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>

1 files changed, 11 insertions, 10 deletions

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 21eddd9e0f26..073788e50e4b 100644
--- 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;
 }