!678 backport some bug fix for page pool

Merge Pull Request from: @svishen 
 
backport the patch community has solved a page_pool problem.

issue:
https://gitee.com/openeuler/kernel/issues/I718LV 
 
Link:https://gitee.com/openeuler/kernel/pulls/678 

Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com> 

net/core/skbuff.c

@@ -5261,18 +5261,18 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
 	if (skb_cloned(to))
 		return false;
 
-	/* In general, avoid mixing slab allocated and page_pool allocated
-	 * pages within the same SKB. However when @to is not pp_recycle and
-	 * @from is cloned, we can transition frag pages from page_pool to
-	 * reference counted.
-	 *
-	 * On the other hand, don't allow coalescing two pp_recycle SKBs if
-	 * @from is cloned, in case the SKB is using page_pool fragment
+	/* In general, avoid mixing page_pool and non-page_pool allocated
+	 * pages within the same SKB. Additionally avoid dealing with clones
+	 * with page_pool pages, in case the SKB is using page_pool fragment
 	 * references (PP_FLAG_PAGE_FRAG). Since we only take full page
 	 * references for cloned SKBs at the moment that would result in
 	 * inconsistent reference counts.
+	 * In theory we could take full references if @from is cloned and
+	 * !@to->pp_recycle but its tricky (due to potential race with
+	 * the clone disappearing) and rare, so not worth dealing with.
 	 */
-	if (to->pp_recycle != (from->pp_recycle && !skb_cloned(from)))
+	if (to->pp_recycle != from->pp_recycle ||
+	    (from->pp_recycle && skb_cloned(from)))
 		return false;
 
 	if (len <= skb_tailroom(to)) {