We may encounter duplicate entry in the zswap_store():

1. swap slot that freed to per-cpu swap cache, doesn't invalidate
   the zswap entry, then got reused. This has been fixed.

2. !exclusive load mode, swapin folio will leave its zswap entry
   on the tree, then swapout again. This has been removed.

3. one folio can be dirtied again after zswap_store(), so need to
   zswap_store() again. This should be handled correctly.

So we must invalidate the old duplicate entry before inserting the
new one, which actually doesn't have to be done at the beginning
of zswap_store().

The good point is that we don't need to lock the tree twice in the normal
store success path.  And cleanup the loop as we are here.

Note we still need to invalidate the old duplicate entry when store failed
or zswap is disabled , otherwise the new data in swapfile could be
overwrite by the old data in zswap pool when lru writeback.

Link: https://lkml.kernel.org/r/20240209044112.3883835-1-chengming.zhou@linux.devSigned-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Chris Li <chrisl@kernel.org>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>