drm/ttm: Import Linux commit ff7c60c580d9722f820d85c9c58ca55ecc1ee7c4
drm/ttm: Import Linux commit ff7c60c580d9722f820d85c9c58ca55ecc1ee7c4

Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Mon Jan 14 15:08:14 2013 +0100

    drm/ttm: fix fence locking in ttm_buffer_object_transfer, 2nd try

    This fixes up

    commit e8e89622ed361c46bf90ba4828e685a8b603f7e5
    Author: Daniel Vetter <daniel.vetter@ffwll.ch>
    Date:   Tue Dec 18 22:25:11 2012 +0100

        drm/ttm: fix fence locking in ttm_buffer_object_transfer

    which leaves behind a might_sleep in atomic context, since the
    fence_lock spinlock is held over a kmalloc(GFP_KERNEL) call. The fix
    is to revert the above commit and only take the lock where we need it,
    around the call to ->sync_obj_ref.

    v2: Fixup things noticed by Maarten Lankhorst:
    - Brown paper bag locking bug.
    - No need for kzalloc if we clear the entire thing on the next line.
    - check for bo->sync_obj (totally unlikely race, but still someone
      else could have snuck in) and clear fbo->sync_obj if it's cleared
      already.

    Reported-by: Dave Airlie <airlied@gmail.com>
    Cc: Jerome Glisse <jglisse@redhat.com>
    Cc: Maarten Lankhorst <maarten.lankhorst@canonical.com>
    Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
    Signed-off-by: Dave Airlie <airlied@redhat.com>

Approved by:	kib@

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