linux-kernel - Re: Possible RAID6 regression with ASYNC_TX

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Message-ID: <20150512125546.GJ10961@lukather>
Date:	Tue, 12 May 2015 14:55:46 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Shaohua Li <shli@...nel.org>
Cc:	Neil Brown <neilb@...e.de>, linux-raid@...r.kernel.org,
	linux-kernel@...r.kernel.org, Lior Amsalem <alior@...vell.com>,
	Thomas Petazzoni <thomas@...e-electrons.com>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Boris Brezillon <boris@...e-electrons.com>
Subject: Re: Possible RAID6 regression with ASYNC_TX_DMA enabled in 4.1

Hi Shaohua,

On Sun, May 10, 2015 at 11:26:38PM -0700, Shaohua Li wrote:
> 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.
> > 
> > http://code.bulix.org/eh8iew-88342?raw
> > 
> > It seems to be generated by that warning here:
> > 
> > http://lxr.free-electrons.com/source/crypto/async_tx/async_tx.c#L173
> > 
> > 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.

The error indeed disappears if stripe_can_batch always returns false.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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