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From: Minchan Kim <minchan@kernel.org>
To: Yang Shi <yang.shi@linaro.org>
Cc: akpm@linux-foundation.org, iamjoonsoo.kim@lge.com,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linaro-kernel@lists.linaro.org
Subject: Re: [PATCH] mm: check the return value of lookup_page_ext for all call sites
Date: Thu, 26 May 2016 09:37:19 +0900
Message-ID: <20160526003719.GB9661@bbox> (raw)
In-Reply-To: <20160524025811.GA29094@bbox>

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?

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.

> 
> 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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  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-23 17:16 Yang Shi
2016-05-24  2:58 ` Minchan Kim
2016-05-26  0:37   ` Minchan Kim [this message]
2016-05-26 23:15     ` Shi, Yang
2016-05-27  5:14       ` Minchan Kim
2016-05-27  6:08         ` Joonsoo Kim
2016-05-27  8:11           ` Minchan Kim
2016-05-27 18:16             ` Shi, Yang
2016-05-30  6:11               ` Minchan Kim
2016-06-01 20:40                 ` Shi, Yang
2016-06-02  5:00                   ` Minchan Kim
2016-06-02 23:15                     ` Shi, Yang
2016-05-30  5:39             ` Joonsoo Kim
2016-05-30  6:08               ` Minchan Kim
2016-06-01 20:52                 ` Shi, Yang
2016-05-27 20:02       ` Andrew Morton
2016-05-27 20:17         ` Shi, Yang
2016-05-27 20:30           ` Andrew Morton
2016-05-24 10:08 ` [PATCH] mm: fix build problems from lookup_page_ext Arnd Bergmann
2016-05-24 16:33   ` Shi, Yang
2016-05-25  7:12 ` [PATCH] mm: check the return value of lookup_page_ext for all call sites shakil
2016-05-30  6:17 ` Minchan Kim

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