dc TX underrun leads to delayed crash

[Mike Silbersack]

On Wed, 30 Jul 2003, Peter C. Lai wrote:

> I'm noticing on a moderately loaded system, that sometimes when the kernel
> increases the TX threshold (/kernel: dc0: TX underrun -- increasing TX
> threshold), a few minutes later, the system hardlocks requiring a reset.
> This routinely happens when I'm streaming MP3s over the network and the box
> suddenly hardlocks; after I go back to inspect the logs, the TX buffer underrun
> is the only thing in the log before the start of the kernel reboot messages.
> This is occuring on 4.8-STABLE as of July 7, 2003 on an AMD K6-2 500 with
> 348 Mb RAM and VIA Apollo MVP3 chipset. When the lockups occur, the system
> temperatures are below 40C, with little disk activity, moderate ram and cpu
> usage; the NIC (linksys LNE-100TX A) is usually doing a steady 50K/s at this point.
> --
> Peter C. Lai

Rev 1.9.2.47 of if_dc.c (committed July 14th) should fix this problem for
you.  MBUF_STRESS_TEST showed similar symptoms as mbuf chain lengths were
increased, which is how I detected the problem.

Try grabbing the new if_dc.c:

http://www.freebsd.org/cgi/cvsweb.cgi/~checkout~/src/sys/pci/if_dc.c?rev=1.9.2.47&content-type=text/plain

And see how things go.

Mike "Silby" Silbersack