Q: Given the following code slice:
```
1 static inline void __free_pages(struct page *page, unsigned int order)
2 {
3 	if (pcp_allowed_order(order))		/* Via pcp? */
4 		free_unref_page(page, order);
5 	else
6 		__free_pages_ok(page, order, FPI_NONE);
7 }
8 static inline void might_sleep(void)
9 {
10 	BUG_ON(preempt_disable_count);
11 }
12 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
13 {
14 	mutex_lock(&ring_info->ring_buffer_mutex);
15 	vunmap(ring_info->ring_buffer);
16 	ring_info->ring_buffer = NULL;
17 	mutex_unlock(&ring_info->ring_buffer_mutex);
18 
19 	kfree(ring_info->pkt_buffer);
20 	ring_info->pkt_buffer = NULL;
21 	ring_info->pkt_buffer_size = 0;
22 }
23 static inline int page_ref_dec_and_test(struct page *page)
24 {
25 	int ret = atomic_dec_and_test(&page->_refcount);
26 
27 	if (page_ref_tracepoint_active(page_ref_mod_and_test))
28 		__page_ref_mod_and_test(page, -1, ret);
29 	return ret;
30 }
31 void __sched mutex_lock(struct mutex *lock)
32 {
33 	might_sleep();
34 
35 	if (!__mutex_trylock_fast(lock))
36 		__mutex_lock_slowpath(lock);
37 }
38 static inline bool has_isolate_pageblock(struct zone *zone)
39 {
40 	return zone->nr_isolate_pageblock;
41 }
42 static void free_pcppages_bulk(struct zone *zone, int count,
43 					struct per_cpu_pages *pcp,
44 					int pindex)
45 {
46 	unsigned long flags;
47 	int min_pindex = 0;
48 	int max_pindex = NR_PCP_LISTS - 1;
49 	unsigned int order;
50 	bool isolated_pageblocks;
51 	struct page *page;
52 
53 	/*
54 	 * Ensure proper count is passed which otherwise would stuck in the
55 	 * below while (list_empty(list)) loop.
56 	 */
57 	count = min(pcp->count, count);
58 
59 	/* Ensure requested pindex is drained first. */
60 	pindex = pindex - 1;
61 
62 	spin_lock_irqsave(&zone->lock, flags);
63 	isolated_pageblocks = has_isolate_pageblock(zone);
64 
65 	while (count > 0) {
66 		struct list_head *list;
67 		int nr_pages;
68 
69 		/* Remove pages from lists in a round-robin fashion. */
70 		do {
71 			if (++pindex > max_pindex)
72 				pindex = min_pindex;
73 			list = &pcp->lists[pindex];
74 			if (!list_empty(list))
75 				break;
76 
77 			if (pindex == max_pindex)
78 				max_pindex--;
79 			if (pindex == min_pindex)
80 				min_pindex++;
81 		} while (1);
82 
83 		order = pindex_to_order(pindex);
84 		nr_pages = 1 << order;
85 		do {
86 			int mt;
87 
88 			page = list_last_entry(list, struct page, pcp_list);
89 			mt = get_pcppage_migratetype(page);
90 
91 			/* must delete to avoid corrupting pcp list */
92 			list_del(&page->pcp_list);
93 			count -= nr_pages;
94 			pcp->count -= nr_pages;
95 
96 			if (bulkfree_pcp_prepare(page))
97 				continue;
98 
99 			/* MIGRATE_ISOLATE page should not go to pcplists */
100 			VM_BUG_ON_PAGE(is_migrate_isolate(mt), page);
101 			/* Pageblock could have been isolated meanwhile */
102 			if (unlikely(isolated_pageblocks))
103 				mt = get_pageblock_migratetype(page);
104 
105 			__free_one_page(page, page_to_pfn(page), zone, order, mt, FPI_NONE);
106 			trace_mm_page_pcpu_drain(page, order, mt);
107 		} while (count > 0 && !list_empty(list));
108 	}
109 
110 	spin_unlock_irqrestore(&zone->lock, flags);
111 }
112 static bool free_pcp_prepare(struct page *page, unsigned int order)
113 {
114 	return free_pages_prepare(page, order, true, FPI_NONE);
115 }
116 static bool free_unref_page_prepare(struct page *page, unsigned long pfn,
117 							unsigned int order)
118 {
119 	int migratetype;
120 
121 	if (!free_pcp_prepare(page, order))
122 		return false;
123 
124 	migratetype = get_pfnblock_migratetype(page, pfn);
125 	set_pcppage_migratetype(page, migratetype);
126 	return true;
127 }
128 static __always_inline int page_is_fake_head(struct page *page)
129 {
130 	return page_fixed_fake_head(page) != page;
131 }
132 void __sched mutex_unlock(struct mutex *lock)
133 {
134 	mutex_release(&lock->dep_map, _RET_IP_);
135 	__rt_mutex_unlock(&lock->rtmutex);
136 }
137 static int nr_pcp_free(struct per_cpu_pages *pcp, int high, int batch,
138 		       bool free_high)
139 {
140 	int min_nr_free, max_nr_free;
141 
142 	/* Free everything if batch freeing high-order pages. */
143 	if (unlikely(free_high))
144 		return pcp->count;
145 
146 	/* Check for PCP disabled or boot pageset */
147 	if (unlikely(high < batch))
148 		return 1;
149 
150 	/* Leave at least pcp->batch pages on the list */
151 	min_nr_free = batch;
152 	max_nr_free = high - batch;
153 
154 	/*
155 	 * Double the number of pages freed each time there is subsequent
156 	 * freeing of pages without any allocation.
