xen/gntdev: Fix circular locking dependency

apply_to_page_range will acquire PTE lock while priv->lock is held,
and mn_invl_range_start tries to acquire priv->lock with PTE already
held.  Fix by not holding priv->lock during the entire map operation.
This is safe because map->vma is set nonzero while the lock is held,
which will cause subsequent maps to fail and will cause the unmap
ioctl (and other users of gntdev_del_map) to return -EBUSY until the
area is unmapped. It is similarly impossible for gntdev_vma_close to
be called while the vma is still being created.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index a2ea5335e152..aba76d437ea8 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -575,21 +575,26 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
         if (!(vma->vm_flags & VM_WRITE))
                 map->flags |= GNTMAP_readonly;
 
+        spin_unlock(&priv->lock);
+
         err = apply_to_page_range(vma->vm_mm, vma->vm_start,
                                   vma->vm_end - vma->vm_start,
                                   find_grant_ptes, map);
         if (err) {
                 printk(KERN_WARNING "find_grant_ptes() failure.\n");
-                goto unlock_out;
+                return err;
         }
 
         err = map_grant_pages(map);
         if (err) {
                 printk(KERN_WARNING "map_grant_pages() failure.\n");
-                goto unlock_out;
+                return err;
         }
+
         map->is_mapped = 1;
 
+        return 0;
+
 unlock_out:
         spin_unlock(&priv->lock);
         return err;