linux-kernel - Re: bisected regression: 3c59x corrupts packets in 3.17-rc5

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Date:	Tue, 16 Sep 2014 10:31:22 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Meelis Roos <mroos@...ux.ee>
Cc:	Steffen Klassert <steffen@...ssert.de>, netdev@...r.kernel.org,
	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: bisected regression: 3c59x corrupts packets in 3.17-rc5

On Tue, Sep 16, 2014 at 01:32:31PM +0300, Meelis Roos wrote:
> [ Fixed Steffen Klasserts bouncing email address as per the bounce message ]
> 
> > > Somewhere between 3.17.0-rc3 and 3.17.0-rc5 I started seeing dropped ssh 
> > > connections to a couple of test servers with dual AthlonMP (32-bit) and 
> > > 3C90x family of NICs (3Com Corporation 3c980-C 10/100baseTX NIC 
> > > [Python-T] (rev 78) in one server and 3Com Corporation 3c905C-TX/TX-M 
> > > [Tornado] (rev 78) in the other server). Bisect leads to the following 
> > > commit:
> > > 
> > > 98ea232cf63961fad734cc8c5e07e8915ec73073 is the first bad commit
> > > commit 98ea232cf63961fad734cc8c5e07e8915ec73073
> > > Author: Neil Horman <nhorman@...driver.com>
> > > Date:   Thu Sep 4 06:13:38 2014 -0400
> > > 
> > >     3c59x: avoid panic in boomerang_start_xmit when finding page address:
> > >     ...
> > > 
> > I'm guessing the above change has uncovered another bug, mostly likely an
> > exhaustion of dma space on your system.  Nothing in the transmit path there does
> > any error checking for successful dma mapping, which it really should.  I'd be
> > willing to be that any dma mapping error leads to a leak in the mapping table.
> > Does your system have an iommu, or does it use swiotlb?  If its the latter, can
> > you increase the swiotlb table space and see if that relieves the problem?  In
> > the interim, I'll start adding some error checking to the transmit path.
> 
> # CONFIG_IOMMU_SUPPORT is not set
> 
> nothing matching iommu or iotlb in dmesg. I thought the system does not 
> have any - K7 CPUs and AMD 760MP chipset with normal AGP gart.
> 
> [    3.763519] agpgart-amdk7 0000:00:00.0: AMD 760MP chipset
> [    3.782995] agpgart-amdk7 0000:00:00.0: AGP aperture is 64M @ 0xf8000000
> 
Then I think you are likely very lmiited in how much DMA memory you can map (may
be limited to ZONE_DMA), which is likely from where this problem is stemming.
Try adding swiotlb= setup to the kernel command line and play with the size to
see if you can avoid the problem.  I also have a patch I'm sending you to test.

Neil

> -- 
> Meelis Roos (mroos@...ux.ee)
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