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    SubjectRE: Hugepage regression
    Date
    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.


    Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>

    --- ./fs/hugetlbfs/inode.c.orig 2006-10-05 10:25:20.000000000 -0700
    +++ ./fs/hugetlbfs/inode.c 2006-10-10 14:27:48.000000000 -0700
    @@ -293,7 +293,7 @@ hugetlb_vmtruncate_list(struct prio_tree
    if (h_vm_pgoff >= h_pgoff)
    v_offset = 0;

    - unmap_hugepage_range(vma,
    + __unmap_hugepage_range(vma,
    vma->vm_start + v_offset, vma->vm_end);
    }
    }
    --- ./mm/hugetlb.c.orig 2006-10-05 10:25:21.000000000 -0700
    +++ ./mm/hugetlb.c 2006-10-10 14:27:48.000000000 -0700
    @@ -356,8 +356,8 @@ nomem:
    return -ENOMEM;
    }

    -void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
    - unsigned long end)
    +void __unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
    + unsigned long end)
    {
    struct mm_struct *mm = vma->vm_mm;
    unsigned long address;
    @@ -398,6 +398,24 @@ void unmap_hugepage_range(struct vm_area
    }
    }

    +void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
    + unsigned long end)
    +{
    + /*
    + * It is undesirable to test vma->vm_file as it should be non-null
    + * for valid hugetlb area. However, vm_file will be NULL in the error
    + * cleanup path of do_mmap_pgoff. When hugetlbfs ->mmap method fails,
    + * do_mmap_pgoff() nullifies vma->vm_file before calling this function
    + * to clean up. Since no pte has actually been setup, it is safe to
    + * do nothing in this case.
    + */
    + if (vma->vm_file) {
    + spin_lock(&vma->vm_file->f_mapping->i_mmap_lock);
    + __unmap_hugepage_range(vma, start, end);
    + spin_unlock(&vma->vm_file->f_mapping->i_mmap_lock);
    + }
    +}
    +
    static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
    unsigned long address, pte_t *ptep, pte_t pte)
    {
    --- ./include/linux/hugetlb.h.orig 2006-10-05 10:25:21.000000000 -0700
    +++ ./include/linux/hugetlb.h 2006-10-10 13:08:48.000000000 -0700
    @@ -17,6 +17,7 @@ int hugetlb_sysctl_handler(struct ctl_ta
    int copy_hugetlb_page_range(struct mm_struct *, struct mm_struct *, struct vm_area_struct *);
    int follow_hugetlb_page(struct mm_struct *, struct vm_area_struct *, struct page **, struct vm_area_struct **, unsigned long *, int
    *, int);
    void unmap_hugepage_range(struct vm_area_struct *, unsigned long, unsigned long);
    +void __unmap_hugepage_range(struct vm_area_struct *, unsigned long, unsigned long);
    int hugetlb_prefault(struct address_space *, struct vm_area_struct *);
    int hugetlb_report_meminfo(char *);
    int hugetlb_report_node_meminfo(int, char *);


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