cxl/pci: Introduce cdevm_file_operations

In preparation for moving cxl_memdev allocation to the core, introduce
cdevm_file_operations to coordinate file operations shutdown relative to
driver data release.

The motivation for moving cxl_memdev allocation to the core (beyond
better file organization of sysfs attributes in core/ and drivers in
cxl/), is that device lifetime is longer than module lifetime. The cxl_pci
module should be free to come and go without needing to coordinate with
devices that need the text associated with cxl_memdev_release() to stay
resident. The move will fix a use after free bug when looping driver
load / unload with CONFIG_DEBUG_KOBJECT_RELEASE=y.

Another motivation for passing in file_operations to the core cxl_memdev
creation flow is to allow for alternate drivers, like unit test code, to
define their own ioctl backends.
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/162792539962.368511.2962268954245340288.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/cxlmem.h

@@ -34,6 +34,21 @@
  */
 #define CXL_MEM_MAX_DEVS 65536
 
+/**
+ * struct cdevm_file_operations - devm coordinated cdev file operations
+ * @fops: file operations that are synchronized against @shutdown
+ * @shutdown: disconnect driver data
+ *
+ * @shutdown is invoked in the devres release path to disconnect any
+ * driver instance data from @dev. It assumes synchronization with any
+ * fops operation that requires driver data. After @shutdown an
+ * operation may only reference @device data.
+ */
+struct cdevm_file_operations {
+	struct file_operations fops;
+	void (*shutdown)(struct device *dev);
+};
+
 /**
  * struct cxl_memdev - CXL bus object representing a Type-3 Memory Device
  * @dev: driver core device object

drivers/cxl/pci.c

@@ -806,13 +806,30 @@ static int cxl_memdev_release_file(struct inode *inode, struct file *file)
 	return 0;
 }
 
-static const struct file_operations cxl_memdev_fops = {
-	.owner = THIS_MODULE,
-	.unlocked_ioctl = cxl_memdev_ioctl,
-	.open = cxl_memdev_open,
-	.release = cxl_memdev_release_file,
-	.compat_ioctl = compat_ptr_ioctl,
-	.llseek = noop_llseek,
+static struct cxl_memdev *to_cxl_memdev(struct device *dev)
+{
+	return container_of(dev, struct cxl_memdev, dev);
+}
+
+static void cxl_memdev_shutdown(struct device *dev)
+{
+	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
+
+	down_write(&cxl_memdev_rwsem);
+	cxlmd->cxlm = NULL;
+	up_write(&cxl_memdev_rwsem);
+}
+
+static const struct cdevm_file_operations cxl_memdev_fops = {
+	.fops = {
+		.owner = THIS_MODULE,
+		.unlocked_ioctl = cxl_memdev_ioctl,
+		.open = cxl_memdev_open,
+		.release = cxl_memdev_release_file,
+		.compat_ioctl = compat_ptr_ioctl,
+		.llseek = noop_llseek,
+	},
+	.shutdown = cxl_memdev_shutdown,
 };
 
 static inline struct cxl_mem_command *cxl_mem_find_command(u16 opcode)
@@ -1161,11 +1178,6 @@ static int cxl_mem_setup_regs(struct cxl_mem *cxlm)
 	return ret;
 }
 
-static struct cxl_memdev *to_cxl_memdev(struct device *dev)
-{
-	return container_of(dev, struct cxl_memdev, dev);
-}
-
 static void cxl_memdev_release(struct device *dev)
 {
 	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
@@ -1281,24 +1293,22 @@ static const struct device_type cxl_memdev_type = {
 	.groups = cxl_memdev_attribute_groups,
 };
 
-static void cxl_memdev_shutdown(struct cxl_memdev *cxlmd)
-{
-	down_write(&cxl_memdev_rwsem);
-	cxlmd->cxlm = NULL;
-	up_write(&cxl_memdev_rwsem);
-}
-
 static void cxl_memdev_unregister(void *_cxlmd)
 {
 	struct cxl_memdev *cxlmd = _cxlmd;
 	struct device *dev = &cxlmd->dev;
+	struct cdev *cdev = &cxlmd->cdev;
+	const struct cdevm_file_operations *cdevm_fops;
+
+	cdevm_fops = container_of(cdev->ops, typeof(*cdevm_fops), fops);
+	cdevm_fops->shutdown(dev);
 
 	cdev_device_del(&cxlmd->cdev, dev);
-	cxl_memdev_shutdown(cxlmd);
 	put_device(dev);
 }
 
-static struct cxl_memdev *cxl_memdev_alloc(struct cxl_mem *cxlm)
+static struct cxl_memdev *cxl_memdev_alloc(struct cxl_mem *cxlm,
+					   const struct file_operations *fops)
 {
 	struct pci_dev *pdev = cxlm->pdev;
 	struct cxl_memdev *cxlmd;
@@ -1324,7 +1334,7 @@ static struct cxl_memdev *cxl_memdev_alloc(struct cxl_mem *cxlm)
 	device_set_pm_not_required(dev);
 
 	cdev = &cxlmd->cdev;
-	cdev_init(cdev, &cxl_memdev_fops);
+	cdev_init(cdev, fops);
 	return cxlmd;
 
 err:
@@ -1332,15 +1342,16 @@ static struct cxl_memdev *cxl_memdev_alloc(struct cxl_mem *cxlm)
 	return ERR_PTR(rc);
 }
 
-static struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
-					      struct cxl_mem *cxlm)
+static struct cxl_memdev *
+devm_cxl_add_memdev(struct device *host, struct cxl_mem *cxlm,
+		    const struct cdevm_file_operations *cdevm_fops)
 {
 	struct cxl_memdev *cxlmd;
 	struct device *dev;
 	struct cdev *cdev;
 	int rc;
 
-	cxlmd = cxl_memdev_alloc(cxlm);
+	cxlmd = cxl_memdev_alloc(cxlm, &cdevm_fops->fops);
 	if (IS_ERR(cxlmd))
 		return cxlmd;
 
@@ -1370,7 +1381,7 @@ static struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
 	 * The cdev was briefly live, shutdown any ioctl operations that
 	 * saw that state.
 	 */
-	cxl_memdev_shutdown(cxlmd);
+	cdevm_fops->shutdown(dev);
 	put_device(dev);
 	return ERR_PTR(rc);
 }
@@ -1611,7 +1622,7 @@ static int cxl_mem_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	if (rc)
 		return rc;
 
-	cxlmd = devm_cxl_add_memdev(&pdev->dev, cxlm);
+	cxlmd = devm_cxl_add_memdev(&pdev->dev, cxlm, &cxl_memdev_fops);
 	if (IS_ERR(cxlmd))
 		return PTR_ERR(cxlmd);