Author: avg
Date: Sun Nov 25 14:22:08 2012
New Revision: 243515
URL: http://svnweb.freebsd.org/changeset/base/243515
Log:
remove stop_scheduler_on_panic knob
There has not been any complaints about the default behavior, so there
is no need to keep a knob that enables the worse alternative.
Now that the hard-stopping of other CPUs is the only behavior, the panic_cpu
spinlock-like logic can be dropped, because only a single CPU is
supposed to win stop_cpus_hard(other_cpus) race and proceed past that
call.
MFC after: 1 month
Modified:
head/sys/kern/kern_shutdown.c
Modified: head/sys/kern/kern_shutdown.c
==============================================================================
--- head/sys/kern/kern_shutdown.c Sun Nov 25 12:38:12 2012
(r243514)
+++ head/sys/kern/kern_shutdown.c Sun Nov 25 14:22:08 2012
(r243515)
@@ -121,11 +121,6 @@ SYSCTL_INT(_kern, OID_AUTO, sync_on_pani
&sync_on_panic, 0, "Do a sync before rebooting from a panic");
TUNABLE_INT("kern.sync_on_panic", &sync_on_panic);
-static int stop_scheduler_on_panic = 1;
-SYSCTL_INT(_kern, OID_AUTO, stop_scheduler_on_panic, CTLFLAG_RW | CTLFLAG_TUN,
- &stop_scheduler_on_panic, 0, "stop scheduler upon entering panic");
-TUNABLE_INT("kern.stop_scheduler_on_panic", &stop_scheduler_on_panic);
-
static SYSCTL_NODE(_kern, OID_AUTO, shutdown, CTLFLAG_RW, 0,
"Shutdown environment");
@@ -552,7 +547,6 @@ void
panic(const char *fmt, ...)
{
#ifdef SMP
- static volatile u_int panic_cpu = NOCPU;
cpuset_t other_cpus;
#endif
struct thread *td = curthread;
@@ -560,39 +554,27 @@ panic(const char *fmt, ...)
va_list ap;
static char buf[256];
- if (stop_scheduler_on_panic)
- spinlock_enter();
- else
- critical_enter();
+ spinlock_enter();
#ifdef SMP
/*
- * We don't want multiple CPU's to panic at the same time, so we
- * use panic_cpu as a simple spinlock. We have to keep checking
- * panic_cpu if we are spinning in case the panic on the first
- * CPU is canceled.
+ * stop_cpus_hard(other_cpus) should prevent multiple CPUs from
+ * concurrently entering panic. Only the winner will proceed
+ * further.
*/
- if (panic_cpu != PCPU_GET(cpuid))
- while (atomic_cmpset_int(&panic_cpu, NOCPU,
- PCPU_GET(cpuid)) == 0)
- while (panic_cpu != NOCPU)
- ; /* nothing */
-
- if (stop_scheduler_on_panic) {
- if (panicstr == NULL && !kdb_active) {
- other_cpus = all_cpus;
- CPU_CLR(PCPU_GET(cpuid), &other_cpus);
- stop_cpus_hard(other_cpus);
- }
-
- /*
- * We set stop_scheduler here and not in the block above,
- * because we want to ensure that if panic has been called and
- * stop_scheduler_on_panic is true, then stop_scheduler will
- * always be set. Even if panic has been entered from kdb.
- */
- td->td_stopsched = 1;
+ if (panicstr == NULL && !kdb_active) {
+ other_cpus = all_cpus;
+ CPU_CLR(PCPU_GET(cpuid), &other_cpus);
+ stop_cpus_hard(other_cpus);
}
+
+ /*
+ * We set stop_scheduler here and not in the block above,
+ * because we want to ensure that if panic has been called and
+ * stop_scheduler_on_panic is true, then stop_scheduler will
+ * always be set. Even if panic has been entered from kdb.
+ */
+ td->td_stopsched = 1;
#endif
bootopt = RB_AUTOBOOT;
@@ -632,8 +614,6 @@ panic(const char *fmt, ...)
/* thread_unlock(td); */
if (!sync_on_panic)
bootopt |= RB_NOSYNC;
- if (!stop_scheduler_on_panic)
- critical_exit();
kern_reboot(bootopt);
}
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