Re: Consistent kernel hang during heavy TCP connection handling load

[Bill Davidsen <davidsen@tmr.com>]

Andrew A. wrote:
> Jan,
> 
> Thanks for responding.  When I got no responses, I searched for ways to get more data out of the kernel--I must say that it has been
> quite a journey to identify what is working, where to get it, and how to install it when it comes to kernel
> debugging/crash-data-gathering tools.  LKCD for example, is not available at the location you'll eventually arrive at if you search
> for it in google ... it's not obvious what it's state is (current/defunct/superceded), there's KDB, KGDB, netdump, netconsol,
> netlog, diskdump (conusingly known as lkdump) etc. etc.  And then, even if you do figure out what tools are current, you then have
> to match the tool to the particular kernel version you are running -- which can be a task and a half unto itself.
> 
> Is diskdump available for 2.4?  Can anyone comment on the choice of tools below?
> 
> Anyway, I have also done all of the following:
> 
> (1) Enabled netdump/netconsole on 2.6.8.1-521 Fedora Core kernel, after first fixing the startup scripts.  Fixes can be found at
> www.memeplex.com/Linux.html  Note that after I also fixed crash.c to be a 2.6 compliant kernel module, and loading it to test
> netdump, I always end up with a vmcore-incomplete image approx 45k in size, on the netdump-server.  Can anyone tell me if this is
> absurdly small, and if so, what might be the solution?  The client box always reboots so I suspect too-small timeouts are the issue.

My experience is 100% with RH kernels, but the dump should be about 
memory size, in my case 2.5G or 4G and it is. But I did see hangs which 
resulted in the size you mention, a few k and hang.

There was a patch floating around to write a core image to a disk 
partition like Solaris, AIX, and other commercial systems, but Linus was 
opposed for some reason I remember as "I don't need this and it culd be 
dangerous" or similar. If that can be retrofitted to a current kernel it 
would be more useful than netdump, I suspect.

In any case, the short answer is that what you see is way too short, it 
sounds like the header info on config, registers, or somesuch that 
netdump sends first before the core.

-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me