vfio: Convert container->group_lock to rwsem

All current users are writers, maintaining current mutual exclusion.
This lets us add read users next.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 21eddd9e0f2610ffbf80ca9a90584f8951fb4fc4..073788e50e4b331f62036cfba09abdaf13d6fdf3 100644 (file)
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -24,6 +24,7 @@
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/rwsem.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/string.h>
@@ -57,7 +58,7 @@ struct vfio_iommu_driver {
 struct vfio_container {
        struct kref                     kref;
        struct list_head                group_list;
-       struct mutex                    group_lock;
+       struct rw_semaphore             group_lock;
        struct vfio_iommu_driver        *iommu_driver;
        void                            *iommu_data;
 };
@@ -738,7 +739,7 @@ static long vfio_ioctl_check_extension(struct vfio_container *container,
        return ret;
 }
 
-/* hold container->group_lock */
+/* hold write lock on container->group_lock */
 static int __vfio_container_attach_groups(struct vfio_container *container,
                                          struct vfio_iommu_driver *driver,
                                          void *data)
@@ -769,7 +770,7 @@ static long vfio_ioctl_set_iommu(struct vfio_container *container,
        struct vfio_iommu_driver *driver;
        long ret = -ENODEV;
 
-       mutex_lock(&container->group_lock);
+       down_write(&container->group_lock);
 
        /*
         * The container is designed to be an unprivileged interface while
@@ -780,7 +781,7 @@ static long vfio_ioctl_set_iommu(struct vfio_container *container,
         * the container is deprivileged and returns to an unset state.
         */
        if (list_empty(&container->group_list) || container->iommu_driver) {
-               mutex_unlock(&container->group_lock);
+               up_write(&container->group_lock);
                return -EINVAL;
        }
 
@@ -827,7 +828,7 @@ static long vfio_ioctl_set_iommu(struct vfio_container *container,
 
        mutex_unlock(&vfio.iommu_drivers_lock);
 skip_drivers_unlock:
-       mutex_unlock(&container->group_lock);
+       up_write(&container->group_lock);
 
        return ret;
 }
@@ -882,7 +883,7 @@ static int vfio_fops_open(struct inode *inode, struct file *filep)
                return -ENOMEM;
 
        INIT_LIST_HEAD(&container->group_list);
-       mutex_init(&container->group_lock);
+       init_rwsem(&container->group_lock);
        kref_init(&container->kref);
 
        filep->private_data = container;
@@ -961,7 +962,7 @@ static void __vfio_group_unset_container(struct vfio_group *group)
        struct vfio_container *container = group->container;
        struct vfio_iommu_driver *driver;
 
-       mutex_lock(&container->group_lock);
+       down_write(&container->group_lock);
 
        driver = container->iommu_driver;
        if (driver)
@@ -979,7 +980,7 @@ static void __vfio_group_unset_container(struct vfio_group *group)
                container->iommu_data = NULL;
        }
 
-       mutex_unlock(&container->group_lock);
+       up_write(&container->group_lock);
 
        vfio_container_put(container);
 }
@@ -1039,7 +1040,7 @@ static int vfio_group_set_container(struct vfio_group *group, int container_fd)
        container = f.file->private_data;
        WARN_ON(!container); /* fget ensures we don't race vfio_release */
 
-       mutex_lock(&container->group_lock);
+       down_write(&container->group_lock);
 
        driver = container->iommu_driver;
        if (driver) {
@@ -1057,7 +1058,7 @@ static int vfio_group_set_container(struct vfio_group *group, int container_fd)
        atomic_inc(&group->container_users);
 
 unlock_out:
-       mutex_unlock(&container->group_lock);
+       up_write(&container->group_lock);
        fdput(f);
        return ret;
 }