Re: [PATCH 4/5] teach smaps_pte_range() about THP pmds

Dave Hansen
2011-02-10T19:32:55Z

On Thu, 2011-02-10 at 19:08 +0100, Andrea Arcangeli wrote:
> the locking looks wrong, who is taking the &walk->mm->page_table_lock,
> and isn't this going to deadlock on the pte_offset_map_lock for
> NR_CPUS < 4, and where is it released? This spin_lock don't seem
> necessary to me.
>
> The right locking would be:
>
> spin_lock(&walk->mm->page_table_lock);
> if (pmd_trans_huge(*pmd)) {
> if (pmd_trans_splitting(*pmd)) {
> spin_unlock(&walk->mm->page_table_lock);
> wait_split_huge_page(vma->anon_vma, pmd);
> } else {
> smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_SIZE, walk);
> spin_unlock(&walk->mm->page_table_lock);
> return 0;
> }

I was under the assumption that the mm->page_table_lock was already held
here, but I think that's wrong. I'll go back, take another look, and
retest.

-- Dave