netdev - Re: [Bug 10238] Re: [PATCH] Re: netconsole still hangs

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Date:	Tue, 18 Mar 2008 14:47:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	davem@...emloft.net, shemminger@...ux-foundation.org,
	netdev@...r.kernel.org, rjw@...k.pl,
	bugme-daemon@...zilla.kernel.org
Subject: Re: [Bug 10238] Re: [PATCH] Re: netconsole still hangs

On Tue, 18 Mar 2008 22:05:42 +0100
Jarek Poplawski <jarkao2@...il.com> wrote:

> Andrew Morton wrote, On 03/18/2008 09:50 AM:
> ...
> > As a last resort.  But it'd surely be better if a net developer could
> > reproduce this and do some work on it.  It's bog-trivial to reproduce here
> > and afaik nobody has even tried.  Perhaps you have...
> > 
> > service syslog stop
> > while true
> > do
> > 	echo t > /proc/sysrq-trigger
> > done
> > 
> > and that's it.
> 
> Alas my testing possibilities, especially with real network, are very
> limited, I can confirm: yes, the above test really hangs my box, yet
> with syslog on and netconsole off. So, maybe I miss something, but I
> don't understand why do you expect netconsole should endure this?

I expect it to fail coz it's recently been filled with bugs ;)

I see that your netpoll-zap_completion_queue-adjust-skb-users-counter.patch
should fix the oops I earlier hit.  Good.

> IMHO, after the below patch to sched.c you can't compare netconsole to
> 2.6.24 with this sysrq-trigger test; any bugs found with this could be
> something old and not necessarily in netconsole (could be only exposed
> by netconsole like this earlier mentioned, unexplained, probably after
> double kfree OOPS).
> 
> Regards,
> Jarek P.
> 
> From: Nick Piggin <nickpiggin@...oo.com.au>
> Date: Fri, 25 Jan 2008 20:08:34 +0000 (+0100)
> Subject: sched: print backtrace of running tasks too
> X-Git-Tag: v2.6.25-rc1~1237^2~3
> X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=5fb5e6de55860a99c2d8fe7e0c8222d5c53d8464
> 
> sched: print backtrace of running tasks too
> 
> The attached patch is something really simple that can sometimes help
> in getting more info out of a hung system.
> 
> Signed-off-by: Ingo Molnar <mingo@...e.hu>
> ---
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 4d3a5a7..524285e 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -5161,8 +5161,7 @@ void sched_show_task(struct task_struct *p)
>  	printk(KERN_CONT "%5lu %5d %6d\n", free,
>  		task_pid_nr(p), task_pid_nr(p->real_parent));
>  
> -	if (state != TASK_RUNNING)
> -		show_stack(p, NULL);
> +	show_stack(p, NULL);
>  }
>  
>  void show_state_filter(unsigned long state_filter)

hm.

I tried a few things:

1:

   cat monstrous-text-file > /dev/kmsg

  Works OK.

2:

   Disable netconsole, do

	while true
	do
		echo t > /proc/sysrq-trigger
	done

   Works OK.

3:

  Enable netconsole, do

	while true
	do
		echo t > /proc/sysrq-trigger
	done

  Output comes out.  I was able to ^C the while loop.  After a while the
  output stopped.  So that seems OK too.


So right now it's cannot-reproduce.  I'll try things on the other machine
this evening.

I dunno why the sched.c change causes your sysrq-T operation to fail.  Can
you provide more details please?


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