Date: Thu, 01 Dec 2011 23:42:20 +0200 From: Andriy Gapon <avg@FreeBSD.org> To: John Baldwin <jhb@FreeBSD.org> Cc: freebsd-current@FreeBSD.org Subject: Re: Stop scheduler on panic Message-ID: <4ED7F4BC.3080206@FreeBSD.org> In-Reply-To: <201112011553.34432.jhb@freebsd.org> References: <20111113083215.GV50300@deviant.kiev.zoral.com.ua> <201112011349.50502.jhb@freebsd.org> <4ED7E6B0.30400@FreeBSD.org> <201112011553.34432.jhb@freebsd.org>
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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@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
>> @@ -200,7 +200,7 @@ 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:
@@ -428,6 +428,8 @@ 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
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