Do I need spin_lock before pgd/pmd/pte_offset?

[Timur Tabi <timur.tabi@ammasso.com>]

I can't seem to find a definitive answer to this question.  I have this 
code which takes a user-space virtual address and converts it to a 
physical address:

        pgd_t *pgd = pgd_offset(current->mm, address);
        pmd_t *pmd = pmd_offset(pgd, address);
        pte_t *pte = pte_offset_map(pmd, address);
        pte_t _pte = *pte;
        pte_unmap(pte);

        return pte_val(_pte) & PTE_MASK;

Nothing unusual here.  The question is, do I need to protect this code 
with a spinlock?  That is, should I change the above to:

	spin_lock(&current->mm->page_table_lock);
        pgd_t *pgd = pgd_offset(current->mm, address);
        pmd_t *pmd = pmd_offset(pgd, address);
        pte_t *pte = pte_offset_map(pmd, address);
        pte_t _pte = *pte;
        pte_unmap(pte);
	spin_unlock(&current->mm->page_table_lock);

I'm guessing I only need to call a spinlock if the page isn't locked in 
memory.  Is that correct?

--
Timur Tabi
Staff Software Engineer
timur.tabi@ammasso.com

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