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    Subject[PATCH v2 18/33] mm: write-lock VMAs before removing them from VMA tree
    From
    Write-locking VMAs before isolating them ensures that page fault
    handlers don't operate on isolated VMAs.

    Signed-off-by: Suren Baghdasaryan <surenb@google.com>
    ---
    mm/mmap.c | 1 +
    mm/nommu.c | 5 +++++
    2 files changed, 6 insertions(+)

    diff --git a/mm/mmap.c b/mm/mmap.c
    index b3c247073aa0..5bdfd087b632 100644
    --- a/mm/mmap.c
    +++ b/mm/mmap.c
    @@ -2261,6 +2261,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
    static inline int munmap_sidetree(struct vm_area_struct *vma,
    struct ma_state *mas_detach)
    {
    + vma_start_write(vma);
    mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1);
    if (mas_store_gfp(mas_detach, vma, GFP_KERNEL))
    return -ENOMEM;
    diff --git a/mm/nommu.c b/mm/nommu.c
    index 57ba243c6a37..2ab162d773e2 100644
    --- a/mm/nommu.c
    +++ b/mm/nommu.c
    @@ -588,6 +588,7 @@ static int delete_vma_from_mm(struct vm_area_struct *vma)
    current->pid);
    return -ENOMEM;
    }
    + vma_start_write(vma);
    cleanup_vma_from_mm(vma);

    /* remove from the MM's tree and list */
    @@ -1519,6 +1520,10 @@ void exit_mmap(struct mm_struct *mm)
    */
    mmap_write_lock(mm);
    for_each_vma(vmi, vma) {
    + /*
    + * No need to lock VMA because this is the only mm user and no
    + * page fault handled can race with it.
    + */
    cleanup_vma_from_mm(vma);
    delete_vma(mm, vma);
    cond_resched();
    --
    2.39.1
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