So much for THAT theory...

And now for something completely different.

I had set up netconsole to monitor BH's problem remotely. Netconsole sends debugging messages across the network to another system so you can see what's happening up to the moment of a crash.

And here we have it:

hda: ide_dma_sff_timer_expiry: DMA status (0x20)
hda: DMA timeout retryhda: timeout waiting for DMA
hda: DMA timeout: status=0x58 { DriveReady SeekComplete DataRequest }
hda: possibly failed opcode: 0x35
hda: status error: status=0x58 { DriveReady SeekComplete DataRequest }
hda: possibly failed opcode: 0x35
hda: drive not ready for command
ide0: reset: success

It's not a NIC driver issue after all. It's the drive hanging. Or rather, some kind of DMA issue with the drive and the controller.

So it's back to the drawing board.

But right now I have shut off DMA on the drive manually, so I expect things to be OK while I re-hack the kernel.