linux-kernel - Re: [PATCH] bounce: call flush_dcache_page after bounce_copy

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Message-ID: <4C87E8D2.4050005@kernel.dk>
Date:	Wed, 08 Sep 2010 21:49:38 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Gary King <gking@...dia.com>, linux-mm@...ck.org,
	linux-arm-kernel@...ts.infradead.org, tj@...nel.org,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH] bounce: call flush_dcache_page after bounce_copy_vec

On 09/08/2010 09:47 PM, Andrew Morton wrote:
> On Tue,  7 Sep 2010 13:45:34 -0700
> Gary King <gking@...dia.com> wrote:
> 
>> I have been seeing problems on Tegra 2 (ARMv7 SMP) systems with HIGHMEM
>> enabled on 2.6.35 (plus some patches targetted at 2.6.36 to perform
>> cache maintenance lazily), and the root cause appears to be that the
>> mm bouncing code is calling flush_dcache_page before it copies the
>> bounce buffer into the bio.
>>
>> The patch below reorders these two operations, and eliminates numerous
>> arbitrary application crashes on my dev system.
>>
>> Gary
>>
>> --
>> >From 678c9bca8d8a8f254f28af91e69fad3aa1be7593 Mon Sep 17 00:00:00 2001
>> From: Gary King <gking@...dia.com>
>> Date: Mon, 6 Sep 2010 15:37:12 -0700
>> Subject: bounce: call flush_dcache_page after bounce_copy_vec
>>
>> the bounced page needs to be flushed after data is copied into it,
>> to ensure that architecture implementations can synchronize
>> instruction and data caches if necessary.
>>
>> Signed-off-by: Gary King <gking@...dia.com>
>> ---
>>  mm/bounce.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/mm/bounce.c b/mm/bounce.c
>> index 13b6dad..1481de6 100644
>> --- a/mm/bounce.c
>> +++ b/mm/bounce.c
>> @@ -116,8 +116,8 @@ static void copy_to_high_bio_irq(struct bio *to, struct bio *from)
>>  		 */
>>  		vfrom = page_address(fromvec->bv_page) + tovec->bv_offset;
>>  
>> -		flush_dcache_page(tovec->bv_page);
>>  		bounce_copy_vec(tovec, vfrom);
>> +		flush_dcache_page(tovec->bv_page);
>>  	}
>>  }
> 
> Oh my, that was bad.

Indeed, I wonder how that could have been wrong for so long.

> I queued your fix for 2.6.36 and tagged it for -stable backporting,
> thanks.

Thanks, you can add my acked-by.

-- 
Jens Axboe

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