Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmasof a mergeable VMA

[Rik van Riel]

On 04/09/2010 07:56 PM, Linus Torvalds wrote:

> So _instead_ of all the patches that have floated about, I would suggest
> this simple change to "find_mergeable_anon_vma()" instead..

Boris, this is your chance to really ruin our week :)

If the bug persists with Linus's patch, we've been fixing
the wrong bug all week long, and you are experiencing
something else...

I'm getting really curious now.

> ---
>   mm/mmap.c |    6 ++++--
>   1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 75557c6..462a8ca 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -850,7 +850,8 @@ struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
>   	vm_flags = vma->vm_flags&  ~(VM_READ|VM_WRITE|VM_EXEC);
>   	vm_flags |= near->vm_flags&  (VM_READ|VM_WRITE|VM_EXEC);
>
> -	if (near->anon_vma&&  vma->vm_end == near->vm_start&&
> +	if (near->anon_vma&&  list_is_singular(&near->anon_vma_chain)&&
> +			vma->vm_end == near->vm_start&&
>    			mpol_equal(vma_policy(vma), vma_policy(near))&&
>   			can_vma_merge_before(near, vm_flags,
>   				NULL, vma->vm_file, vma->vm_pgoff +
> @@ -871,7 +872,8 @@ try_prev:
>   	vm_flags = vma->vm_flags&  ~(VM_READ|VM_WRITE|VM_EXEC);
>   	vm_flags |= near->vm_flags&  (VM_READ|VM_WRITE|VM_EXEC);
>
> -	if (near->anon_vma&&  near->vm_end == vma->vm_start&&
> +	if (near->anon_vma&&  list_is_singular(&near->anon_vma_chain)&&
> +			near->vm_end == vma->vm_start&&
>     			mpol_equal(vma_policy(near), vma_policy(vma))&&
>   			can_vma_merge_after(near, vm_flags,
>   				NULL, vma->vm_file, vma->vm_pgoff))

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