Re: [PATCH] mm: check the return value of lookup_page_ext for all call sites

[Minchan Kim <minchan@kernel.org>]

On Thu, May 26, 2016 at 04:15:28PM -0700, Shi, Yang wrote:
> On 5/25/2016 5:37 PM, Minchan Kim wrote:
> >On Tue, May 24, 2016 at 11:58:11AM +0900, Minchan Kim wrote:
> >>On Mon, May 23, 2016 at 10:16:08AM -0700, Yang Shi wrote:
> >>>Per the discussion with Joonsoo Kim [1], we need check the return value of
> >>>lookup_page_ext() for all call sites since it might return NULL in some cases,
> >>>although it is unlikely, i.e. memory hotplug.
> >>>
> >>>Tested with ltp with "page_owner=0".
> >>>
> >>>[1] http://lkml.kernel.org/r/20160519002809.GA10245@js1304-P5Q-DELUXE
> >>>
> >>>Signed-off-by: Yang Shi <yang.shi@linaro.org>
> >>
> >>I didn't read code code in detail to see how page_ext memory space
> >>allocated in boot code and memory hotplug but to me, it's not good
> >>to check NULL whenever we calls lookup_page_ext.
> >>
> >>More dangerous thing is now page_ext is used by optionable feature(ie, not
> >>critical for system stability) but if we want to use page_ext as
> >>another important tool for the system in future,
> >>it could be a serious problem.
> >>
> >>Can we put some hooks of page_ext into memory-hotplug so guarantee
> >>that page_ext memory space is allocated with memmap space at the
> >>same time? IOW, once every PFN wakers find a page is valid, page_ext
> >>is valid, too so lookup_page_ext never returns NULL on valid page
> >>by design.
> >>
> >>I hope we consider this direction, too.
> >
> >Yang, Could you think about this?
> 
> Thanks a lot for the suggestion. Sorry for the late reply, I was
> busy on preparing patches. I do agree this is a direction we should
> look into, but I haven't got time to think about it deeper. I hope
> Joonsoo could chime in too since he is the original author for page
> extension.
> 
> >
> >Even, your patch was broken, I think.
> >It doesn't work with !CONFIG_DEBUG_VM && !CONFIG_PAGE_POISONING because
> >lookup_page_ext doesn't return NULL in that case.
> 
> Actually, I think the #ifdef should be removed if lookup_page_ext()
> is possible to return NULL. It sounds not make sense returning NULL
> only when DEBUG_VM is enabled. It should return NULL no matter what
> debug config is selected. If Joonsoo agrees with me I'm going to
> come up with a patch to fix it.

I don't know what lock protects race section->page_ext storing/tearing
during memory hotplug while random thread accesses pege_ext,
for example, kpageflags->page_is_idle.

Please consider that, too if you want to go with this approach.

