Re: [PATCH 2/5] uprobes: __replace_page() should not usepage_address_in_vma()

[Srikar Dronamraju]

* Oleg Nesterov <oleg@xxxxxxxxxx> [2012-06-19 21:47:12]:

> page_address_in_vma(old_page) in __replace_page() is ugly and wrong.
> The caller already knows the correct virtual address, this page was
> found by get_user_pages(vaddr).
> 
> However, page_address_in_vma() can actually fail if page->mapping was
> cleared by __delete_from_page_cache() after get_user_pages() returns.
> But this means the race with page reclaim, write_opcode() should not
> fail, it should retry and read this page again. Not sure this race is
> really possible though, page_freeze_refs() logic should prevent it.
> 
> We could change __replace_page() to return -EAGAIN in this case, but
> it would be better to simply use the caller's vaddr and rely on
> page_check_address().
> 
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> ---
>  kernel/events/uprobes.c |   10 +++-------
>  1 files changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index a2b32a5..5b10705 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -132,17 +132,13 @@ static loff_t vma_address(struct vm_area_struct *vma, loff_t offset)
>   *
>   * Returns 0 on success, -EFAULT on failure.
>   */
> -static int __replace_page(struct vm_area_struct *vma, struct page *page, struct page *kpage)
> +static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
> +				struct page *page, struct page *kpage)

Could please update the comment above __replace_page to mention that it
now takes addr as a parameter?

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