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

From: Minchan Kim
Date: Wed May 25 2016 - 20:37:10 EST

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@xxxxxxxxxx>
>
> 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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