linux-kernel - Re: [patch 2.6.27-rc3] at91_mci: don't use coherent dma buffers

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Date:	Fri, 22 Aug 2008 09:40:00 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	David Brownell <david-b@...bell.net>,
	Pierre Ossman <drzeus-mmc@...eus.cx>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	lkml <linux-kernel@...r.kernel.org>,
	Andrew Victor <linux@...im.org.za>,
	Russell King <rmk@....linux.org.uk>
Subject: Re: [patch 2.6.27-rc3] at91_mci: don't use coherent dma buffers

Pierre, Andrew,

You can add my...

David Brownell :
> From: David Brownell <dbrownell@...rs.sourceforge.net>
> 
> At91_mci is abusing dma_free_coherent(), which may not be called
> with IRQs disabled.  I saw "mkfs.ext3" on an MMC card objecting
> voluminously as each write completed:
> 
>  WARNING: at arch/arm/mm/consistent.c:368 dma_free_coherent+0x2c/0x224()
>  [<c002726c>] (dump_stack+0x0/0x14) from [<c00387d4>] (warn_on_slowpath+0x4c/0x68)
>  [<c0038788>] (warn_on_slowpath+0x0/0x68) from [<c0028768>] (dma_free_coherent+0x2c/0x224)
>   r6:00008008 r5:ffc06000 r4:00000000
>  [<c002873c>] (dma_free_coherent+0x0/0x224) from [<c01918ac>] (at91_mci_irq+0x374/0x420)
>  [<c0191538>] (at91_mci_irq+0x0/0x420) from [<c0065d9c>] (handle_IRQ_event+0x2c/0x6c)
>  ...
> 
> This bug has been around for a LONG time.  The MM warning is
> from late 2005, but the driver merged a year later ... so I'm
> puzzled why nobody noticed this before now.
> 
> The fix involves noting that this buffer shouldn't be DMA-coherent;
> it's just used for normal DMA writes.  So replace it with standard
> kmalloc() buffering and DMA mapping calls.
> 
> This is the quickie fix.  A better one would not rely on allocating
> large bounce buffers.  (Note that dma_alloc_coherent could have failed
> too, but that case was ignored... kmalloc is a bit more likely to
> fail though.)
> 
> Signed-off-by: David Brownell <dbrownell@...rs.sourceforge.net>

...

Signed-off-by: Nicolas Ferre <nicolas.ferre@...el.com>


-- 
Nicolas Ferre

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