mm/z3fold: remove buggy use of stale list for allocation

Currently if z3fold couldn't find an unbuddied page it would first try to
pull a page off the stale list.  But this approach is problematic.  If
init z3fold page fails later, the page should be freed via
free_z3fold_page to clean up the relevant resource instead of using
__free_page directly.  And if page is successfully reused, it will BUG_ON
later in __SetPageMovable because it's already non-lru movable page, i.e. 
PAGE_MAPPING_MOVABLE is already set in page->mapping.  In order to fix all
of these issues, we can simply remove the buggy use of stale list for
allocation because can_sleep should always be false and we never really
hit the reusing code path now.

Link: https://lkml.kernel.org/r/20220429064051.61552-4-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/z3fold.c

@@ -1102,28 +1102,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
 		bud = FIRST;
 	}
 
-	page = NULL;
-	if (can_sleep) {
-		spin_lock(&pool->stale_lock);
-		zhdr = list_first_entry_or_null(&pool->stale,
-						struct z3fold_header, buddy);
-		/*
-		 * Before allocating a page, let's see if we can take one from
-		 * the stale pages list. cancel_work_sync() can sleep so we
-		 * limit this case to the contexts where we can sleep
-		 */
-		if (zhdr) {
-			list_del(&zhdr->buddy);
-			spin_unlock(&pool->stale_lock);
-			cancel_work_sync(&zhdr->work);
-			page = virt_to_page(zhdr);
-		} else {
-			spin_unlock(&pool->stale_lock);
-		}
-	}
-	if (!page)
-		page = alloc_page(gfp);
-
+	page = alloc_page(gfp);
 	if (!page)
 		return -ENOMEM;