157 	 */
158 	batch <<= pcp->free_factor;
159 	if (batch < max_nr_free)
160 		pcp->free_factor++;
161 	batch = clamp(batch, min_nr_free, max_nr_free);
162 
163 	return batch;
164 }
165 static inline void set_pcppage_migratetype(struct page *page, int migratetype)
166 {
167 	page->index = migratetype;
168 }
169 static __always_inline int PageHead(struct page *page)
170 {
171 	PF_POISONED_CHECK(page);
172 	return test_bit(PG_head, &page->flags) && !page_is_fake_head(page);
173 }
174 static __always_inline int get_pfnblock_migratetype(const struct page *page,
175 					unsigned long pfn)
176 {
177 	return __get_pfnblock_flags_mask(page, pfn, MIGRATETYPE_MASK);
178 }
179 void vunmap(const void *addr)
180 {
181 	BUG();
182 }
183 static void __free_pages_ok(struct page *page, unsigned int order,
184 			    fpi_t fpi_flags)
185 {
186 	unsigned long flags;
187 	int migratetype;
188 	unsigned long pfn = page_to_pfn(page);
189 	struct zone *zone = page_zone(page);
190 
191 	if (!free_pages_prepare(page, order, true, fpi_flags))
192 		return;
193 
194 	migratetype = get_pfnblock_migratetype(page, pfn);
195 
196 	spin_lock_irqsave(&zone->lock, flags);
197 	if (unlikely(has_isolate_pageblock(zone) ||
198 		is_migrate_isolate(migratetype))) {
199 		migratetype = get_pfnblock_migratetype(page, pfn);
200 	}
201 	__free_one_page(page, pfn, zone, order, migratetype, fpi_flags);
202 	spin_unlock_irqrestore(&zone->lock, flags);
203 
204 	__count_vm_events(PGFREE, 1 << order);
205 }
206 static inline enum zone_type page_zonenum(const struct page *page)
207 {
208 	ASSERT_EXCLUSIVE_BITS(page->flags, ZONES_MASK << ZONES_PGSHIFT);
209 	return (page->flags >> ZONES_PGSHIFT) & ZONES_MASK;
210 }
211 static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock)
212 {
213 	if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
214 		return;
215 
216 	rt_mutex_slowunlock(lock);
217 }
218 static inline int page_ref_count(const struct page *page)
219 {
220 	return atomic_read(&page->_refcount);
221 }
222 static void free_unref_page_commit(struct zone *zone, struct per_cpu_pages *pcp,
223 				   struct page *page, int migratetype,
224 				   unsigned int order)
225 {
226 	int high;
227 	int pindex;
228 	bool free_high;
229 
230 	__count_vm_events(PGFREE, 1 << order);
231 	pindex = order_to_pindex(migratetype, order);
232 	list_add(&page->pcp_list, &pcp->lists[pindex]);
233 	pcp->count += 1 << order;
234 
235 	/*
236 	 * As high-order pages other than THP's stored on PCP can contribute
237 	 * to fragmentation, limit the number stored when PCP is heavily
238 	 * freeing without allocation. The remainder after bulk freeing
239 	 * stops will be drained from vmstat refresh context.
