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    Subject[PATCH AUTOSEL for 4.4 003/101] userfaultfd: shmem: __do_fault requires VM_FAULT_NOPAGE
    Date
    From: Andrea Arcangeli <aarcange@redhat.com>

    [ Upstream commit 6bbc4a4144b1a69743022ac68dfaf6e7d993abb9 ]

    __do_fault assumes vmf->page has been initialized and is valid if
    VM_FAULT_NOPAGE is not returned by vma->vm_ops->fault(vma, vmf).

    handle_userfault() in turn should return VM_FAULT_NOPAGE if it doesn't
    return VM_FAULT_SIGBUS or VM_FAULT_RETRY (the other two possibilities).

    This VM_FAULT_NOPAGE case is only invoked when signal are pending and it
    didn't matter for anonymous memory before. It only started to matter
    since shmem was introduced. hugetlbfs also takes a different path and
    doesn't exercise __do_fault.

    Link: http://lkml.kernel.org/r/20170228154201.GH5816@redhat.com
    Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
    Reported-by: Dmitry Vyukov <dvyukov@google.com>
    Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
    ---
    fs/userfaultfd.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
    index 66cdb44616d5..59d58bdad7d3 100644
    --- a/fs/userfaultfd.c
    +++ b/fs/userfaultfd.c
    @@ -386,7 +386,7 @@ int handle_userfault(struct vm_area_struct *vma, unsigned long address,
    * in such case.
    */
    down_read(&mm->mmap_sem);
    - ret = 0;
    + ret = VM_FAULT_NOPAGE;
    }
    }

    --
    2.11.0
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