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    SubjectRe: Hugepage regression
    On Tue, Oct 10, 2006 at 04:34:40PM -0700, Chen, Kenneth W wrote:
    > Hugh Dickins wrote on Tuesday, October 10, 2006 12:18 PM
    > > Yes, I'd expect your i_mmap_lock to solve the problem: and since
    > > you're headed in that direction anyway, it makes most sense to use
    > > that solution rather than get into defining arrays, or sacrificing
    > > the lazy flush, or risking page_count races.
    > >
    > > So please extract the __unmap_hugepage_range mods from your shared
    > > pagetable patch, and use that to fix the bug.
    >
    >
    > OK, here is a bug fix patch fixing earlier "bug fix" patch :-(
    >
    >
    > [patch] hugetlb: fix linked list corruption in unmap_hugepage_range
    >
    > commit fe1668ae5bf0145014c71797febd9ad5670d5d05 causes kernel to oops with
    > libhugetlbfs test suite. The problem is that hugetlb pages can be shared
    > by multiple mappings. Multiple threads can fight over page->lru in the unmap
    > path and bad things happen. We now serialize __unmap_hugepage_range to void
    > concurrent linked list manipulation. Such serialization is also needed for
    > shared page table page on hugetlb area. This patch will fixed the bug and
    > also serve as a prepatch for shared page table.

    Can I suggest that you put a big comment on the linked list
    declaration itself saying that you're relying on serialization here.
    Otherwise I'm worried someone will try to de-serialize it again, and
    break it without realizing. Given the number of people who failed to
    spot the problem with the patch the first time around..

    --
    David Gibson | I'll have my music baroque, and my code
    david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
    | _way_ _around_!
    http://www.ozlabs.org/~dgibson
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