240 	 */
241 	free_high = (pcp->free_factor && order && order <= PAGE_ALLOC_COSTLY_ORDER);
242 
243 	high = nr_pcp_high(pcp, zone, free_high);
244 	if (pcp->count >= high) {
245 		int batch = READ_ONCE(pcp->batch);
246 
247 		free_pcppages_bulk(zone, nr_pcp_free(pcp, high, batch, free_high), pcp, pindex);
248 	}
249 }
250 static int nr_pcp_high(struct per_cpu_pages *pcp, struct zone *zone,
251 		       bool free_high)
252 {
253 	int high = READ_ONCE(pcp->high);
254 
255 	if (unlikely(!high || free_high))
256 		return 0;
257 
258 	if (!test_bit(ZONE_RECLAIM_ACTIVE, &zone->flags))
259 		return high;
260 
261 	/*
262 	 * If reclaim is active, limit the number of pages that can be
263 	 * stored on pcp lists
264 	 */
265 	return min(READ_ONCE(pcp->batch) << 2, high);
266 }
267 static inline void __free_one_page(struct page *page,
268 		unsigned long pfn,
269 		struct zone *zone, unsigned int order,
270 		int migratetype, fpi_t fpi_flags)
271 {
272 	struct capture_control *capc = task_capc(zone);
273 	unsigned long buddy_pfn = 0;
274 	unsigned long combined_pfn;
275 	struct page *buddy;
276 	bool to_tail;
277 
278 	VM_BUG_ON(!zone_is_initialized(zone));
279 	VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP, page);
280 
281 	VM_BUG_ON(migratetype == -1);
282 	if (likely(!is_migrate_isolate(migratetype)))
283 		__mod_zone_freepage_state(zone, 1 << order, migratetype);
284 
285 	VM_BUG_ON_PAGE(pfn & ((1 << order) - 1), page);
286 	VM_BUG_ON_PAGE(bad_range(zone, page), page);
287 
288 	while (order < MAX_ORDER - 1) {
289 		if (compaction_capture(capc, page, order, migratetype)) {
290 			__mod_zone_freepage_state(zone, -(1 << order),
291 								migratetype);
292 			return;
293 		}
294 
295 		buddy = find_buddy_page_pfn(page, pfn, order, &buddy_pfn);
296 		if (!buddy)
297 			goto done_merging;
298 
299 		if (unlikely(order >= pageblock_order)) {
300 			/*
301 			 * We want to prevent merge between freepages on pageblock
302 			 * without fallbacks and normal pageblock. Without this,
303 			 * pageblock isolation could cause incorrect freepage or CMA
304 			 * accounting or HIGHATOMIC accounting.
305 			 */
306 			int buddy_mt = get_pageblock_migratetype(buddy);
307 
308 			if (migratetype != buddy_mt
309 					&& (!migratetype_is_mergeable(migratetype) ||
310 						!migratetype_is_mergeable(buddy_mt)))
311 				goto done_merging;
312 		}
313 
314 		/*
315 		 * Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page,
316 		 * merge with it and move up one order.
317 		 */
318 		if (page_is_guard(buddy))
319 			clear_page_guard(zone, buddy, order, migratetype);
320 		else
321 			del_page_from_free_list(buddy, zone, order);
322 		combined_pfn = buddy_pfn & pfn;
323 		page = page + (combined_pfn - pfn);
324 		pfn = combined_pfn;
325 		order++;
326 	}
327 
328 done_merging:
329 	set_buddy_order(page, order);
330 
331 	if (fpi_flags & FPI_TO_TAIL)
332 		to_tail = true;
333 	else if (is_shuffle_order(order))
334 		to_tail = shuffle_pick_tail();
335 	else
336 		to_tail = buddy_merge_likely(pfn, buddy_pfn, page, order);
337 
338 	if (to_tail)
339 		add_to_free_list_tail(page, zone, order, migratetype);
340 	else
341 		add_to_free_list(page, zone, order, migratetype);
342 
343 	/* Notify page reporting subsystem of freed page */
344 	if (!(fpi_flags & FPI_SKIP_REPORT_NOTIFY))
345 		page_reporting_notify_free(order);
346 }
347 int page_to_nid(const struct page *page)
348 {
349 	return section_to_node_table[page_to_section(page)];
350 }
351 void free_unref_page(struct page *page, unsigned int order)
352 {
353 	unsigned long __maybe_unused UP_flags;
354 	struct per_cpu_pages *pcp;
355 	struct zone *zone;
356 	unsigned long pfn = page_to_pfn(page);
357 	int migratetype, pcpmigratetype;
358 
359 	if (!free_unref_page_prepare(page, pfn, order))
360 		return;
361 
362 	/*
363 	 * We only track unmovable, reclaimable and movable on pcp lists.
