Re: v3.0-rc* intermittent network failure: how to debug?

Richard Kennedy [off-list ref] :

I keep seeing a total network failure on v3.0.0-rc* , it is highly
intermittent, anything from 1 hour to 12+, and I don't have a reliable
test case.
When it fails I lose all network comms, but there are no errors in the
system log, no hung tasks reported, nothing. But after it fails the
machine hangs during shutdown, it just never turns off. So I guess
something is getting stuck but I can't find it.

Assuming the kernel hangs late enough, you can try the "reboot=" kernel
parameter and see if a value in arch/x86/include/asm/emergency-restart.h
makes a difference.

Can you suggest how to find out what going on? 

Switch into text mode before starting the reboot sequence then send a
magic sysrq T or W ?

I'm going to add a serial console and see if that helps.

It will help, especially with the kilometer long output of sysrq.

this is on a x86_64, via_velocity currently running 3.0.0-rc7 latest.

all suggestions gratefully received

Last via-velocity change in mainline dates back to may 25 (see
d10358de8d70aaeb965a974d56e9b72f6c6dbb3a). Were you previously fine
with a recent enough kernel to rule it out ?

-- 
Ueimor