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)]; +} + + 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 (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; - - 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; + 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 */ -- Thanks, David / dhildenb
