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    Subject[PATCH 3.18 069/134] mm, memory_hotplug: is_mem_section_removable do not pass the end of a zone
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

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

    [ Upstream commit efad4e475c312456edb3c789d0996d12ed744c13 ]

    Patch series "mm, memory_hotplug: fix uninitialized pages fallouts", v2.

    Mikhail Zaslonko has posted fixes for the two bugs quite some time ago
    [1]. I have pushed back on those fixes because I believed that it is
    much better to plug the problem at the initialization time rather than
    play whack-a-mole all over the hotplug code and find all the places
    which expect the full memory section to be initialized.

    We have ended up with commit 2830bf6f05fb ("mm, memory_hotplug:
    initialize struct pages for the full memory section") merged and cause a
    regression [2][3]. The reason is that there might be memory layouts
    when two NUMA nodes share the same memory section so the merged fix is
    simply incorrect.

    In order to plug this hole we really have to be zone range aware in
    those handlers. I have split up the original patch into two. One is
    unchanged (patch 2) and I took a different approach for `removable'
    crash.

    [1] http://lkml.kernel.org/r/20181105150401.97287-2-zaslonko@linux.ibm.com
    [2] https://bugzilla.redhat.com/show_bug.cgi?id=1666948
    [3] http://lkml.kernel.org/r/20190125163938.GA20411@dhcp22.suse.cz

    This patch (of 2):

    Mikhail has reported the following VM_BUG_ON triggered when reading sysfs
    removable state of a memory block:

    page:000003d08300c000 is uninitialized and poisoned
    page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
    Call Trace:
    is_mem_section_removable+0xb4/0x190
    show_mem_removable+0x9a/0xd8
    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:
    is_mem_section_removable+0xb4/0x190
    Kernel panic - not syncing: Fatal exception: panic_on_oops

    The reason is that the memory block spans the zone boundary and we are
    stumbling over an unitialized struct page. Fix this by enforcing zone
    range in is_mem_section_removable so that we never run away from a zone.

    Link: http://lkml.kernel.org/r/20190128144506.15603-2-mhocko@kernel.org
    Signed-off-by: Michal Hocko <mhocko@suse.com>
    Reported-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
    Debugged-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
    Tested-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
    Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
    Reviewed-by: Oscar Salvador <osalvador@suse.de>
    Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
    Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
    Cc: Martin Schwidefsky <schwidefsky@de.ibm.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, 2 insertions(+), 1 deletion(-)

    diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
    index 05014e89efae..3fb2067c36a4 100644
    --- a/mm/memory_hotplug.c
    +++ b/mm/memory_hotplug.c
    @@ -1321,7 +1321,8 @@ static struct page *next_active_pageblock(struct page *page)
    int is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages)
    {
    struct page *page = pfn_to_page(start_pfn);
    - struct page *end_page = page + nr_pages;
    + unsigned long end_pfn = min(start_pfn + nr_pages, zone_end_pfn(page_zone(page)));
    + struct page *end_page = pfn_to_page(end_pfn);

    /* Check the starting page of each pageblock within the range */
    for (; page < end_page; page = next_active_pageblock(page)) {
    --
    2.19.1


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