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

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Message-Id: <20100908124716.830a0055.akpm@linux-foundation.org>
Date:	Wed, 8 Sep 2010 12:47:16 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Gary King <gking@...dia.com>
Cc:	linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
	tj@...nel.org, linux-kernel@...r.kernel.org, stable@...nel.org,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH] bounce: call flush_dcache_page after bounce_copy_vec

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.

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