stable/11 debugging kernel unable to produce crashdump again

[Eugene Grosbein]

On 24.07.2017 08:44, Mark Johnston wrote:

>> Sadly, this time 11.1-STABLE r321371 SMP hangs instead of doing crashdump:
> 
> Is this amd64 GENERIC, or something else?

Custom kernel, amd64.

> 
>>
>> - "call doadump" from DDB prompt works just fine;
>> - "shutdown -r now" reboots the system without problems;
>> - "sysctl debug.kdb.panic=1" triggers a panic just fine but system hangs just afer showing uptime
>> instead of continuing with crashdump generation; same if "real" panic occurs.
>>
>> Same for debug.minidump set to 1 or 0. How do I debug this?
> 
> I'm not able to reproduce the problem in bhyve using r321401. Looking
> at the code, the culprits might be cngrab(), or one of the
> shutdown_post_sync eventhandlers. Since you're apparently able to see
> the console output at the time of the panic, I guess it's probably the
> latter. Could you try your test with the patch below applied? It'll
> print a bunch of "entering post_sync"/"leaving post_sync" messages with
> addresses that can be resolved using kgdb. That'll help determine where
> we're getting stuck.
> 
> Index: sys/sys/eventhandler.h
> ===================================================================
> --- sys/sys/eventhandler.h	(revision 321401)
> +++ sys/sys/eventhandler.h	(working copy)
> @@ -85,7 +85,11 @@
>  			_t = (struct eventhandler_entry_ ## name *)_ep;	\
>  			CTR1(KTR_EVH, "eventhandler_invoke: executing %p", \
>   			    (void *)_t->eh_func);			\
> +			if (strcmp(__STRING(name), "shutdown_post_sync") == 0) \
> +				printf("entering post_sync %p\n", (void *)_t->eh_func); \
>  			_t->eh_func(_ep->ee_arg , ## __VA_ARGS__);	\
> +			if (strcmp(__STRING(name), "shutdown_post_sync") == 0) \
> +				printf("leaving post_sync %p\n", (void *)_t->eh_func); \
>  			EHL_LOCK((list));				\
>  		}							\
>  	}								\
> 

I'l try this evening.