> 
> Regards,
> Yang
> 
> >
> >>
> >>Thanks.
> >>
> >>>---
> >>> include/linux/page_idle.h | 43 ++++++++++++++++++++++++++++++++++++-------
> >>> mm/page_alloc.c           |  6 ++++++
> >>> mm/page_owner.c           | 27 +++++++++++++++++++++++++++
> >>> mm/page_poison.c          |  8 +++++++-
> >>> mm/vmstat.c               |  2 ++
> >>> 5 files changed, 78 insertions(+), 8 deletions(-)
> >>>
> >>>diff --git a/include/linux/page_idle.h b/include/linux/page_idle.h
> >>>index bf268fa..8f5d4ad 100644
> >>>--- a/include/linux/page_idle.h
> >>>+++ b/include/linux/page_idle.h
> >>>@@ -46,33 +46,62 @@ extern struct page_ext_operations page_idle_ops;
> >>>
> >>> static inline bool page_is_young(struct page *page)
> >>> {
> >>>-	return test_bit(PAGE_EXT_YOUNG, &lookup_page_ext(page)->flags);
> >>>+	struct page_ext *page_ext;
> >>>+	page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext)
> >>>+		return false;
> >>>+
> >>>+	return test_bit(PAGE_EXT_YOUNG, &page_ext->flags);
> >>> }
> >>>
> >>> static inline void set_page_young(struct page *page)
> >>> {
> >>>-	set_bit(PAGE_EXT_YOUNG, &lookup_page_ext(page)->flags);
> >>>+	struct page_ext *page_ext;
> >>>+	page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext)
> >>>+		return;
> >>>+
> >>>+	set_bit(PAGE_EXT_YOUNG, &page_ext->flags);
> >>> }
> >>>
> >>> static inline bool test_and_clear_page_young(struct page *page)
> >>> {
> >>>-	return test_and_clear_bit(PAGE_EXT_YOUNG,
> >>>-				  &lookup_page_ext(page)->flags);
> >>>+	struct page_ext *page_ext;
> >>>+	page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext)
> >>>+		return false;
> >>>+
> >>>+	return test_and_clear_bit(PAGE_EXT_YOUNG, &page_ext->flags);
> >>> }
> >>>
> >>> static inline bool page_is_idle(struct page *page)
> >>> {
> >>>-	return test_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
> >>>+	struct page_ext *page_ext;
> >>>+	page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext)
> >>>+		return false;
> >>>+
> >>>+	return test_bit(PAGE_EXT_IDLE, &page_ext->flags);
> >>> }
> >>>
> >>> static inline void set_page_idle(struct page *page)
> >>> {
> >>>-	set_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
> >>>+	struct page_ext *page_ext;
> >>>+	page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext)
> >>>+		return;
> >>>+
> >>>+	set_bit(PAGE_EXT_IDLE, &page_ext->flags);
> >>> }
> >>>
> >>> static inline void clear_page_idle(struct page *page)
> >>> {
> >>>-	clear_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
> >>>+	struct page_ext *page_ext;
> >>>+	page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext)
> >>>+		return;
> >>>+
> >>>+	clear_bit(PAGE_EXT_IDLE, &page_ext->flags);
> >>> }
> >>> #endif /* CONFIG_64BIT */
> >>>
> >>>diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >>>index f8f3bfc..d27e8b9 100644
> >>>--- a/mm/page_alloc.c
> >>>+++ b/mm/page_alloc.c
> >>>@@ -656,6 +656,9 @@ static inline void set_page_guard(struct zone *zone, struct page *page,
> >>> 		return;
> >>>
> >>> 	page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext))
> >>>+		return;
> >>>+
> >>> 	__set_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);
> >>>
> >>> 	INIT_LIST_HEAD(&page->lru);
> >>>@@ -673,6 +676,9 @@ static inline void clear_page_guard(struct zone *zone, struct page *page,
> >>> 		return;
> >>>
> >>> 	page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext))
> >>>+		return;
> >>>+
> >>> 	__clear_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);
> >>>
> >>> 	set_page_private(page, 0);
> >>>diff --git a/mm/page_owner.c b/mm/page_owner.c
> >>>index 792b56d..902e398 100644
> >>>--- a/mm/page_owner.c
> >>>+++ b/mm/page_owner.c
> >>>@@ -55,6 +55,8 @@ void __reset_page_owner(struct page *page, unsigned int order)
> >>>
> >>> 	for (i = 0; i < (1 << order); i++) {
> >>> 		page_ext = lookup_page_ext(page + i);
> >>>+		if (unlikely(!page_ext))
> >>>+			continue;
> >>> 		__clear_bit(PAGE_EXT_OWNER, &page_ext->flags);
> >>> 	}
> >>> }
> >>>@@ -62,6 +64,10 @@ void __reset_page_owner(struct page *page, unsigned int order)
