On Tue, 28 Oct 2014, Kirill A. Shutemov wrote:
> There's no modification to anon_vma interval tree. We only need to
> serialize against exclusive rmap walker who want s to catch all ptes the
> page is mapped with. Shared lock is enough for that.
>
> Suggested-by: Davidlohr Bueso <dbueso@xxxxxxx>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
NAK: please read Michel's comment on need_rmap_locks again, there is
no point in using read locks on anon_vma (and i_mmap) here, those will
not exclude the read locks on anon_vma (and i_mmap) in the rmap walk,
while we move ptes around.
Or am I confused?
Hugh
> ---
> mm/mremap.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index c855922497a3..1e35ba664406 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -123,7 +123,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
> }
> if (vma->anon_vma) {
> anon_vma = vma->anon_vma;
> - anon_vma_lock_write(anon_vma);
> + anon_vma_lock_read(anon_vma);
> }
> }
>
> @@ -154,7 +154,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
> pte_unmap(new_pte - 1);
> pte_unmap_unlock(old_pte - 1, old_ptl);
> if (anon_vma)
> - anon_vma_unlock_write(anon_vma);
> + anon_vma_unlock_read(anon_vma);
> if (mapping)
> mutex_unlock(&mapping->i_mmap_mutex);
> }
> @@ -199,12 +199,12 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
> vma);
> /* See comment in move_ptes() */
> if (need_rmap_locks)
> - anon_vma_lock_write(vma->anon_vma);
> + anon_vma_lock_read(vma->anon_vma);
> err = move_huge_pmd(vma, new_vma, old_addr,
> new_addr, old_end,
> old_pmd, new_pmd);
> if (need_rmap_locks)
> - anon_vma_unlock_write(vma->anon_vma);
> + anon_vma_unlock_read(vma->anon_vma);
> }
> if (err > 0) {
> need_flush = true;
> --
> 2.1.1
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