David Hildenbrand <david@xxxxxxxxxx> writes: > On 26.08.19 18:20, David Hildenbrand wrote: >> On 26.08.19 18:01, Aneesh Kumar K.V wrote: >>> On 8/26/19 9:13 PM, David Hildenbrand wrote: >>>> On 26.08.19 16:53, Aneesh Kumar K.V wrote: >>>>> David Hildenbrand <david@xxxxxxxxxx> writes: >>>>> >>>>>> >>> >>> .... >>> >>>>> >>>>> I did report a variant of the issue at >>>>> >>>>> https://lore.kernel.org/linux-mm/20190514025354.9108-1-aneesh.kumar@xxxxxxxxxxxxx/ >>>>> >>>>> This patch series still doesn't handle the fact that struct page backing >>>>> the start_pfn might not be initialized. ie, it results in crash like >>>>> below >>>> >>>> Okay, that's a related but different issue I think. >>>> >>>> I can see that current shrink_zone_span() might read-access the >>>> uninitialized struct page of a PFN if >>>> >>>> 1. The zone has holes and we check for "zone all holes". If we get >>>> pfn_valid(pfn), we check if "page_zone(pfn_to_page(pfn)) != zone". >>>> >>>> 2. Via find_smallest_section_pfn() / find_biggest_section_pfn() find a >>>> spanned pfn_valid(). We check >>>> - pfn_to_nid(start_pfn) != nid >>>> - zone != page_zone(pfn_to_page(start_pfn) >>>> >>>> So we don't actually use the zone/nid, only use it to sanity check. That >>>> might result in false-positives (not that bad). >>>> >>>> It all boils down to shrink_zone_span() not working only on active >>>> memory, for which the PFN is not only valid but also initialized >>>> (something for which we need a new section flag I assume). >>>> >>>> Which access triggers the issue you describe? pfn_to_nid()? >>>> >>>>> >>>>> pc: c0000000004bc1ec: shrink_zone_span+0x1bc/0x290 >>>>> lr: c0000000004bc1e8: shrink_zone_span+0x1b8/0x290 >>>>> sp: c0000000dac7f910 >>>>> msr: 800000000282b033 >>>>> current = 0xc0000000da2fa000 >>>>> paca = 0xc00000000fffb300 irqmask: 0x03 irq_happened: 0x01 >>>>> pid = 1224, comm = ndctl >>>>> kernel BUG at /home/kvaneesh/src/linux/include/linux/mm.h:1088! >>>>> Linux version 5.3.0-rc6-17495-gc7727d815970-dirty (kvaneesh@ltc-boston123) (gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04.1)) #183 SMP Mon Aug 26 09:37:32 CDT 2019 >>>>> enter ? for help >>>> >>>> Which exact kernel BUG are you hitting here? (my tree doesn't seem t >>>> have any BUG statement around include/linux/mm.h:1088). >>> >>> >>> >>> This is against upstream linus with your patches applied. >> >> I'm >> >>> >>> >>> static inline int page_to_nid(const struct page *page) >>> { >>> struct page *p = (struct page *)page; >>> >>> return (PF_POISONED_CHECK(p)->flags >> NODES_PGSHIFT) & NODES_MASK; >>> } >>> >>> >>> #define PF_POISONED_CHECK(page) ({ \ >>> VM_BUG_ON_PGFLAGS(PagePoisoned(page), page); \ >>> page; }) >>> # >>> >>> >>> It is the node id access. >> >> A right. A temporary hack would be to assume in these functions >> (shrink_zone_span() and friends) that we might have invalid NIDs / >> zonenumbers and simply skip these. After all we're only using them for >> finding zone boundaries. Not what we ultimately want, but I think until >> we have a proper SECTION_ACTIVE, it might take a while. >> > > I am talking about something as hacky as this: > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 8d1c7313ab3f..57ed3dd76a4f 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1099,6 +1099,7 @@ static inline int page_zone_id(struct page *page) > > #ifdef NODE_NOT_IN_PAGE_FLAGS > extern int page_to_nid(const struct page *page); > +#define __page_to_nid page_to_nid > #else > static inline int page_to_nid(const struct page *page) > { > @@ -1106,6 +1107,10 @@ static inline int page_to_nid(const struct page > *page) > > return (PF_POISONED_CHECK(p)->flags >> NODES_PGSHIFT) & NODES_MASK; > } > +static inline int __page_to_nid(const struct page *page) > +{ > + return ((page)->flags >> NODES_PGSHIFT) & NODES_MASK; > +} > #endif > > #ifdef CONFIG_NUMA_BALANCING > @@ -1249,6 +1254,12 @@ static inline struct zone *page_zone(const struct > page *page) > return &NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)]; > } > > +static inline struct zone *__page_zone(const struct page *page) > +{ > + return &NODE_DATA(__page_to_nid(page))->node_zones[page_zonenum(page)]; > +} We don't need that. We can always do an explicity __page_to_nid check and break from the loop before doing a page_zone() ? Also if the struct page is poisoned, we should not trust the page_zonenum()? > + > + > static inline pg_data_t *page_pgdat(const struct page *page) > { > return NODE_DATA(page_to_nid(page)); > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 49ca3364eb70..378b593d1fe1 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -334,10 +334,10 @@ static unsigned long find_smallest_section_pfn(int > nid, struct zone *zone, > if (unlikely(!pfn_valid(start_pfn))) > continue; > > - if (unlikely(pfn_to_nid(start_pfn) != nid)) > + /* We might have uninitialized memmaps */ > + if (unlikely(__page_to_nid(pfn_to_page(start_pfn)) != nid)) > continue; if we are here we got non poisoned struct page. Hence we don't need the below change? > - > - if (zone && zone != page_zone(pfn_to_page(start_pfn))) > + if (zone && zone != __page_zone(pfn_to_page(start_pfn))) > continue; > > return start_pfn; > @@ -359,10 +359,10 @@ static unsigned long find_biggest_section_pfn(int > nid, struct zone *zone, > if (unlikely(!pfn_valid(pfn))) > continue; > > - if (unlikely(pfn_to_nid(pfn) != nid)) > + /* We might have uninitialized memmaps */ > + if (unlikely(__page_to_nid(pfn_to_page(pfn)) != nid)) > continue; same as above > - > - if (zone && zone != page_zone(pfn_to_page(pfn))) > + if (zone && zone != __page_zone(pfn_to_page(pfn))) > continue; > > return pfn; > @@ -418,7 +418,10 @@ static void shrink_zone_span(struct zone *zone, > unsigned long start_pfn, > if (unlikely(!pfn_valid(pfn))) > continue; > > - if (page_zone(pfn_to_page(pfn)) != zone) > + /* We might have uninitialized memmaps */ > + if (unlikely(__page_to_nid(pfn_to_page(pfn)) != nid)) > + continue; same as above? > + if (__page_zone(pfn_to_page(pfn)) != zone) > continue; > > /* Skip range to be removed */ > @@ -483,7 +486,8 @@ static void shrink_pgdat_span(struct pglist_data *pgdat, > if (unlikely(!pfn_valid(pfn))) > continue; > > - if (pfn_to_nid(pfn) != nid) > + /* We might have uninitialized memmaps */ > + if (unlikely(__page_to_nid(pfn_to_page(pfn)) != nid)) > continue; > > /* Skip range to be removed */ > But I am not sure whether this is the right approach. -aneesh
