linux-kernel - Re: [PATCH 5/5] uprobes: kill insert_vm_struct()->uprobe

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Date:	Fri, 13 Jul 2012 13:41:03 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] uprobes: kill insert_vm_struct()->uprobe_mmap()

* Oleg Nesterov <oleg@...hat.com> [2012-07-08 22:30:11]:

> Kill insert_vm_struct()->uprobe_mmap(). It is not needed, nobody
> except arch/ia64/kernel/perfmon.c uses insert_vm_struct(vma) with
> vma->vm_file != NULL.
> 

Right, but somebody else might start using this later.
I cant think of a use case though.

> And it is wrong. Again, get_user_pages() can not succeed before
> vma_link(vma) makes is visible to find_vma(). And even if this
> worked, we must not insert the new bp before this mapping is
> visible to vma_prio_tree_foreach() for uprobe_unregister().
> 

Agree, we are wrong to do it before vma_link.


> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  mm/mmap.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index e5a4614..4fe2697 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2345,9 +2345,6 @@ int insert_vm_struct(struct mm_struct * mm, struct vm_area_struct * vma)
>  	     security_vm_enough_memory_mm(mm, vma_pages(vma)))
>  		return -ENOMEM;
> 
> -	if (vma->vm_file && uprobe_mmap(vma))
> -		return -EINVAL;
> -
>  	vma_link(mm, vma, prev, rb_link, rb_parent);
>  	return 0;
>  }

Can we do something like:

	vma_link(mm, vma, prev, rb_link, rb_parent);

	if (vma->vm_file && uprobe_mmap(vma)) {
		/* FIXME: dont know if calling unmap_region is fine here */
		unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end); 
		return -EINVAL;
	}

	return 0;

}

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