364 	 * Place ISOLATE pages on the isolated list because they are being
365 	 * offlined but treat HIGHATOMIC and CMA as movable pages so we can
366 	 * get those areas back if necessary. Otherwise, we may have to free
367 	 * excessively into the page allocator
368 	 */
369 	migratetype = pcpmigratetype = get_pcppage_migratetype(page);
370 	if (unlikely(migratetype >= MIGRATE_PCPTYPES)) {
371 		if (unlikely(is_migrate_isolate(migratetype))) {
372 			free_one_page(page_zone(page), page, pfn, order, migratetype, FPI_NONE);
373 			return;
374 		}
375 		pcpmigratetype = MIGRATE_MOVABLE;
376 	}
377 
378 	zone = page_zone(page);
379 	pcp_trylock_prepare(UP_flags);
380 	pcp = pcp_spin_trylock(zone->per_cpu_pageset);
381 	if (pcp) {
382 		free_unref_page_commit(zone, pcp, page, pcpmigratetype, order);
383 		pcp_spin_unlock(pcp);
384 	} else {
385 		free_one_page(zone, page, pfn, order, migratetype, FPI_NONE);
386 	}
387 	pcp_trylock_finish(UP_flags);
388 }
389 static inline void kfree(void *p)
390 {
391 	if (p >= __kfree_ignore_start && p < __kfree_ignore_end)
392 		return;
393 	free(p);
394 }
395 void __free_pages(struct page *page, unsigned int order)
396 {
397 	/* get PageHead before we drop reference */
398 	int head = PageHead(page);
399 
400 	if (put_page_testzero(page))
401 		free_the_page(page, order);
402 	else if (!head)
403 		while (order-- > 0)
404 			free_the_page(page + (1 << order), order);
405 }
406 static inline int put_page_testzero(struct page *page)
407 {
408 	VM_BUG_ON_PAGE(page_ref_count(page) == 0, page);
409 	return page_ref_dec_and_test(page);
410 }
411 static inline void spin_unlock_irqrestore(spinlock_t *lock, unsigned long f)
412 {
413 	spin_unlock(lock);
414 }
415 static noinline void __sched
416 __mutex_lock_slowpath(struct mutex *lock)
417 {
418 	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
419 }
420 out:		/* free if the candidate is valid */
421 		if (!IS_ERR(candidate))
422 			erofs_put_metabuf(target);
423 		return de;
424 	}
425 	return candidate;
426 }
427 static inline void spin_lock_irqsave(spinlock_t *lock, unsigned long f)
428 {
429 	spin_lock(lock);
430 }
431 static inline struct zone *page_zone(const struct page *page)
432 {
433 	return &NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)];
434 }
435 static inline void free_the_page(struct page *page, unsigned int order)
436 {
437 	if (pcp_allowed_order(order))		/* Via pcp? */
438 		free_unref_page(page, order);
439 	else
440 		__free_pages_ok(page, order, FPI_NONE);
441 }
442 void vmbus_free_ring(struct vmbus_channel *channel)
443 {
444         hv_ringbuffer_cleanup(&channel->outbound);
445         hv_ringbuffer_cleanup(&channel->inbound);
446 
447         if (channel->ringbuffer_page) {
448                 __free_pages(channel->ringbuffer_page,
449                              get_order(channel->ringbuffer_pagecount
450                                        << PAGE_SHIFT));
451                 channel->ringbuffer_page = NULL;
452         }
453 }
454 static void free_one_page(struct zone *zone,
455 				struct page *page, unsigned long pfn,
456 				unsigned int order,
457 				int migratetype, fpi_t fpi_flags)
458 {
459 	unsigned long flags;
460 
461 	spin_lock_irqsave(&zone->lock, flags);
462 	if (unlikely(has_isolate_pageblock(zone) ||
463 		is_migrate_isolate(migratetype))) {
464 		migratetype = get_pfnblock_migratetype(page, pfn);
465 	}
466 	__free_one_page(page, pfn, zone, order, migratetype, fpi_flags);
467 	spin_unlock_irqrestore(&zone->lock, flags);
468 }
469 static inline bool is_migrate_isolate(int migratetype)
470 {
471 	return migratetype == MIGRATE_ISOLATE;
472 }
473 static inline int get_pcppage_migratetype(struct page *page)
474 {
475 	return page->index;
476 }
477 static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
478 {
479 	unsigned long curr = (unsigned long)current;
480 	unsigned long zero = 0UL;
481 
482 	if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))
483 		return true;
484 
485 	return false;
486 }
487 static inline void list_add(struct list_head *new, struct list_head *head)
488 {
489 	__list_add(new, head, head->next);
490 }
491 static inline void __count_vm_events(enum vm_event_item item, long delta)
492 {
493 	raw_cpu_add(vm_event_states.event[item], delta);
494 }
```
which has a vulnerability among CWE-401 and among lines:
```
4 		free_unref_page(page, order);
```
Please generate five possible patches for the vulnerability.