> >>> void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask)
> >>> {
> >>> 	struct page_ext *page_ext = lookup_page_ext(page);
> >>>+
> >>>+	if (unlikely(!page_ext))
> >>>+		return;
> >>>+
> >>> 	struct stack_trace trace = {
> >>> 		.nr_entries = 0,
> >>> 		.max_entries = ARRAY_SIZE(page_ext->trace_entries),
> >>>@@ -82,6 +88,8 @@ void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask)
> >>> void __set_page_owner_migrate_reason(struct page *page, int reason)
> >>> {
> >>> 	struct page_ext *page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext))
> >>>+		return;
> >>>
> >>> 	page_ext->last_migrate_reason = reason;
> >>> }
> >>>@@ -89,6 +97,12 @@ void __set_page_owner_migrate_reason(struct page *page, int reason)
> >>> gfp_t __get_page_owner_gfp(struct page *page)
> >>> {
> >>> 	struct page_ext *page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext))
> >>>+		/*
> >>>+		 * The caller just returns 0 if no valid gfp
> >>>+		 * So return 0 here too.
> >>>+		 */
> >>>+		return 0;
> >>>
> >>> 	return page_ext->gfp_mask;
> >>> }
> >>>@@ -97,6 +111,10 @@ void __copy_page_owner(struct page *oldpage, struct page *newpage)
> >>> {
> >>> 	struct page_ext *old_ext = lookup_page_ext(oldpage);
> >>> 	struct page_ext *new_ext = lookup_page_ext(newpage);
> >>>+
> >>>+	if (unlikely(!old_ext || !new_ext))
> >>>+		return;
> >>>+
> >>> 	int i;
> >>>
> >>> 	new_ext->order = old_ext->order;
> >>>@@ -186,6 +204,11 @@ err:
> >>> void __dump_page_owner(struct page *page)
> >>> {
> >>> 	struct page_ext *page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext)) {
> >>>+		pr_alert("There is not page extension available.\n");
> >>>+		return;
> >>>+	}
> >>>+
> >>> 	struct stack_trace trace = {
> >>> 		.nr_entries = page_ext->nr_entries,
> >>> 		.entries = &page_ext->trace_entries[0],
> >>>@@ -251,6 +274,8 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
> >>> 		}
> >>>
> >>> 		page_ext = lookup_page_ext(page);
> >>>+		if (unlikely(!page_ext))
> >>>+			continue;
> >>>
> >>> 		/*
> >>> 		 * Some pages could be missed by concurrent allocation or free,
> >>>@@ -317,6 +342,8 @@ static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone)
> >>> 				continue;
> >>>
> >>> 			page_ext = lookup_page_ext(page);
> >>>+			if (unlikely(!page_ext))
> >>>+				continue;
> >>>
> >>> 			/* Maybe overraping zone */
> >>> 			if (test_bit(PAGE_EXT_OWNER, &page_ext->flags))
> >>>diff --git a/mm/page_poison.c b/mm/page_poison.c
> >>>index 1eae5fa..2e647c6 100644
> >>>--- a/mm/page_poison.c
> >>>+++ b/mm/page_poison.c
> >>>@@ -54,6 +54,9 @@ static inline void set_page_poison(struct page *page)
> >>> 	struct page_ext *page_ext;
> >>>
> >>> 	page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext))
> >>>+		return;
> >>>+
> >>> 	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> >>> }
> >>>
> >>>@@ -62,6 +65,9 @@ static inline void clear_page_poison(struct page *page)
> >>> 	struct page_ext *page_ext;
> >>>
> >>> 	page_ext = lookup_page_ext(page);
> >>>+	if (unlikely(!page_ext))
> >>>+		return;
> >>>+
> >>> 	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> >>> }
> >>>
> >>>@@ -70,7 +76,7 @@ bool page_is_poisoned(struct page *page)
> >>> 	struct page_ext *page_ext;
> >>>
> >>> 	page_ext = lookup_page_ext(page);
> >>>-	if (!page_ext)
> >>>+	if (unlikely(!page_ext))
> >>> 		return false;
> >>>
> >>> 	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> >>>diff --git a/mm/vmstat.c b/mm/vmstat.c
> >>>index 77e42ef..cb2a67b 100644
> >>>--- a/mm/vmstat.c
> >>>+++ b/mm/vmstat.c
> >>>@@ -1061,6 +1061,8 @@ static void pagetypeinfo_showmixedcount_print(struct seq_file *m,
> >>> 				continue;
> >>>
> >>> 			page_ext = lookup_page_ext(page);
> >>>+			if (unlikely(!page_ext))
> >>>+				continue;
> >>>
> >>> 			if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags))
> >>> 				continue;
> >>>--
> >>>2.0.2
> >>>
> >>>--
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> >>
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