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

On Thu, 2011-07-21 at 16:32 +0200, Francois Romieu wrote:

Richard Kennedy [off-list ref] :

quoted

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.

quoted

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 ?

quoted

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

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

quoted

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 ?

Thanks Francois,
I'll try the reboot= tomorrow.

I don't really know when my last know good was, it could be that
via-velocity change, but the problem is so intermittent it's difficult
to be sure. I've been trying to stress the network to make the problem
happen sooner but I've had no luck yet.

regards
Richard