Re: [Xen-devel] [PATCH] fix page_list_splice()

[Keir Fraser <keir@xxxxxxx>]

On 06/06/2012 09:23, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> Other than in __list_splice(), the first element's prev pointer doesn't
> need adjustment here - it already is PAGE_LIST_NULL. Rather than fixing
> the assignment (to formally match __list_splice()), simply assert that
> this assignment is really unnecessary.
>
> Reported-by: Jisoo Yang <jisooy@xxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> --- a/xen/include/xen/mm.h
> +++ b/xen/include/xen/mm.h
> @@ -270,7 +270,8 @@ page_list_splice(struct page_list_head *
>      last = list->tail;
>      at = head->next;
>  
> -    first->list.prev = page_to_pdx(head->next);
> +    /* Both first->list.prev and at->list.prev are PAGE_LIST_NULL. */

ASSERT(first->list.prev == PAGE_LIST_NULL); ?

It seems odd to have one assumption encoded as an ASSERTion, and one as a
code comment... A second assertion makes the assumption explicit, and
run-time checked in debug builds.

 -- Keir

> +    ASSERT(first->list.prev == at->list.prev);
>      head->next = first;
>  
>      last->list.next = page_to_pdx(at);
> 
> 
> 
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> http://lists.xen.org/xen-devel



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