genirq/msi: Add mutex for MSI list protection

For upcoming runtime extensions of MSI-X interrupts it's required to
protect the MSI descriptor list. Add a mutex to struct msi_device_data and
provide lock/unlock functions.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20211206210747.708877269@linutronix.de

include/linux/msi.h

@@ -3,6 +3,7 @@
 #define LINUX_MSI_H
 
 #include <linux/cpumask.h>
+#include <linux/mutex.h>
 #include <linux/list.h>
 #include <asm/msi.h>
 
@@ -145,17 +146,21 @@ struct msi_desc {
  * @attrs:		Pointer to the sysfs attribute group
  * @platform_data:	Platform-MSI specific data
  * @list:		List of MSI descriptors associated to the device
+ * @mutex:		Mutex protecting the MSI list
  */
 struct msi_device_data {
 	unsigned long			properties;
 	const struct attribute_group    **attrs;
 	struct platform_msi_priv_data	*platform_data;
 	struct list_head		list;
+	struct mutex			mutex;
 };
 
 int msi_setup_device_data(struct device *dev);
 
 unsigned int msi_get_virq(struct device *dev, unsigned int index);
+void msi_lock_descs(struct device *dev);
+void msi_unlock_descs(struct device *dev);
 
 /* Helpers to hide struct msi_desc implementation details */
 #define msi_desc_to_dev(desc)		((desc)->dev)

kernel/irq/msi.c

@@ -103,11 +103,32 @@ int msi_setup_device_data(struct device *dev)
 		return -ENOMEM;
 
 	INIT_LIST_HEAD(&md->list);
+	mutex_init(&md->mutex);
 	dev->msi.data = md;
 	devres_add(dev, md);
 	return 0;
 }
 
+/**
+ * msi_lock_descs - Lock the MSI descriptor storage of a device
+ * @dev:	Device to operate on
+ */
+void msi_lock_descs(struct device *dev)
+{
+	mutex_lock(&dev->msi.data->mutex);
+}
+EXPORT_SYMBOL_GPL(msi_lock_descs);
+
+/**
+ * msi_unlock_descs - Unlock the MSI descriptor storage of a device
+ * @dev:	Device to operate on
+ */
+void msi_unlock_descs(struct device *dev)
+{
+	mutex_unlock(&dev->msi.data->mutex);
+}
+EXPORT_SYMBOL_GPL(msi_unlock_descs);
+
 /**
  * msi_get_virq - Return Linux interrupt number of a MSI interrupt
  * @dev:	Device to operate on