Re: [PATCH] fix rmap walk during fork

[Hugh Dickins <hughd@google.com>]

On Wed, 15 Sep 2010, Andrea Arcangeli wrote:

> From: Andrea Arcangeli <aarcange@redhat.com>
> 
> The below bug in fork lead to the rmap walk finding the parent huge-pmd twice
> instead of just one, because the anon_vma_chain objects of the child vma still
> point to the vma->vm_mm of the parent. The below patch fixes it by making the
> rmap walk accurate during fork. It's not a big deal normally but it
> worth being accurate considering the cost is the same.
> 
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>

Acked-by: Hugh Dickins <hughd@google.com>

> ---
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -360,10 +360,10 @@ static int dup_mmap(struct mm_struct *mm
>  		if (IS_ERR(pol))
>  			goto fail_nomem_policy;
>  		vma_set_policy(tmp, pol);
> +		tmp->vm_mm = mm;
>  		if (anon_vma_fork(tmp, mpnt))
>  			goto fail_nomem_anon_vma_fork;
>  		tmp->vm_flags &= ~VM_LOCKED;
> -		tmp->vm_mm = mm;
>  		tmp->vm_next = tmp->vm_prev = NULL;
>  		file = tmp->vm_file;
>  		if (file) {

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