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    Subject[PATCH 3.13.y-ckt 07/57] xen/gntdevt: Fix race condition in gntdev_release()
    Date
    3.13.11-ckt27 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: =?UTF-8?q?Marek=20Marczykowski-G=C3=B3recki?=

    commit 30b03d05e07467b8c6ec683ea96b5bffcbcd3931 upstream.

    While gntdev_release() is called the MMU notifier is still registered
    and can traverse priv->maps list even if no pages are mapped (which is
    the case -- gntdev_release() is called after all). But
    gntdev_release() will clear that list, so make sure that only one of
    those things happens at the same time.

    Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
    Signed-off-by: David Vrabel <david.vrabel@citrix.com>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    drivers/xen/gntdev.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
    index 0b58069..37c34b8 100644
    --- a/drivers/xen/gntdev.c
    +++ b/drivers/xen/gntdev.c
    @@ -529,12 +529,14 @@ static int gntdev_release(struct inode *inode, struct file *flip)

    pr_debug("priv %p\n", priv);

    + mutex_lock(&priv->lock);
    while (!list_empty(&priv->maps)) {
    map = list_entry(priv->maps.next, struct grant_map, next);
    list_del(&map->next);
    gntdev_put_map(NULL /* already removed */, map);
    }
    WARN_ON(!list_empty(&priv->freeable_maps));
    + mutex_unlock(&priv->lock);

    if (use_ptemod)
    mmu_notifier_unregister(&priv->mn, priv->mm);
    --
    1.9.1


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