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

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Message-ID: <20070919192453.GB18707@one.firstfloor.org>
Date:	Wed, 19 Sep 2007 21:24:53 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jiri Slaby <jirislaby@...il.com>, linux-kernel@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: X-freeze after clflush changes [Was: 2.6.23-rc6-mm1]

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? 

-Andi


Flush uncached AGP pages before freeing

Signed-off-by: Andi Kleen <ak@...e.de>

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);
-
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