Hello, On 10.12.2018 14:24, Michal Hocko wrote: > 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). Yes, I should probably keep full failure samples from my previous patch version. > >> 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? Well, as you were also suggesting earlier: 'If we do not have a zone which spans the rest of the section'. I'm not sure how else we should verify that. Moreover, I was able to recreate the problem only with the highest zone (memory end is not on the 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 > Thanks, Mikhail Zaslonko
