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@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? > > 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 > >>> > >>>-- > >>>To unsubscribe, send a message with 'unsubscribe linux-mm' in > >>>the body to majordomo@xxxxxxxxx. For more info on Linux MM, > >>>see: http://www.linux-mm.org/ . > >>>Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > >> > >>-- > >>To unsubscribe, send a message with 'unsubscribe linux-mm' in > >>the body to majordomo@xxxxxxxxx. For more info on Linux MM, > >>see: http://www.linux-mm.org/ . > >>Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>