Re: Stop scheduler on panic

on 17/11/2011 18:37 John Baldwin said the following:
> On Thursday, November 17, 2011 4:47:42 am Andriy Gapon wrote:
>> on 17/11/2011 10:34 Andriy Gapon said the following:
>>> on 17/11/2011 10:15 Kostik Belousov said the following:
>>>> I have the following change for eons on my test boxes. Without it,
>>>> I simply cannot get _any_ dump.
>>>>
>>>> diff --git a/sys/cam/cam_xpt.c b/sys/cam/cam_xpt.c
>>>> index 10b89c7..a38e42f 100644
>>>> --- a/sys/cam/cam_xpt.c
>>>> +++ b/sys/cam/cam_xpt.c
>>>> _at__at_ -4230,7 +4230,7 _at__at_ xpt_done(union ccb *done_ccb)
>>>>  			TAILQ_INSERT_TAIL(&cam_simq, sim, links);
>>>>  			mtx_unlock(&cam_simq_lock);
>>>>  			sim->flags |= CAM_SIM_ON_DONEQ;
>>>> -			if (first)
>>>> +			if (first && panicstr == NULL)
>>>>  				swi_sched(cambio_ih, 0);
>>>>  		}
>>>>  	}
>>>
>>> I think that this (or similar) change should go into the patch and the tree.
>>>
>>
>> And, BTW, I still would like to do something like the following (perhaps with
>> td_oncpu = NOCPU and td_flags &= ~TDF_NEEDRESCHED also moved to the common code):
>>
>> Index: sys/kern/sched_ule.c
>> ===================================================================
>> --- sys/kern/sched_ule.c	(revision 227608)
>> +++ sys/kern/sched_ule.c	(working copy)
>> _at__at_ -1790,7 +1790,6 _at__at_ sched_switch(struct thread *td, struct thread *new
>>  	td->td_oncpu = NOCPU;
>>  	if (!(flags & SW_PREEMPT))
>>  		td->td_flags &= ~TDF_NEEDRESCHED;
>> -	td->td_owepreempt = 0;
>>  	tdq->tdq_switchcnt++;
>>  	/*
>>  	 * The lock pointer in an idle thread should never change.  Reset it
>> Index: sys/kern/kern_synch.c
>> ===================================================================
>> --- sys/kern/kern_synch.c	(revision 227608)
>> +++ sys/kern/kern_synch.c	(working copy)
>> _at__at_ -406,6 +406,8 _at__at_ mi_switch(int flags, struct thread *newtd)
>>  	    ("mi_switch: switch must be voluntary or involuntary"));
>>  	KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));
>>
>> +	td->td_owepreempt = 0;
>> +
>>  	/*
>>  	 * Don't perform context switches from the debugger.
>>  	 */
>> Index: sys/kern/sched_4bsd.c
>> ===================================================================
>> --- sys/kern/sched_4bsd.c	(revision 227608)
>> +++ sys/kern/sched_4bsd.c	(working copy)
>> _at__at_ -940,7 +940,6 _at__at_ sched_switch(struct thread *td, struct thread *new
>>  	td->td_lastcpu = td->td_oncpu;
>>  	if (!(flags & SW_PREEMPT))
>>  		td->td_flags &= ~TDF_NEEDRESCHED;
>> -	td->td_owepreempt = 0;
>>  	td->td_oncpu = NOCPU;
>>
>>  	/*
>>
>> Does anybody see any potential problems with such a change?
> 
> Hmm, does this mean the preemption will be lost if you break into the
> debugger and continue in the non-panic case?

Not sure which exact scenario you have in mind.
Please note that the above diff just moves resetting of td_owepreempt to an
earlier place.  As far as I can see there are no checks of td_owepreempt value
between the new place and the old places.

-- 
Andriy Gapon