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    Subject[PATCH v2 20/33] mm/mmap: write-lock adjacent VMAs if they can grow into unmapped area
    From
    While unmapping VMAs, adjacent VMAs might be able to grow into the area
    being unmapped. In such cases write-lock adjacent VMAs to prevent this
    growth.

    Signed-off-by: Suren Baghdasaryan <surenb@google.com>
    ---
    mm/mmap.c | 8 +++++---
    1 file changed, 5 insertions(+), 3 deletions(-)

    diff --git a/mm/mmap.c b/mm/mmap.c
    index 57cb3a2ac9b1..3baf218836bb 100644
    --- a/mm/mmap.c
    +++ b/mm/mmap.c
    @@ -2399,11 +2399,13 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
    * down_read(mmap_lock) and collide with the VMA we are about to unmap.
    */
    if (downgrade) {
    - if (next && (next->vm_flags & VM_GROWSDOWN))
    + if (next && (next->vm_flags & VM_GROWSDOWN)) {
    + vma_start_write(next);
    downgrade = false;
    - else if (prev && (prev->vm_flags & VM_GROWSUP))
    + } else if (prev && (prev->vm_flags & VM_GROWSUP)) {
    + vma_start_write(prev);
    downgrade = false;
    - else
    + } else
    mmap_write_downgrade(mm);
    }

    --
    2.39.1
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