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    Subject[02/34] mm: fix ia64 crash when gcore reads gate area
    2.6.32-stable review patch.  If anyone has any objections, please let us know.

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

    From: Hugh Dickins <hughd@google.com>

    commit de51257aa301652876ab6e8f13ea4eadbe4a3846 upstream.

    Debian's ia64 autobuilders have been seeing kernel freeze or reboot
    when running the gdb testsuite (Debian bug 588574): dannf bisected to
    2.6.32 62eede62dafb4a6633eae7ffbeb34c60dba5e7b1 "mm: ZERO_PAGE without
    PTE_SPECIAL"; and reproduced it with gdb's gcore on a simple target.

    I'd missed updating the gate_vma handling in __get_user_pages(): that
    happens to use vm_normal_page() (nowadays failing on the zero page),
    yet reported success even when it failed to get a page - boom when
    access_process_vm() tried to copy that to its intermediate buffer.

    Fix this, resisting cleanups: in particular, leave it for now reporting
    success when not asked to get any pages - very probably safe to change,
    but let's not risk it without testing exposure.

    Why did ia64 crash with 16kB pages, but succeed with 64kB pages?
    Because setup_gate() pads each 64kB of its gate area with zero pages.

    Reported-by: Andreas Barth <aba@not.so.argh.org>
    Bisected-by: dann frazier <dannf@debian.org>
    Signed-off-by: Hugh Dickins <hughd@google.com>
    Tested-by: dann frazier <dannf@dannf.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    mm/memory.c | 16 +++++++++++++---
    1 file changed, 13 insertions(+), 3 deletions(-)

    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -1282,10 +1282,20 @@ int __get_user_pages(struct task_struct
    return i ? : -EFAULT;
    }
    if (pages) {
    - struct page *page = vm_normal_page(gate_vma, start, *pte);
    + struct page *page;
    +
    + page = vm_normal_page(gate_vma, start, *pte);
    + if (!page) {
    + if (!(gup_flags & FOLL_DUMP) &&
    + is_zero_pfn(pte_pfn(*pte)))
    + page = pte_page(*pte);
    + else {
    + pte_unmap(pte);
    + return i ? : -EFAULT;
    + }
    + }
    pages[i] = page;
    - if (page)
    - get_page(page);
    + get_page(page);
    }
    pte_unmap(pte);
    if (vmas)



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