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

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Date:	Mon, 19 Nov 2012 05:22:25 +0000
From:	Dan Williams <djbw@...com>
To:	NeilBrown <neilb@...e.de>
CC:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-raid@...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

On 11/18/12 5:06 PM, "NeilBrown" <neilb@...e.de> wrote:

>
>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?

Propagating up is missing reliable "dma abort" operation.

In these cases the engine failed to complete due to hardware hang / driver
bug, or has hit a memory error (uncorrectable even with software
fallback).  This originally should have been using async_tx_quiesce()
which also does the panic.

The engines that I have worked with have either lacked support for
aborting, or were otherwise unable to recover from a hardware hang.
However, for engines that do support error recovery they should be able to
hide the failure from the upper layers.

--
Dan

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