linux-kernel - Re: [PATCH 4/5] uprobes: kill copy_vma()->uprobe

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Date:	Fri, 13 Jul 2012 13:43:33 +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 4/5] uprobes: kill copy_vma()->uprobe_mmap()

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

> Kill copy_vma()->uprobe_mmap(new_vma), it is absolutely wrong.
> 
> This new_vma was just initialized to represent the new unmapped area,
> [vm_start, vm_end) was returned by get_unmapped_area() in the caller.
> 
> This means that uprobe_mmap()->get_user_pages() will fail for sure,
> simply because find_vma() can never succeed. And I verified that
> sys_mremap()->mremap_to() indeed always fails with the wrong ENOMEM
> code if [addr, addr+old_len] is probed.
> 
> And why this uprobe_mmap() was added? I believe the intent was wrong.
> Note that the caller is going to do move_page_tables(), all registered
> uprobes are already faulted in, we only change the virtual addresses.
> 
> NOTE: However, somehow we need to close the race with uprobe_register()
> which relies on map_info->vaddr. This needs another fix I'll try to do
> later. Probably we need uprobe_mmap() in move_vma() but we can not do
> this right now, this can confuse uprobes_state.counter (which I still
> hope we are going to kill).
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

> ---
>  mm/mmap.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 3edfcdf..e5a4614 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2418,9 +2418,6 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
>  			if (new_vma->vm_file) {
>  				get_file(new_vma->vm_file);
> 
> -				if (uprobe_mmap(new_vma))
> -					goto out_free_mempol;
> -
>  				if (vma->vm_flags & VM_EXECUTABLE)
>  					added_exe_file_vma(mm);
>  			}
> -- 
> 1.5.5.1
> 

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