linux-kernel - Re: [PATCH] raid5: panic() on dma_wait_for_async

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Message-ID: <20121119120632.1c97e306@notabene.brown>
Date:	Mon, 19 Nov 2012 12:06:32 +1100
From:	NeilBrown <neilb@...e.de>
To:	Dan Williams <djbw@...com>
Cc:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	Vinod Koul <vinod.koul@...el.com>,
	Tomasz Figa <t.figa@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>
Subject: Re: [PATCH] raid5: panic() on dma_wait_for_async_tx() error


Hi Dan,
 could you comment on this please?  Would it make sense to arrange for errors
 to propagate up?  Or should we arrange to do a software-fallback in the dma
 engine is a problem?  What sort of things can cause error here anyway?

Thanks,
NeilBrown



On Thu, 08 Nov 2012 12:20:55 +0100 Bartlomiej Zolnierkiewicz
<b.zolnierkie@...sung.com> wrote:

> On Thursday 08 November 2012 12:15:26 Alan Cox wrote:
> > On Thu, 08 Nov 2012 11:06:29 +0100
> > Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com> wrote:
> > 
> > > From: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
> > > Subject: [PATCH] raid5: panic() on dma_wait_for_async_tx() error
> > > 
> > > There is not much we can do on dma_wait_for_async_tx() error
> > > so just panic() for now.
> > > 
> > > Cc: Neil Brown <neilb@...e.de>
> > > Cc: Vinod Koul <vinod.koul@...el.com>
> > > Cc: Dan Williams <djbw@...com>
> > > Cc: Tomasz Figa <t.figa@...sung.com>
> > > Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
> > > Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
> > > ---
> > >  drivers/md/raid5.c |    4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > Index: b/drivers/md/raid5.c
> > > ===================================================================
> > > --- a/drivers/md/raid5.c	2012-11-07 16:25:19.480876012 +0100
> > > +++ b/drivers/md/raid5.c	2012-11-07 16:27:46.244875992 +0100
> > > @@ -3223,7 +3223,9 @@ static void handle_stripe_expansion(stru
> > >  	/* done submitting copies, wait for them to complete */
> > >  	if (tx) {
> > >  		async_tx_ack(tx);
> > > -		dma_wait_for_async_tx(tx);
> > > +		if (dma_wait_for_async_tx(tx) != DMA_SUCCESS)
> > > +			panic("%s: DMA error waiting for transaction\n",
> > > +			      __func__);
> > 
> > Thats a really horrible place to panic.
> 
> Still it seems better thing to do than silently ignoring errors
> and trying to continue operations with inconsistent data.
> 
> Unfortunately higher-layers don't support error conditions and
> fixing them seems to be non-trivial task.
> 
> Best regards,
> --
> Bartlomiej Zolnierkiewicz
> Samsung Poland R&D Center
> --
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