Re: Possible RAID6 regression with ASYNC_TX_DMA enabled in 4.1

[Shaohua Li <shli@kernel.org>]

On Tue, May 12, 2015 at 02:55:46PM +0200, Maxime Ripard wrote:
> 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.

Does this fix it?


diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 77dfd72..5e820fc 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -1825,7 +1825,7 @@ ops_run_reconstruct6(struct stripe_head *sh, struct raid5_percpu *percpu,
 	} else
 		init_async_submit(&submit, 0, tx, NULL, NULL,
 				  to_addr_conv(sh, percpu, j));
-	async_gen_syndrome(blocks, 0, count+2, STRIPE_SIZE,  &submit);
+	tx = async_gen_syndrome(blocks, 0, count+2, STRIPE_SIZE,  &submit);
 	if (!last_stripe) {
 		j++;
 		sh = list_first_entry(&sh->batch_list, struct stripe_head,