Re: [patch] mm: fix anon_vma races

[Hugh Dickins <hugh@veritas.com>]

On Sat, 18 Oct 2008, Peter Zijlstra wrote:
> 
> fault_creation:
> 
>  anon_vma_prepare()
>  page_add_new_anon_rmap();
> 
> expand_creation:
> 
>  anon_vma_prepare()
>  anon_vma_lock();
> 
> rmap_lookup:
> 
>  page_referenced()/try_to_unmap()
>    page_lock_anon_vma()
> 
> vma_lookup:
> 
>  vma_adjust()/vma_*
>    vma->anon_vma
> 
> teardown:
> 
>  unmap_vmas()
>    zap_range()
>       page_remove_rmap()
>       free_page()
>  free_pgtables()
>    anon_vma_unlink()
>    free_range()
>   
> IOW we remove rmap, free the page (set mapping=NULL) and then unlink and
> free the anon_vma.
> 
> But at that time vma->anon_vma is still set.
> 
> 
> head starts to hurt,.. 

Comprehension isn't my strong suit at the moment: I don't grasp
what problem you're seeing here - if you can spell it out in more
detail for me, I'd like to try stopping your head hurt - though not
at cost of making mine hurt more!

Hugh

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