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    Subject[PATCH 4.9 61/96] mm, memory_hotplug: test_pages_in_a_zone do not pass the end of zone
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    [ Upstream commit 24feb47c5fa5b825efb0151f28906dfdad027e61 ]

    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 pages access from
    test_pages_in_a_zone() function triggered by memory_hotplug sysfs
    handlers.

    Here are the the panic examples:
    CONFIG_DEBUG_VM_PGFLAGS=y
    kernel parameter mem=2050M
    --------------------------
    page:000003d082008000 is uninitialized and poisoned
    page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
    Call Trace:
    test_pages_in_a_zone+0xde/0x160
    show_valid_zones+0x5c/0x190
    dev_attr_show+0x34/0x70
    sysfs_kf_seq_show+0xc8/0x148
    seq_read+0x204/0x480
    __vfs_read+0x32/0x178
    vfs_read+0x82/0x138
    ksys_read+0x5a/0xb0
    system_call+0xdc/0x2d8
    Last Breaking-Event-Address:
    test_pages_in_a_zone+0xde/0x160
    Kernel panic - not syncing: Fatal exception: panic_on_oops

    Fix this by checking whether the pfn to check is within the zone.

    [mhocko@suse.com: separated this change from http://lkml.kernel.org/r/20181105150401.97287-2-zaslonko@linux.ibm.com]
    Link: http://lkml.kernel.org/r/20190128144506.15603-3-mhocko@kernel.org

    [mhocko@suse.com: separated this change from
    http://lkml.kernel.org/r/20181105150401.97287-2-zaslonko@linux.ibm.com]
    Signed-off-by: Michal Hocko <mhocko@suse.com>
    Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
    Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
    Reviewed-by: Oscar Salvador <osalvador@suse.de>
    Tested-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
    Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
    Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
    Cc: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
    Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    mm/memory_hotplug.c | 3 +++
    1 file changed, 3 insertions(+)

    diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
    index a03a401f11b6..b4c8d7b9ab82 100644
    --- a/mm/memory_hotplug.c
    +++ b/mm/memory_hotplug.c
    @@ -1512,6 +1512,9 @@ int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn,
    i++;
    if (i == MAX_ORDER_NR_PAGES || pfn + i >= end_pfn)
    continue;
    + /* Check if we got outside of the zone */
    + if (zone && !zone_spans_pfn(zone, pfn + i))
    + return 0;
    page = pfn_to_page(pfn + i);
    if (zone && page_zone(page) != zone)
    return 0;
    --
    2.19.1


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