Re: [PATCH v2] tmio_mmc_dma: fix PIO fallback on SDHI

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 08/04/2013 06:10 PM, Sergei Shtylyov wrote:

>>> I'm testing SH-Mobile SDHI driver in DMA mode with  a new DMA controller
>>> using
>>> 'bonnie++' and getting DMA error after which the tmio_mmc_dma.c code falls
>>> back
>>> to PIO but all commands time out after that.  It turned out that the fallback
>>> code calls tmio_mmc_enable_dma() with RX/TX channels already freed and
>>> pointers
>>> to them cleared, so that the function bails out early instead  of clearing the
>>> DMA bit in the CTL_DMA_ENABLE register. The regression was introduced by
>>> commit
>>> 162f43e31c5a376ec16336e5d0ac973373d54c89 (mmc: tmio: fix a deadlock).
>>> Moving tmio_mmc_enable_dma() calls to the top of the PIO fallback code in
>>> tmio_mmc_start_dma_{rx|tx}() helps.

>>> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
>>> Cc: stable@vger.kernel.org # 3.1+

>> Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>

>> Not sure though how far back in stable this really has to go. We don't
>> have any real-life problem reports with older kernels, do we?

>     If we did, that error would have been fixed earlier, wouldn't it?

>> I think
>> approach to which patches should get into stable changed recently.

>     Haven't heard about that (or seen any change in the policy). The issue
> with this bug is its catastrophic consequencies: you can hardly ^C or ^Z out
> of 'bonnie++' when it happens (in fact, you cannot ^C at all). IIRC you can't
> even kill it from another shell.

    Yeah, and the filesystem is seriously corrupt after this (I've tested only 
on VFAT so far).

>> Thanks
>> Guennadi

WBR, Sergei