Re: [PATCH V1 2/2] mm: Wrap calls to set_pte_at_notify with invalidate_range_start and invalidate_range_end

[Andrew Morton <akpm@linux-foundation.org>]

On Tue,  4 Sep 2012 11:41:21 +0300
Haggai Eran <haggaie@mellanox.com> wrote:

> In order to allow sleeping during invalidate_page mmu notifier calls, we
> need to avoid calling when holding the PT lock. In addition to its
> direct calls, invalidate_page can also be called as a substitute for a
> change_pte call, in case the notifier client hasn't implemented
> change_pte.
> 
> This patch drops the invalidate_page call from change_pte, and instead
> wraps all calls to change_pte with invalidate_range_start and
> invalidate_range_end calls.
> 
> Note that change_pte still cannot sleep after this patch, and that
> clients implementing change_pte should not take action on it in case the
> number of outstanding invalidate_range_start calls is larger than one,
> otherwise they might miss a later invalidation.
> 
> ...
>
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -145,6 +145,7 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>  	/* For try_to_free_swap() and munlock_vma_page() below */
>  	lock_page(page);
>  
> +	mmu_notifier_invalidate_range_start(mm, addr, addr + PAGE_SIZE);
>  	err = -EAGAIN;
>  	ptep = page_check_address(page, mm, addr, &ptl, 0);
>  	if (!ptep)
> @@ -173,6 +174,7 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
>  
>  	err = 0;
>   unlock:
> +	mmu_notifier_invalidate_range_end(mm, addr, addr + PAGE_SIZE);
>  	unlock_page(page);
>  	return err;
>  }

Again, now I have to apply the patch and peer at the code to work out
whether `addr' got changed anywhere between these two calls.  And I
somehow need to ensure that `addr' will not get modified in the future
and I can't do that!

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