORT_SYMBOL_GPL(devm_fpga_mgr_register);
+EXPORT_SYMBOL_GPL(__devm_fpga_mgr_register);
 
 static void fpga_mgr_dev_release(struct device *dev)
 {
diff --git a/include/linux/fpga/fpga-mgr.h b/include/linux/fpga/fpga-mgr.h
index 54f63459efd6..967540311462 100644
--- a/include/linux/fpga/fpga-mgr.h
+++ b/include/linux/fpga/fpga-mgr.h
@@ -201,6 +201,8 @@ struct fpga_manager_ops {
  * @state: state of fpga manager
  * @compat_id: FPGA manager id for compatibility check.
  * @mops: pointer to struct of fpga manager ops
+ * @mops_mutex: protects mops from low-level module removal
+ * @mops_owner: module containing the mops
  * @priv: low level driver private date
  */
 struct fpga_manager {
@@ -210,6 +212,8 @@ struct fpga_manager {
 	enum fpga_mgr_states state;
 	struct fpga_compat_id *compat_id;
 	const struct fpga_manager_ops *mops;
+	struct mutex mops_mutex;
+	struct module *mops_owner;
 	void *priv;
 };
 
@@ -222,6 +226,7 @@ void fpga_image_info_free(struct fpga_image_info *info);
 int fpga_mgr_load(struct fpga_manager *mgr, struct fpga_image_info *info);
 
 int fpga_mgr_lock(struct fpga_manager *mgr);
+
 void fpga_mgr_unlock(struct fpga_manager *mgr);
 
 struct fpga_manager *of_fpga_mgr_get(struct device_node *node);
@@ -230,18 +235,81 @@ struct fpga_manager *fpga_mgr_get(struct device *dev);
 
 void fpga_mgr_put(struct fpga_manager *mgr);
 
+/**
+ * fpga_mgr_register_full - create and register an FPGA Manager device
+ * @parent:	fpga manager device from pdev
+ * @info:	parameters for fpga manager
+ *
+ * The caller of this function is responsible for calling fpga_mgr_unregister().
+ * Using devm_fpga_mgr_register_full() instead is recommended.
+ *
+ * Return: pointer to struct fpga_manager pointer or ERR_PTR()
+ */
+#define fpga_mgr_register_full(parent, info) \
+	__fpga_mgr_register_full(parent, info, THIS_MODULE)
+
 struct fpga_manager *
-fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info);
+__fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info,
+			 struct module *owner);
+/**
+ * fpga_mgr_register - create and register an FPGA Manager device
+ * @parent:	fpga manager device from pdev
+ * @name:	fpga manager name
+ * @mops:	pointer to structure of fpga manager ops
+ * @priv:	fpga manager private data
+ *
+ * The caller of this function is responsible for calling fpga_mgr_unregister().
+ * Using devm_fpga_mgr_register() instead is recommended. This simple
+ * version of the register function should be sufficient for most users. The
+ * fpga_mgr_register_full() function is available for users that need to pass
+ * additional, optional parameters.
+ *
+ * Return: pointer to struct fpga_manager pointer or ERR_PTR()
+ */
+#define fpga_mgr_register(parent, name, mops, priv) \
+	__fpga_mgr_register(parent, name, mops, priv, THIS_MODULE)
 
 struct fpga_manager *
-fpga_mgr_register(struct device *parent, const char *name,
-		  const struct fpga_manager_ops *mops, void *priv);
+__fpga_mgr_register(struct device *parent, const char *name,
+		    const struct fpga_manager_ops *mops, void *priv, struct module *owner);
+
 void fpga_mgr_unregister(struct fpga_manager *mgr);
 
+/**
+ * devm_fpga_mgr_register_full - resource managed variant of fpga_mgr_register()
+ * @parent:	fpga manager device from pdev
+ * @info:	parameters for fpga manager
+ *
+ * Return:  fpga manager pointer on success, negative error code otherwise.
+ *
+ * This is the devres variant of fpga_mgr_register_full() for which the unregister
+ * function will be called automatically when the managing device is detached.
+ */
+#define devm_fpga_mgr_register_full(parent, info) \
+	__devm_fpga_mgr_register_full(parent, info, THIS_MODULE)
+
 struct fpga_manager *
-devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info);
+__devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info,
+			      struct module *owner);
+/**
+ * devm_fpga_mgr_register - resource managed variant of fpga_mgr_register()
+ * @parent:	fpga manager device from pdev
+ * @name:	fpga manager name
+ * @mops:	pointer to structure of fpga manager ops
+ * @priv:	fpga manager private data
+ *
+ * Return:  fpga manager pointer on success, negative error code otherwise.
+ *
+ * This is the devres variant of fpga_mgr_register() for which the
+ * unregister function will be called automatically when the managing
+ * device is detached.
+ */
+#define devm_fpga_mgr_register(parent, name, mops, priv) \
+	__devm_fpga_mgr_register(parent, name, mops, priv, THIS_MODULE)
+
 struct fpga_manager *
-devm_fpga_mgr_register(struct device *parent, const char *name,
-		       const struct fpga_manager_ops *mops, void *priv);
+__devm_fpga_mgr_register(struct device *parent, const char *name,
+			 const struct fpga_manager_ops *mops, void *priv,
+			 struct module *owner);
 
 #endif /*_LINUX_FPGA_MGR_H */
-- 
2.43.0