There were two cases where dm_cell_visit_release() was being called,
which removes the cell from the prison's rbtree, but the callers didn't
also return the cell to the mempool. Fix this by having them call
free_prison_cell().
This leak manifested as the 'kmalloc-96' slab growing until OOM.
Fixes: 651f5fa2a3 ("dm cache: defer whole cells")
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # 4.1+
Joe Thornber
9153df7405