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    Subject[v6 02/15] x86/mm: setting fields in deferred pages
    Date
    Without deferred struct page feature (CONFIG_DEFERRED_STRUCT_PAGE_INIT),
    flags and other fields in "struct page"es are never changed prior to first
    initializing struct pages by going through __init_single_page().

    With deferred struct page feature enabled there is a case where we set some
    fields prior to initializing:

    mem_init() {
    register_page_bootmem_info();
    free_all_bootmem();
    ...
    }

    When register_page_bootmem_info() is called only non-deferred struct pages
    are initialized. But, this function goes through some reserved pages which
    might be part of the deferred, and thus are not yet initialized.

    mem_init
    register_page_bootmem_info
    register_page_bootmem_info_node
    get_page_bootmem
    .. setting fields here ..
    such as: page->freelist = (void *)type;

    We end-up with similar issue as in the previous patch, where currently we
    do not observe problem as memory is zeroed. But, if flag asserts are
    changed we can start hitting issues.

    Also, because in this patch series we will stop zeroing struct page memory
    during allocation, we must make sure that struct pages are properly
    initialized prior to using them.

    The deferred-reserved pages are initialized in free_all_bootmem().
    Therefore, the fix is to switch the above calls.

    Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
    Reviewed-by: Steven Sistare <steven.sistare@oracle.com>
    Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
    Reviewed-by: Bob Picco <bob.picco@oracle.com>
    ---
    arch/x86/mm/init_64.c | 9 +++++++--
    1 file changed, 7 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
    index 136422d7d539..1e863baec847 100644
    --- a/arch/x86/mm/init_64.c
    +++ b/arch/x86/mm/init_64.c
    @@ -1165,12 +1165,17 @@ void __init mem_init(void)

    /* clear_bss() already clear the empty_zero_page */

    - register_page_bootmem_info();
    -
    /* this will put all memory onto the freelists */
    free_all_bootmem();
    after_bootmem = 1;

    + /* Must be done after boot memory is put on freelist, because here we
    + * might set fields in deferred struct pages that have not yet been
    + * initialized, and free_all_bootmem() initializes all the reserved
    + * deferred pages for us.
    + */
    + register_page_bootmem_info();
    +
    /* Register memory areas for /proc/kcore */
    kclist_add(&kcore_vsyscall, (void *)VSYSCALL_ADDR,
    PAGE_SIZE, KCORE_OTHER);
    --
    2.14.0
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