On Mon 10-12-18 14:07:12, Mikhail Zaslonko wrote: > If memory end is not aligned with the sparse memory section boundary, the > mapping of such a section is only partly initialized. It would be great to mention how you can end up in the situation like this(a user provided memmap or a strange HW). > This may lead to > VM_BUG_ON due to uninitialized struct page access from > is_mem_section_removable() or test_pages_in_a_zone() function triggered by > memory_hotplug sysfs handlers: > > page:000003d082008000 is uninitialized and poisoned > page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) > Call Trace: > ([<0000000000385b26>] test_pages_in_a_zone+0xde/0x160) > [<00000000008f15c4>] show_valid_zones+0x5c/0x190 > [<00000000008cf9c4>] dev_attr_show+0x34/0x70 > [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148 > [<00000000003e4194>] seq_read+0x204/0x480 > [<00000000003b53ea>] __vfs_read+0x32/0x178 > [<00000000003b55b2>] vfs_read+0x82/0x138 > [<00000000003b5be2>] ksys_read+0x5a/0xb0 > [<0000000000b86ba0>] system_call+0xdc/0x2d8 > Last Breaking-Event-Address: > [<0000000000385b26>] test_pages_in_a_zone+0xde/0x160 > Kernel panic - not syncing: Fatal exception: panic_on_oops > > Fix the problem by initializing the last memory section of the highest zone > in memmap_init_zone() till the very end, even if it goes beyond the zone > end. Why do we need to restrict this to the highest zone? In other words, why cannot we do what I was suggesting earlier [1]. What does prevent other zones to have an incomplete section boundary? [1] http://lkml.kernel.org/r/20181105183533.GQ4361@xxxxxxxxxxxxxx > Signed-off-by: Mikhail Zaslonko <zaslonko@xxxxxxxxxxxxx> > Reviewed-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > --- > mm/page_alloc.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 2ec9cc407216..41ef5508e5f1 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5542,6 +5542,21 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone, > cond_resched(); > } > } > +#ifdef CONFIG_SPARSEMEM > + /* > + * If there is no zone spanning the rest of the section > + * then we should at least initialize those pages. Otherwise we > + * could blow up on a poisoned page in some paths which depend > + * on full sections being initialized (e.g. memory hotplug). > + */ > + if (end_pfn == max_pfn) { > + while (end_pfn % PAGES_PER_SECTION) { > + __init_single_page(pfn_to_page(end_pfn), end_pfn, zone, > + nid); > + end_pfn++; > + } > + } > +#endif > } > > #ifdef CONFIG_ZONE_DEVICE > -- > 2.16.4 -- Michal Hocko SUSE Labs
