fpga: manager: add owner module and take its refcount

The current implementation of the fpga manager assumes that the low-level
module registers a driver for the parent device and uses its owner pointer
to take the module's refcount. This approach is problematic since it can
lead to a null pointer dereference while attempting to get the manager if
the parent device does not have a driver.

To address this problem, add a module owner pointer to the fpga_manager
struct and use it to take the module's refcount. Modify the functions for
registering the manager to take an additional owner module parameter and
rename them to avoid conflicts. Use the old function names for helper
macros that automatically set the module that registers the 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.

Also, update the documentation to keep it consistent with the new interface
for registering an fpga manager.

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
manager device is taken in these functions.

Fixes: 654ba4cc0f3e ("fpga manager: ensure lifetime with of_fpga_mgr_get")
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Xu Yilun <yilun.xu@intel.com>
Signed-off-by: Marco Pagani <marpagan@redhat.com>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/20240305192926.84886-1-marpagan@redhat.com
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>

1 files changed, 20 insertions, 6 deletions

diff --git a/include/linux/fpga/fpga-mgr.h b/include/linux/fpga/fpga-mgr.h
index 54f63459efd6..0d4fe068f3d8 100644
--- a/include/linux/fpga/fpga-mgr.h
+++ b/include/linux/fpga/fpga-mgr.h
@@ -201,6 +201,7 @@ 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_owner: module containing the mops
  * @priv: low level driver private date
  */
 struct fpga_manager {
@@ -210,6 +211,7 @@ struct fpga_manager {
 	enum fpga_mgr_states state;
 	struct fpga_compat_id *compat_id;
 	const struct fpga_manager_ops *mops;
+	struct module *mops_owner;
 	void *priv;
 };
 
@@ -230,18 +232,30 @@ struct fpga_manager *fpga_mgr_get(struct device *dev);
 
 void fpga_mgr_put(struct fpga_manager *mgr);
 
+#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);
 
+#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);
 
+#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);
+#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 */