linux-ext4 - Re: Rampant ext3/4 corruption on 2.6.34-rc7 with VIVT ARM (Marvell 88f5182)

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Date:	Thu, 13 May 2010 14:42:31 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	saeed@...vell.com, nico@...vell.com, jamie@...reable.org,
	linux-kernel@...r.kernel.org, jejb@...isc-linux.org,
	santosh.shilimkar@...com, akpm@...ux-foundation.org,
	linux-ext4@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: Rampant ext3/4 corruption on 2.6.34-rc7 with VIVT ARM (Marvell
 88f5182)

On Thu, 2010-05-13 at 12:12 +0900, FUJITA Tomonori wrote:
> X86 OOSTORE uses a memory barrier dma_sync_single_for_device (seems
> that some mips archs also use it and do cache operations).
> 
> I think that the DMA-API says that
> 
> - dma_sync_single_for_device() makes sure the data ready for DMA.
> 
> - dma_sync_single_for_cpu() makes sure that drivers doesn't get the
>   stale data after DMA.
> 
> I guess, it means if an architecture need a memory barrier (not only
> cache operations) to guarantee the above, the architecture needs to
> take care of it. 

Right, but doing an indirect function pointer call for a memory barrier
in what can be a pretty hot code path doesn't sound like a great idea
if it can be avoided. I'd rather we define some inline that the arch
can stick in there if it wishes so.

Cheers,
Ben.


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