mm/damon/paddr: fix missing folio_put()

damon_get_folio() would always increase folio _refcount and
folio_isolate_lru() would increase folio _refcount if the folio's lru flag
is set.

If an unevictable folio isolated successfully, there will be two more
_refcount. The one from folio_isolate_lru() will be decreased in
folio_puback_lru(), but the other one from damon_get_folio() will be left
behind. This causes a pin page.

Whatever the case, the _refcount from damon_get_folio() should be
decreased.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 57223ac29584 ("mm/damon/paddr: support the pageout scheme")
Signed-off-by: andrew.yang <[e-mail]>
Reviewed-by: SeongJae Park <[e-mail]>
Cc: <[e-mail]> [5.16.x]
Signed-off-by: Andrew Morton <[e-mail]>

mm/damon/paddr.c

···
 			folio_put(folio);
 			continue;
 		}
-		if (folio_test_unevictable(folio)) {
+		if (folio_test_unevictable(folio))
 			folio_putback_lru(folio);
-		} else {
+		else
 			list_add(&folio->lru, &folio_list);
-			folio_put(folio);
-		}
+		folio_put(folio);
 	}
 	applied = reclaim_pages(&folio_list);
 	cond_resched();