Re: X-freeze after clflush changes [Was: 2.6.23-rc6-mm1]

Jiri Slaby
2007-09-19T19:46:55Z

On 09/19/2007 09:24 PM, Andi Kleen wrote:
> On Wed, Sep 19, 2007 at 12:10:17PM -0700, Andrew Morton wrote:
>> On Wed, 19 Sep 2007 16:59:04 +0200 Jiri Slaby <jirislaby@gmail.com> wrote:
>>
>>> ---------8<---------8<---------8<---------8<---------8<---------8<----
>>> That means
>>> void agp_generic_destroy_page(void *addr)
>>> {
>>> struct page *page;
>>>
>>> if (addr == NULL)
>>> return;
>>>
>>> page = virt_to_page(addr);
>>> (1) unmap_page_from_agp(page);
>>> put_page(page);
>>> (2) free_page((unsigned long)addr);
>>> atomic_dec(&agp_bridge->current_memory_agp);
>>> }
>>>
>>> (1) unmap_page_from_agp -> change_page_attr -> change_page_attr_addr ->
>>> __change_page_attr -> save_page -> list_add(&fpage->lru, &deferred_pages);
>>> (2) free_page -> free_pages -> __free_pages -> free_hot_page ->
>>> free_hot_cold_page -> list_add(&page->lru, &pcp->list);
>> that'll hurt.
>>
>>> any ideas how to fix this?
>> We should hold a single reference on the page for its membership in
>> deferred_pages.
>
> The code is broken anyways. If you free pages without flushing
> them first some other innocent user allocating them will end up
> with possible uncached pages for some time.
>
> Does this simple patch help?

Yeah. (But X doesn't run -- this is maybe the known issue in this release).

> Flush uncached AGP pages before freeing
>
> Signed-off-by: Andi Kleen <ak@suse.de>

Tested-by: Jiri Slaby <jirislaby@gmail.com>

>
> Index: linux/drivers/char/agp/generic.c
> ===================================================================
> --- linux.orig/drivers/char/agp/generic.c
> +++ linux/drivers/char/agp/generic.c
> @@ -1185,6 +1185,7 @@ void agp_generic_destroy_page(void *addr
>
> page = virt_to_page(addr);
> unmap_page_from_agp(page);
> + flush_agp_mappings();
> put_page(page);
> free_page((unsigned long)addr);
> atomic_dec(&agp_bridge->current_memory_agp);
>

thanks,
--
Jiri Slaby (jirislaby@gmail.com)
Faculty of Informatics, Masaryk University