On Tue, 2012-11-20 at 09:18 +1100, NeilBrown wrote:
> On Mon, 19 Nov 2012 05:22:25 +0000 Dan Williams <djbw@xxxxxx> wrote:
>
> >
> >
> > On 11/18/12 5:06 PM, "NeilBrown" <neilb@xxxxxxx> 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.
> >
>
> So maybe I could:
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index ac09fa4..ffbf0ca 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -3268,7 +3268,7 @@ static void handle_stripe_expansion(struct r5conf *conf, struct stripe_head *sh)
> /* done submitting copies, wait for them to complete */
> if (tx) {
> async_tx_ack(tx);
> - dma_wait_for_async_tx(tx);
> + async_tx_quiesce(&tx);
> }
> }
>
>
>
> and then the panic would be somebody else's problem?
>
> I note that handle_stripe_expansion has:
>
> async_tx_ack(tx);
> dma_wait_for_async_tx(tx);
>
> while async_tx_quiesce() has:
>
> if (dma_wait_for_async_tx(*tx) == DMA_ERROR)
> panic("DMA_ERROR waiting for transaction\n");
> async_tx_ack(*tx);
>
>
> i.e. the same two functions called in the reverse order. Is the order
> important? Is handle_stripe_expansion wrong? Should the patch I apply
> actually be:
>
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index ac09fa4..e51d903 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -3266,10 +3266,7 @@ static void handle_stripe_expansion(struct r5conf *conf, struct stripe_head *sh)
>
> }
> /* done submitting copies, wait for them to complete */
> - if (tx) {
> - async_tx_ack(tx);
> - dma_wait_for_async_tx(tx);
> - }
> + async_tx_quiesce(&tx);
> }
>
Yes, this one, handles it like the other cases of needing to do a
synchronous wait and does not care if tx is NULL.
--
Dan
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