Re: [RFC PATCH] take all anon_vma locks in anon_vma_lock

[Rik van Riel]

On 04/28/2010 02:03 PM, Andrea Arcangeli wrote:
> On Wed, Apr 28, 2010 at 01:47:19PM -0400, Rik van Riel wrote:
> >   static inline void anon_vma_unlock(struct vm_area_struct *vma)
>
> never mind as this is RFC, lock is clear enough
>
> > @@ -1762,7 +1760,8 @@ static int expand_downwards(struct vm_area_struct *vma,
> >   	if (error)
> >   		return error;
> >
> > -	anon_vma_lock(vma);
> > +	spin_lock(&mm->page_table_lock);
> > +	anon_vma_lock(vma,&mm->page_table_lock);
>
> This will cause a lock inversion (page_table_lock can only be taken
> after the anon_vma lock). I don't immediately see why the
> page_table_lock here though?

We need to safely walk the vma->anon_vma_chain /
anon_vma_chain->same_vma list.

So much for using the mmap_sem for read + the
page_table_lock to lock the anon_vma_chain list.

We'll need a new lock somewhere, probably in the
mm_struct since one per process seems plenty.

I'll add that in the next version of the patch.

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