drm/i915: Store a permanent error in obj->mm.pages

drm/i915: Store a permanent error in obj->mm.pages

BugLink: http://bugs.launchpad.net/bugs/1685140
commit 0d9dc306e15b59bf50db87ebcb1e2248586d4733 upstream.

Once the object has been truncated, it is unrecoverable. To facilitate
detection of this state store the error in obj->mm.pages.

This is required for the next patch which should be applied to v4.10
(via stable), so we also need to mark this patch for backporting. In
that regard, let's consider this to be a fix/improvement too.

v2: Avoid dereferencing the ERR_PTR when freeing the object.

Fixes: 1233e2db199d ("drm/i915: Move object backing storage manipulation to its own locking")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170307132031.32461-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
(cherry picked from commit 4e5462ee843c883790e9609cf560d88960ea4227)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>