[Xen-devel] [PATCH 1/7] xen-gntdev: Fix circular locking dependency

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxxx>
---
 drivers/xen/gntdev.c |   19 +++++++++----------
 1 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 35de6bb..387c5f1 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -608,23 +608,22 @@ 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) {
-               goto unlock_out;
-               if (debug)
-                       printk("%s: find_grant_ptes() failure.\n", 
__FUNCTION__);
-       }
+       if (err)
+               return err;
 
        err = map_grant_pages(map);
-       if (err) {
-               goto unlock_out;
-               if (debug)
-                       printk("%s: map_grant_pages() failure.\n", 
__FUNCTION__);
-       }
+       if (err)
+               return err;
+
        map->is_mapped = 1;
 
+       return 0;
+
 unlock_out:
        spin_unlock(&priv->lock);
        return err;
-- 
1.7.2.3


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