unused_nodes modification needs to be protected by unused_lock spinlock.
Here is an example of an usage where there is no such protection without
this patch.
Process 1: 1-drm_mm_pre_get(this function modify unused_nodes list)
2-spin_lock(spinlock protecting mm struct)
3-drm_mm_put_block(this function might modify unused_nodes
list but doesn't protect modification with unused_lock)
4-spin_unlock(spinlock protecting mm struct)
Process2: 1-drm_mm_pre_get(this function modify unused_nodes list)
At this point Process1 & Process2 might both be doing modification to
unused_nodes list. This patch add unused_lock protection into
drm_mm_put_block to avoid such issue.
Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
a698cf34ea