FROMLIST: mm: fix incorrect vbq reference in purge_fragmented_block

The function xa_for_each() in __vm_unmap_aliases()
traversal all vbs. But the vb from xarry may not be
on the corresponding CPU vmap_block_queue.
Consequently, purge_fragmented_block() might use
wrong vbq->lock to protect the free list,
and new_vmap_block() / purge_fragmented_block() may
perform concurrent operations on the free list.

Bug: 346658600
Link: https://lore.kernel.org/all/CAGWkznE-


HcYBia2HDcHt6trM9oeJ2x6KdyFzR3Jd_-L5HyPxSA@mail.gmail.com/

Change-Id: I1db9603f9c9892b36cf3b5c1ed5d961dec6816d5
Signed-off-by: Haonan Wang <haonan.wang@unisoc.com>