Re: Possible RAID6 regression with ASYNC_TX_DMA enabled in 4.1

From: Shaohua Li
Date: Mon May 11 2015 - 12:12:59 EST

On Thu, May 07, 2015 at 02:57:02PM +0200, Maxime Ripard wrote:
> Hi,
> I'm currently trying to add support for the PQ operations on the
> marvell XOR engine, in dmaengine, obviously to be able to use async_tx
> to offload these operations.
> I'm testing these patches with a RAID6 array with 4 disks.
> However, since the commit 59fc630b8b5f ("RAID5: batch adjacent full
> stripe write", every write to that array fails with the following
> stacktrace.
> It seems to be generated by that warning here:
> And indeed, if we dump the status of depend_tx here, it's already been
> acked.
> That doesn't happen if ASYNC_TX_DMA is disabled, hence using the
> software version of it, instead of relying on our XOR engine. It
> doesn't happen on any commit prior to the one mentionned above, with
> the exact same changes applied. These changes are meant to be
> contributed, so I can definitely push them somewhere if needed.
> I don't really know where to look for though, the change that is
> causing this is probably the change in ops_run_reconstruct6, but I'm
> not sure that this partial revert alone would work with regard to the
> rest of the patch.

I don't have a machine with dmaengine, it's likely there is error in this side.
Could you please make stripe_can_batch() returns false always and check if the
error disappear? This should narrow down if it's related to batch issue.

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