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    SubjectRe: [PATCH 1/1] mm, memory_hotplug: Initialize struct pages for the full memory section
    On Mon, Dec 10, 2018 at 02:07:12PM +0100, 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. 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.
    >
    >Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
    >Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
    >Cc: <stable@vger.kernel.org>
    >---
    > 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

    If my understanding is correct, end_pfn is not a valid range.

    memmap_init_zone() initialize the range [start_pfn, start_pfn + size). I
    am afraid this will break the syntax.

    And max_pfn is also not a valid one. For example, on x86,
    update_end_of_memory_vars() will update max_pfn, which is calculated by:

    end_pfn = PFN_UP(start + size);

    BTW, as you mentioned this apply to hotplug case. And then why this couldn't
    happen during boot up? What differ these two cases?

    > }
    >
    > #ifdef CONFIG_ZONE_DEVICE
    >--
    >2.16.4

    --
    Wei Yang
    Help you, Help me

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