Bug#513537: linux-image-2.6.26-1-openvz-amd64 hanging

[Vitaliy Gusev <vgusev@openvz.org>]

Hi, Tom.

On Tuesday 31 March 2009 12:26:54 am Tom Rathborne wrote:
> Hi Vitaliy,
>
> I have attached another set of debug info from another case of this bug.
> I was away last week so didn't notice it until today.
>
> The files are split up better so it should be easier to read.
>
> One small problem: sysrq-t filled the kernel ring buffer, so you don't
> get the whole dump.
>
> One big problem: sysrq-d said:
>     [913235.239639] Show Locks Held
>     [913235.239639] INFO: lockdep is turned off.
>
> But my kernel config reads:
>     CONFIG_LOCKDEP_SUPPORT=y
>     CONFIG_LOCKDEP=y
>     CONFIG_DEBUG_LOCKDEP=y
>
> How do I turn on lockdep debugging? I see there are system calls
> lockdep_on()/lockdep_off(), so I wrote a C program which calls
> lockdep_on(), which ran fine, but I still get:
>     INFO: lockdep is turned off.
> Please tell me what to do to turn lockdep debugging on!

1. It occured because lockdep warning was emitted :
         Mar 23 11:54:58 magrathea kernel: [260871.208985] [ INFO: hard-safe -> hard-unsafe lock order detected ]
         Mar 23 11:54:58 magrathea kernel: [260871.209050] 2.6.26-tp5-openvz #1
         ...

Lockdep switches off lockdep by calling  debug_locks_off()  if some warnings occur or tained module was loaded.
debug_locks_off() sets debug_locks to zero. lockdep_on() doesn't set debug_locks.


2. We need sysrq-D info after lockup, so try to compile kernel without CONFIG_BEANCOUNTERS.

>