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    SubjectRe: [PATCH v3 1/2] mm: protect free_pgtables with mmap_lock write lock in exit_mmap
    On Tue, Dec 07, 2021 at 03:08:19PM -0800, Suren Baghdasaryan wrote:
    > > > /**
    > > > * @close: Called when the VMA is being removed from the MM.
    > > > * Context: Caller holds mmap_lock.
    >
    > BTW, is the caller always required to hold mmap_lock for write or it
    > *might* hold it?

    __do_munmap() might hold it for read, thanks to:

    if (downgrade)
    mmap_write_downgrade(mm);

    Should probably say:

    * Context: User context. May sleep. Caller holds mmap_lock.

    I don't think we should burden the implementor of the vm_ops with the
    knowledge that the VM chooses to not hold the mmap_lock under certain
    circumstances when it doesn't matter whether it's holding the mmap_lock
    or not.

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