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>

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index a2ea5335e152fb9cd4736a27a57d4b7f4e82b402..aba76d437ea81307a9547fd89b0f60dc6f4b3b71 100644 (file)
--- 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;