Re: [RFC][PATCH 9/7] mm: fix mm_take_all_locks() locking order

[Hugh Dickins <hugh@veritas.com>]

On Thu, 7 Aug 2008, Peter Zijlstra wrote:
> 
> Which the locking hierarchy in mm/rmap.c confirms as 'valid'.
> 
> Although I don't think there are any users of these two locks that don't
> hold the mmap_sem, therefore the nesting is strictly ok, but since we
> already have an established order, we might as well respect it.

Yes, I agree.

> Fix this by first taking all the mapping->i_mmap_lock instances and then
> take all anon_vma->lock instances.

Okay.  I'd have preferred taking anon_vma lock after i_mmap_lock
each time around the loop, but imagine that's just as problematic
for lockdep as the original.

> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

Acked-by: Hugh Dickins <hugh@veritas.com>

> ---
>  mm/mmap.c |   10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/mm/mmap.c
> ===================================================================
> --- linux-2.6.orig/mm/mmap.c
> +++ linux-2.6/mm/mmap.c
> @@ -2358,11 +2358,17 @@ int mm_take_all_locks(struct mm_struct *
>  	for (vma = mm->mmap; vma; vma = vma->vm_next) {
>  		if (signal_pending(current))
>  			goto out_unlock;
> -		if (vma->anon_vma)
> -			vm_lock_anon_vma(mm, vma->anon_vma);
>  		if (vma->vm_file && vma->vm_file->f_mapping)
>  			vm_lock_mapping(mm, vma->vm_file->f_mapping);
>  	}
> +
> +	for (vma = mm->mmap; vma; vma = vma->vm_next) {
> +		if (signal_pending(current))
> +			goto out_unlock;
> +		if (vma->anon_vma)
> +			vm_lock_anon_vma(mm, vma->anon_vma);
> +	}
> +
>  	ret = 0;
>  
>  out_unlock: