[poll / rfc] kdb_stop_cpus

[Andriy Gapon]

on 03/06/2011 20:57 Robert N. M. Watson said the following:
> 
> On 3 Jun 2011, at 16:13, Andriy Gapon wrote:
> 
>> I wonder if anybody uses kdb_stop_cpus with non-default value. If, yes, I
>> am very interested to learn about your usecase for it.
> 
> The issue that prompted the sysctl was non-NMI IPIs being used to enter the
> debugger or reboot following a core hanging with interrupts disabled. With
> the switch to NMI IPIs in some of those circumstances, life is better -- at
> least, on hardware that supports non-maskable IPIs. I seem to recall sparc64
> doesn't, however?

Seems to be so as Nathan has also pointed out for PPC.
For this I also plan the following change:

commit 458ebd9aca7e91fc6e0825c727c7220ab9f61016

    generic_stop_cpus: move timeout detection code from under DIAGNOSTIC

    ... and also increase it a bit.
    IMO it's better to detect and report the (rather serious) condition and
    allow a system to proceed somehow rather than be stuck in an endless
    loop.

diff --git a/sys/kern/subr_smp.c b/sys/kern/subr_smp.c
index ae52f4b..4bd766b 100644
--- a/sys/kern/subr_smp.c
+++ b/sys/kern/subr_smp.c
@@ -232,12 +232,10 @@ generic_stop_cpus(cpumask_t map, u_int type)
 		/* spin */
 		cpu_spinwait();
 		i++;
-#ifdef DIAGNOSTIC
-		if (i == 100000) {
+		if (i == 100000000) {
 			printf("timeout stopping cpus\n");
 			break;
 		}
-#endif
 	}

 	stopping_cpu = NOCPU;


> Not sure about MIPS, etc. Attilio has since significantly
> improved our shutdown behaviour -- initially, the switch to NMI IPIs broke
> other things (because certain IPIs then improperly preempted threads holding
> spinlocks), but that pretty much all seems worked out now.

-- 
Andriy Gapon