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    Subject[PATCH 2/3] hugetlbfs: close race between MADV_DONTNEED and page fault
    Date
    From: Rik van Riel <riel@surriel.com>

    Malloc libraries, like jemalloc and tcalloc, take decisions on when
    to call madvise independently from the code in the main application.

    This sometimes results in the application page faulting on an address,
    right after the malloc library has shot down the backing memory with
    MADV_DONTNEED.

    Usually this is harmless, because we always have some 4kB pages
    sitting around to satisfy a page fault. However, with hugetlbfs
    systems often allocate only the exact number of huge pages that
    the application wants.

    Due to TLB batching, hugetlbfs MADV_DONTNEED will free pages outside of
    any lock taken on the page fault path, which can open up the following
    race condition:

    CPU 1 CPU 2

    MADV_DONTNEED
    unmap page
    shoot down TLB entry
    page fault
    fail to allocate a huge page
    killed with SIGBUS
    free page

    Fix that race by pulling the locking from __unmap_hugepage_final_range
    into helper functions called from zap_page_range_single. This ensures
    page faults stay locked out of the MADV_DONTNEED VMA until the
    huge pages have actually been freed.

    Signed-off-by: Rik van Riel <riel@surriel.com>
    ---
    include/linux/hugetlb.h | 35 +++++++++++++++++++++++++++++++++--
    mm/hugetlb.c | 20 +++++++++++---------
    mm/memory.c | 7 +++----
    3 files changed, 47 insertions(+), 15 deletions(-)

    diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
    index 694928fa06a3..d9ec500cfef9 100644
    --- a/include/linux/hugetlb.h
    +++ b/include/linux/hugetlb.h
    @@ -139,7 +139,7 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
    void unmap_hugepage_range(struct vm_area_struct *,
    unsigned long, unsigned long, struct page *,
    zap_flags_t);
    -void __unmap_hugepage_range_final(struct mmu_gather *tlb,
    +void __unmap_hugepage_range(struct mmu_gather *tlb,
    struct vm_area_struct *vma,
    unsigned long start, unsigned long end,
    struct page *ref_page, zap_flags_t zap_flags);
    @@ -246,6 +246,25 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma,
    void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
    unsigned long *start, unsigned long *end);

    +extern void __hugetlb_zap_begin(struct vm_area_struct *vma,
    + unsigned long *begin, unsigned long *end);
    +extern void __hugetlb_zap_end(struct vm_area_struct *vma,
    + struct zap_details *details);
    +
    +static inline void hugetlb_zap_begin(struct vm_area_struct *vma,
    + unsigned long *start, unsigned long *end)
    +{
    + if (is_vm_hugetlb_page(vma))
    + __hugetlb_zap_begin(vma, start, end);
    +}
    +
    +static inline void hugetlb_zap_end(struct vm_area_struct *vma,
    + struct zap_details *details)
    +{
    + if (is_vm_hugetlb_page(vma))
    + __hugetlb_zap_end(vma, details);
    +}
    +
    void hugetlb_vma_lock_read(struct vm_area_struct *vma);
    void hugetlb_vma_unlock_read(struct vm_area_struct *vma);
    void hugetlb_vma_lock_write(struct vm_area_struct *vma);
    @@ -297,6 +316,18 @@ static inline void adjust_range_if_pmd_sharing_possible(
    {
    }

    +static inline void hugetlb_zap_begin(
    + struct vm_area_struct *vma,
    + unsigned long *start, unsigned long *end)
    +{
    +}
    +
    +static inline void hugetlb_zap_end(
    + struct vm_area_struct *vma,
    + struct zap_details *details)
    +{
    +}
    +
    static inline struct page *hugetlb_follow_page_mask(
    struct vm_area_struct *vma, unsigned long address, unsigned int flags,
    unsigned int *page_mask)
    @@ -442,7 +473,7 @@ static inline long hugetlb_change_protection(
    return 0;
    }

    -static inline void __unmap_hugepage_range_final(struct mmu_gather *tlb,
    +static inline void __unmap_hugepage_range(struct mmu_gather *tlb,
    struct vm_area_struct *vma, unsigned long start,
    unsigned long end, struct page *ref_page,
    zap_flags_t zap_flags)
    diff --git a/mm/hugetlb.c b/mm/hugetlb.c
    index e859fba5bc7d..5f8b82e902a8 100644
    --- a/mm/hugetlb.c
    +++ b/mm/hugetlb.c
    @@ -5306,9 +5306,9 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma,
    return len + old_addr - old_end;
    }

    -static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
    - unsigned long start, unsigned long end,
    - struct page *ref_page, zap_flags_t zap_flags)
    +void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
    + unsigned long start, unsigned long end,
    + struct page *ref_page, zap_flags_t zap_flags)
    {
    struct mm_struct *mm = vma->vm_mm;
    unsigned long address;
    @@ -5435,16 +5435,18 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
    tlb_flush_mmu_tlbonly(tlb);
    }

    -void __unmap_hugepage_range_final(struct mmu_gather *tlb,
    - struct vm_area_struct *vma, unsigned long start,
    - unsigned long end, struct page *ref_page,
    - zap_flags_t zap_flags)
    +void __hugetlb_zap_begin(struct vm_area_struct *vma,
    + unsigned long *start, unsigned long *end)
    {
    + adjust_range_if_pmd_sharing_possible(vma, start, end);
    hugetlb_vma_lock_write(vma);
    i_mmap_lock_write(vma->vm_file->f_mapping);
    +}

    - /* mmu notification performed in caller */
    - __unmap_hugepage_range(tlb, vma, start, end, ref_page, zap_flags);
    +void __hugetlb_zap_end(struct vm_area_struct *vma,
    + struct zap_details *details)
    +{
    + zap_flags_t zap_flags = details ? details->zap_flags : 0;

    if (zap_flags & ZAP_FLAG_UNMAP) { /* final unmap */
    /*
    diff --git a/mm/memory.c b/mm/memory.c
    index 6c264d2f969c..a07ae3b60530 100644
    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -1683,7 +1683,7 @@ static void unmap_single_vma(struct mmu_gather *tlb,
    if (vma->vm_file) {
    zap_flags_t zap_flags = details ?
    details->zap_flags : 0;
    - __unmap_hugepage_range_final(tlb, vma, start, end,
    + __unmap_hugepage_range(tlb, vma, start, end,
    NULL, zap_flags);
    }
    } else
    @@ -1753,9 +1753,7 @@ void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
    lru_add_drain();
    mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
    address, end);
    - if (is_vm_hugetlb_page(vma))
    - adjust_range_if_pmd_sharing_possible(vma, &range.start,
    - &range.end);
    + hugetlb_zap_begin(vma, &range.start, &range.end);
    tlb_gather_mmu(&tlb, vma->vm_mm);
    update_hiwater_rss(vma->vm_mm);
    mmu_notifier_invalidate_range_start(&range);
    @@ -1766,6 +1764,7 @@ void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
    unmap_single_vma(&tlb, vma, address, end, details, false);
    mmu_notifier_invalidate_range_end(&range);
    tlb_finish_mmu(&tlb);
    + hugetlb_zap_end(vma, details);
    }

    /**
    --
    2.41.0
    \
     
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      Last update: 2023-09-25 22:32    [W:5.686 / U:0.012 seconds]
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