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

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Date:	Wed, 19 Sep 2007 21:46:41 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: X-freeze after clflush changes [Was: 2.6.23-rc6-mm1]

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@...il.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@...e.de>

Tested-by: Jiri Slaby <jirislaby@...il.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@...il.com)
Faculty of Informatics, Masaryk University
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