I was having a problem with the NMI testing hanging on an SMP system
in check_nmi_watchdog() when using nmi_watchdog=2. It doesn't seem to
happen on a stock kernel, but I was working on something else and it
triggered this problem.
This patch solves the problem. I'm not sure this is quite the right
solution, but I know that the local_irq_enable() is kind of pointless
here and it seems that having scheduling on while the other CPUs are
locked up with interrupts off is a bad idea. And you can't call
smp_call_function() with interrupts off. But adding the preempt
disable around this operation seems to solve the problem.
Signed-off-by: Corey Minyard <[email protected]>
Index: linux-2.6.18/arch/i386/kernel/nmi.c
===================================================================
--- linux-2.6.18.orig/arch/i386/kernel/nmi.c
+++ linux-2.6.18/arch/i386/kernel/nmi.c
@@ -134,12 +134,18 @@ static int __init check_nmi_watchdog(voi
printk(KERN_INFO "Testing NMI watchdog ... ");
+ /*
+ * We must have preempt off while testing the local APIC
+ * watchdog. If we have an interrupt on this CPU while the
+ * other CPUs are wedged, and that interrupt tries to schedule
+ * (and possibly do an IPC), we would be hung.
+ */
+ preempt_disable();
if (nmi_watchdog == NMI_LOCAL_APIC)
smp_call_function(nmi_cpu_busy, (void *)&endflag, 0, 0);
for_each_possible_cpu(cpu)
prev_nmi_count[cpu] = per_cpu(irq_stat, cpu).__nmi_count;
- local_irq_enable();
mdelay((10*1000)/nmi_hz); // wait 10 ticks
for_each_possible_cpu(cpu) {
@@ -151,6 +157,7 @@ static int __init check_nmi_watchdog(voi
#endif
if (nmi_count(cpu) - prev_nmi_count[cpu] <= 5) {
endflag = 1;
+ preempt_enable();
printk("CPU#%d: NMI appears to be stuck (%d->%d)!\n",
cpu,
prev_nmi_count[cpu],
@@ -162,6 +169,7 @@ static int __init check_nmi_watchdog(voi
}
}
endflag = 1;
+ preempt_enable();
printk("OK.\n");
/* now that we know it works we can reduce NMI frequency to
-
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