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

On 5/27/2016 1:02 PM, Andrew Morton wrote:

On Thu, 26 May 2016 16:15:28 -0700 "Shi, Yang" yang.shi@linaro.org wrote:

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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.

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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've lost the plot here. What is the status of this patch?

Latest version:

Yes, this is the latest version. We are discussing about some future optimization.

And, Minchan Kim pointed out a possible race condition which exists even before this patch. I proposed a quick fix, as long as they are happy to the fix, I will post it to the mailing list.

Thanks, Yang

From: Yang Shi yang.shi@linaro.org Subject: mm: check the return value of lookup_page_ext for all call sites

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

[akpm@linux-foundation.org: fix build-breaking typos] [arnd@arndb.de: fix build problems from lookup_page_ext] Link: http://lkml.kernel.org/r/6285269.2CksypHdYp@wuerfel [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/1464023768-31025-1-git-send-email-yang.shi@linaro.o... Signed-off-by: Yang Shi yang.shi@linaro.org Signed-off-by: Arnd Bergmann arnd@arndb.de Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Signed-off-by: Andrew Morton akpm@linux-foundation.org

---

include/linux/page_idle.h | 43 ++++++++++++++++++++++++++++++------ mm/page_alloc.c | 6 +++++ mm/page_owner.c | 26 +++++++++++++++++++++ mm/page_poison.c | 8 +++++- mm/vmstat.c | 2 + 5 files changed, 77 insertions(+), 8 deletions(-)

diff -puN include/linux/page_idle.h~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites include/linux/page_idle.h --- a/include/linux/page_idle.h~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites +++ a/include/linux/page_idle.h @@ -46,33 +46,62 @@ extern struct page_ext_operations page_i

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 = 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 = 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 = 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 = 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 = 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 = lookup_page_ext(page);
• if (unlikely(!page_ext))

• return;
  

• clear_bit(PAGE_EXT_IDLE, &page_ext->flags);

} #endif /* CONFIG_64BIT */

diff -puN mm/page_alloc.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/page_alloc.c --- a/mm/page_alloc.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites +++ a/mm/page_alloc.c @@ -656,6 +656,9 @@ static inline void set_page_guard(struct 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(stru 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 -puN mm/page_owner.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/page_owner.c --- a/mm/page_owner.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites +++ a/mm/page_owner.c @@ -55,6 +55,8 @@ void __reset_page_owner(struct page *pag

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 +64,7 @@ void __reset_page_owner(struct page *pag void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask) { struct page_ext *page_ext = lookup_page_ext(page);

• struct stack_trace trace = { .nr_entries = 0, .max_entries = ARRAY_SIZE(page_ext->trace_entries),

@@ -69,6 +72,9 @@ void __set_page_owner(struct page *page, .skip = 3, };

• if (unlikely(!page_ext))

• return;
  

• save_stack_trace(&trace);

  page_ext->order = order;

@@ -82,6 +88,8 @@ void __set_page_owner(struct page *page, 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(str 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;

} @@ -99,6 +113,9 @@ void __copy_page_owner(struct page *oldp struct page_ext *new_ext = lookup_page_ext(newpage); int i;

• if (unlikely(!old_ext || !new_ext))

• return;
  

• new_ext->order = old_ext->order; new_ext->gfp_mask = old_ext->gfp_mask; new_ext->nr_entries = old_ext->nr_entries;

@@ -193,6 +210,11 @@ void __dump_page_owner(struct page *page gfp_t gfp_mask = page_ext->gfp_mask; int mt = gfpflags_to_migratetype(gfp_mask);

• if (unlikely(!page_ext)) {

• pr_alert("There is not page extension available.\n");
  

• return;
  

• }
• if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) { pr_alert("page_owner info is not active (free page?)\n"); return;

@@ -251,6 +273,8 @@ read_page_owner(struct file *file, char }

page_ext = lookup_page_ext(page);

• if (unlikely(!page_ext))
  

• 	continue;
  
  

  /*

  • Some pages could be missed by concurrent allocation or free,

@@ -317,6 +341,8 @@ static void init_pages_in_zone(pg_data_t 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 -puN mm/page_poison.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/page_poison.c --- a/mm/page_poison.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites +++ a/mm/page_poison.c @@ -54,6 +54,9 @@ static inline void set_page_poison(struc 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(str 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 -puN mm/vmstat.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/vmstat.c --- a/mm/vmstat.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites +++ a/mm/vmstat.c @@ -1061,6 +1061,8 @@ static void pagetypeinfo_showmixedcount_ continue;

	page_ext = lookup_page_ext(page);

• 	if (unlikely(!page_ext))
  

• 		continue;
  
  if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags))
  	continue;
  

_