Re: Stop scheduler on panic

on 01/12/2011 22:53 John Baldwin said the following:
> On Thursday, December 01, 2011 3:42:24 pm Andriy Gapon wrote:
>> Returning to critical_exit, what do you think about the following patch?
>> I guess that it could be committed independently of / before the
>> SCHEDULER_STOPPED thing.
>>
>> commit ee3d1a04985e86911a68d854439ae8c5429b7bd5
>> Author: Andriy Gapon <avg_at_icyb.net.ua>
>> Date:   Thu Dec 1 18:53:36 2011 +0200
>>
>>     critical_exit: ignore td_owepreempt if kdb_active
>>
>>     calling mi_switch in such a context result in a recursion via
>>     kdb_switch
>>
>> diff --git a/sys/kern/kern_switch.c b/sys/kern/kern_switch.c
>> index 93cbf7b..885dc22 100644
>> --- a/sys/kern/kern_switch.c
>> +++ b/sys/kern/kern_switch.c
>> _at__at_ -200,7 +200,7 _at__at_ critical_exit(void)
>>
>>  	if (td->td_critnest == 1) {
>>  		td->td_critnest = 0;
>> -		if (td->td_owepreempt) {
>> +		if (td->td_owepreempt && !kdb_active) {
>>  			td->td_critnest = 1;
>>  			thread_lock(td);
>>  			td->td_critnest--;
> 
> I think this is fine, but I'd probably change this to SCHEDULER_STOPPED()
> in the SCHEDULER_STOPPED() patch.

I don't understand why...  What if kdb is entered for some other reason, not
because of panic?  In that case SCHEDULER_STOPPED() would be false, but it is
still possible to find a way into mi_switch.

The SCHEDULER_STOPPED patch adds this:
_at__at_ -428,6 +428,8 _at__at_ mi_switch(int flags, struct thread *newtd)
         */
        if (kdb_active)
                kdb_switch();
+       if (SCHEDULER_STOPPED())
+               return;
        if (flags & SW_VOL) {
                td->td_ru.ru_nvcsw++;
                td->td_swvoltick = ticks;
-- 
Andriy Gapon