[mmotm:master 87/135] mm/list_lru.c:140:2: error: implicit declaration of function 'prefetchw'

[kbuild test robot <fengguang.wu@intel.com>]

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tree:   git://git.cmpxchg.org/linux-mmotm.git master
head:   8c7e96fa64e41f4571040f7fe9c279d0438ad172
commit: b45866989c31d4c38cbe7d788919e3e71721706f [87/135] mm/list_lru.c: prefetch neighboring list entries before acquiring lock
config: blackfin-allmodconfig (attached as .config)
compiler: bfin-uclinux-gcc (GCC) 6.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        git checkout b45866989c31d4c38cbe7d788919e3e71721706f
        # save the attached .config to linux build tree
        make.cross ARCH=blackfin 

All errors (new ones prefixed by >>):

   mm/list_lru.c: In function 'list_lru_del':
>> mm/list_lru.c:140:2: error: implicit declaration of function 'prefetchw' [-Werror=implicit-function-declaration]
     prefetchw(item->prev);
     ^~~~~~~~~
   cc1: some warnings being treated as errors

vim +/prefetchw +140 mm/list_lru.c

   128	
   129	bool list_lru_del(struct list_lru *lru, struct list_head *item)
   130	{
   131		int nid = page_to_nid(virt_to_page(item));
   132		struct list_lru_node *nlru = &lru->node[nid];
   133		struct list_lru_one *l;
   134	
   135		/*
   136		 * Prefetch the neighboring list entries to reduce lock hold time.
   137		 */
   138		if (unlikely(list_empty(item)))
   139			return false;
 > 140		prefetchw(item->prev);
   141		prefetchw(item->next);
   142	
   143		spin_lock(&nlru->lock);
   144		if (likely(!list_empty(item))) {
   145			l = list_lru_from_kmem(nlru, item);
   146			list_del_init(item);
   147			l->nr_items--;
   148			nlru->nr_items--;
   149			spin_unlock(&nlru->lock);
   150			return true;
   151		}
   152		spin_unlock(&nlru->lock);
   153		return false;
   154	}
   155	EXPORT_SYMBOL_GPL(list_lru_del);
   156	

---
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