Messages in this thread Patch in this message | | | Date | Wed, 27 Jan 2010 09:56:14 -0800 | From | Stephen Hemminger <> | Subject | Re: Hang: 2.6.32.4 sky2/DMAR (was [PATCH] sky2: Fix WARNING: at lib/dma-debug.c:902 check_sync) |
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On Wed, 27 Jan 2010 11:57:35 -0500 Michael Breuer <mbreuer@majjas.com> wrote:
> On 1/27/2010 11:50 AM, Stephen Hemminger wrote: > > On Wed, 27 Jan 2010 10:34:51 -0500 > > Michael Breuer<mbreuer@majjas.com> wrote: > > > > > >> On 01/23/2010 06:21 PM, Jarek Poplawski wrote: > >> > >>> On Fri, Jan 22, 2010 at 06:50:21PM -0500, Michael Breuer wrote: > >>> > >>> > >>>> When the packets were dropped, there was a different sequence in the > >>>> log - DISCOVER/OFFER repeated. The "normal" is that the sequence > >>>> appeared correct and complete - DISCOVER/OFFER/REQUEST/ACK - or > >>>> INFORM/ACK (vs. INFORM repeatedly sans ACK) as the case may be. > >>>> > >>>> > >>> Anyway, I'd be intersted if the switch matters here. > >>> > >>> Plus one more test: could you try to load sky2 with the parameter: > >>> "copybreak=1" (the rest as in any recent test, which gave you dmar > >>> errors; any switch). > >>> > >>> Thanks, > >>> Jarek P. > >>> > >>> > >> Ok - now up 80+ hours with copybreak=1. I'm going to redo w/o copybreak > >> to confirm that I haven't inadvertently fixed something. However, given > >> that it might be copybreak-related, I looked at sky2.c again and I'm > >> wondering about the copybreak max size in sky2_rx_start: > >> > >> size = roundup(sky2->netdev->mtu + ETH_HLEN + VLAN_HLEN, 8); > >> > >> /* Stopping point for hardware truncation */ > >> thresh = (size - 8) / sizeof(u32); > >> > >> sky2->rx_nfrags = size>> PAGE_SHIFT; > >> BUG_ON(sky2->rx_nfrags> ARRAY_SIZE(re->frag_addr)); > >> > >> /* Compute residue after pages */ > >> size -= sky2->rx_nfrags<< PAGE_SHIFT; > >> > >> /* Optimize to handle small packets and headers */ > >> if (size< copybreak) > >> size = copybreak; > >> if (size< ETH_HLEN) > >> size = ETH_HLEN; > >> > >> > >> Why would increasing size to copybreak be valid here? > >> > >> Guessing a bit as I'm not sure about rx_nfrags, but if I read this > >> correctly, if size is ever less than copybreak it's because there isn't > >> enough space left for anything larger. If so, wouldn't increasing size > >> potentially corrupt something? I'd further guess that the resulting > >> condition manifests sooner (or at least with a more visible effect) when > >> using DMAR. > >> > >> In any event, why "copybreak" as the minimum buffer size? I'd suggest > >> that if it isn't possible to allocate at least MTU + overhead that > >> sky2_rx_start ought to be delayed until there is room. > >> > > This code is where driver decides how much data will be received in skb > > data area and the remaining data spills over into skb frags. > > Copybreak is the threshold so that packets less than size are copied > > to a new skb. The code doing the copying there assumes the data is > > totally contained in the skb (not in frags). The size increase there > > is to make sure that assumption is always true. I suppose you > > could do something perverse like setting copybreak really huge > > and confuse driver, but that is a user error. > > > > > Ok - but I'm wondering under what circumstances size would be < > copybreak in the first place after computing the residue. If size ends > up being unreasonably small, is simply increasing the number to whatever > copybreak is correct? Assuming my testing is correct, then the crash > I've been experiencing when using dmar (only) seems related to the value > of copybreak. I don't think the other use (skb reuse) is the issue (but > hey, I could have missed something). The crash occurs when copybreak is > the default of 128, didn't happen when I set copybreak to 1.
Does this change it? If so the dma code is (not sky2) is buggy and not rounding up properly.
--- a/drivers/net/sky2.c 2010-01-27 09:46:10.940005248 -0800 +++ b/drivers/net/sky2.c 2010-01-27 09:53:47.141267850 -0800 @@ -2257,13 +2257,16 @@ static struct sk_buff *receive_copy(stru skb = netdev_alloc_skb_ip_align(sky2->netdev, length); if (likely(skb)) { + unsigned dma_align = dma_get_cache_alignment(); + unsigned dma_size = ALIGN(length+1, dma_align); + pci_dma_sync_single_for_cpu(sky2->hw->pdev, re->data_addr, - length, PCI_DMA_FROMDEVICE); + dma_size, PCI_DMA_FROMDEVICE); skb_copy_from_linear_data(re->skb, skb->data, length); skb->ip_summed = re->skb->ip_summed; skb->csum = re->skb->csum; pci_dma_sync_single_for_device(sky2->hw->pdev, re->data_addr, - length, PCI_DMA_FROMDEVICE); + dma_size, PCI_DMA_FROMDEVICE); re->skb->ip_summed = CHECKSUM_NONE; skb_put(skb, length); }
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