linux-kernel - Re: [PATCH] Fix kunmap() argument in sg_miter

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Date:	Mon, 17 Nov 2008 09:35:00 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...e.hu>, Jens Axboe <jens.axboe@...cle.com>,
	Tejun Heo <htejun@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Hugh Dickins <hugh@...itas.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] Fix kunmap() argument in sg_miter_stop

Linus Torvalds wrote:
> On Mon, 17 Nov 2008, Jeremy Fitzhardinge wrote:
>
>   
>> Pass the struct page * to kunmap, not the vaddr of the mapping itself.
>>
>> Pointed out by Jens Axboe <jens.axboe@...cle.com>
>>
>> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
>> ---
>> drivers/xen/balloon.c |    2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> ===================================================================
>> --- a/drivers/xen/balloon.c
>> +++ b/drivers/xen/balloon.c
>> @@ -120,7 +120,7 @@
>> 	if (PageHighMem(page)) {
>> 		void *v = kmap(page);
>> 		clear_page(v);
>> -		kunmap(v);
>> +		kunmap(page);
>> 	} else {
>> 		void *v = page_address(page);
>> 		clear_page(v);
>>     
>
> Well, quite frankly, the whole thing looks like crud.
>
> First off, 'kmap/kunmap' work on regular pages too. So if you're highmem 
> aware, you should just do
>
> 	void *v = kmap(page);
> 	clear_page(v);
> 	kunmap(page);
>
> and be done with it. 
>
> Secondly, we actually have a function called "clear_highpage()" that does 
> this, except it uses kmap_atomic(page, KM_USER0). Which is _probably 
> better anyway, but I didn't check if there is some magical reason why it 
> wouldn't work.
>   

OK.

Subject: xen/balloon: use clear_highpage()

Just use clear_highpage() rather than reimplementing it poorly.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 drivers/xen/balloon.c |    9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

===================================================================
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -122,14 +122,7 @@
 static void scrub_page(struct page *page)
 {
 #ifdef CONFIG_XEN_SCRUB_PAGES
-	if (PageHighMem(page)) {
-		void *v = kmap(page);
-		clear_page(v);
-		kunmap(v);
-	} else {
-		void *v = page_address(page);
-		clear_page(v);
-	}
+	clear_highpage(page);
 #endif
 }
 



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