drm: fix up mmap locking in preparation for ttm changes

This change is needed to protect againt disappearing maps which aren't common.
The map lists are protected using sturct_mutex but drm_mmap never locked it.
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/char/drm/drm_vm.c

@@ -413,7 +413,7 @@ static struct vm_operations_struct drm_vm_sg_ops = {
  * Create a new drm_vma_entry structure as the \p vma private data entry and
  * add it to drm_device::vmalist.
  */
-static void drm_vm_open(struct vm_area_struct *vma)
+static void drm_vm_open_locked(struct vm_area_struct *vma)
 {
 	drm_file_t *priv = vma->vm_file->private_data;
 	drm_device_t *dev = priv->head->dev;
@@ -425,15 +425,23 @@ static void drm_vm_open(struct vm_area_struct *vma)
 
 	vma_entry = drm_alloc(sizeof(*vma_entry), DRM_MEM_VMAS);
 	if (vma_entry) {
-		mutex_lock(&dev->struct_mutex);
 		vma_entry->vma = vma;
 		vma_entry->next = dev->vmalist;
 		vma_entry->pid = current->pid;
 		dev->vmalist = vma_entry;
-		mutex_unlock(&dev->struct_mutex);
 	}
 }
 
+static void drm_vm_open(struct vm_area_struct *vma)
+{
+	drm_file_t *priv = vma->vm_file->private_data;
+	drm_device_t *dev = priv->head->dev;
+
+	mutex_lock(&dev->struct_mutex);
+	drm_vm_open_locked(vma);
+	mutex_unlock(&dev->struct_mutex);
+}
+
 /**
  * \c close method for all virtual memory types.
  *
@@ -484,7 +492,6 @@ static int drm_mmap_dma(struct file *filp, struct vm_area_struct *vma)
 	drm_device_dma_t *dma;
 	unsigned long length = vma->vm_end - vma->vm_start;
 
-	lock_kernel();
 	dev = priv->head->dev;
 	dma = dev->dma;
 	DRM_DEBUG("start = 0x%lx, end = 0x%lx, page offset = 0x%lx\n",
@@ -492,10 +499,8 @@ static int drm_mmap_dma(struct file *filp, struct vm_area_struct *vma)
 
 	/* Length must match exact page count */
 	if (!dma || (length >> PAGE_SHIFT) != dma->page_count) {
-		unlock_kernel();
 		return -EINVAL;
 	}
-	unlock_kernel();
 
 	if (!capable(CAP_SYS_ADMIN) &&
 	    (dma->flags & _DRM_DMA_USE_PCI_RO)) {
@@ -518,7 +523,7 @@ static int drm_mmap_dma(struct file *filp, struct vm_area_struct *vma)
 	vma->vm_flags |= VM_RESERVED;	/* Don't swap */
 
 	vma->vm_file = filp;	/* Needed for drm_vm_open() */
-	drm_vm_open(vma);
+	drm_vm_open_locked(vma);
 	return 0;
 }
 
@@ -553,7 +558,7 @@ EXPORT_SYMBOL(drm_core_get_reg_ofs);
  * according to the mapping type and remaps the pages. Finally sets the file
  * pointer and calls vm_open().
  */
-int drm_mmap(struct file *filp, struct vm_area_struct *vma)
+static int drm_mmap_locked(struct file *filp, struct vm_area_struct *vma)
 {
 	drm_file_t *priv = filp->private_data;
 	drm_device_t *dev = priv->head->dev;
@@ -667,8 +672,20 @@ int drm_mmap(struct file *filp, struct vm_area_struct *vma)
 	vma->vm_flags |= VM_RESERVED;	/* Don't swap */
 
 	vma->vm_file = filp;	/* Needed for drm_vm_open() */
-	drm_vm_open(vma);
+	drm_vm_open_locked(vma);
 	return 0;
 }
 
+int drm_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	drm_file_t *priv = filp->private_data;
+	drm_device_t *dev = priv->head->dev;
+	int ret;
+
+	mutex_lock(&dev->struct_mutex);
+	ret = drm_mmap_locked(filp, vma);
+	mutex_unlock(&dev->struct_mutex);
+
+	return ret;
+}
 EXPORT_SYMBOL(drm_mmap);