1 files changed, 18 insertions, 4 deletions

diff --git a/arch/i386/kernel/irq.c b/arch/i386/kernel/irq.c
index 5785d84103a6..0f2ca590bf23 100644
--- a/arch/i386/kernel/irq.c
+++ b/arch/i386/kernel/irq.c
@@ -10,7 +10,6 @@
  * io_apic.c.)
  */
 
-#include <asm/uaccess.h>
 #include <linux/module.h>
 #include <linux/seq_file.h>
 #include <linux/interrupt.h>
@@ -21,19 +20,34 @@
 
 #include <asm/idle.h>
 
+#include <asm/apic.h>
+#include <asm/uaccess.h>
+
 DEFINE_PER_CPU(irq_cpustat_t, irq_stat) ____cacheline_internodealigned_in_smp;
 EXPORT_PER_CPU_SYMBOL(irq_stat);
 
-#ifndef CONFIG_X86_LOCAL_APIC
 /*
  * 'what should we do if we get a hw irq event on an illegal vector'.
  * each architecture has to answer this themselves.
  */
 void ack_bad_irq(unsigned int irq)
 {
-        printk("unexpected IRQ trap at vector %02x\n", irq);
-}
+        printk(KERN_ERR "unexpected IRQ trap at vector %02x\n", irq);
+
+#ifdef CONFIG_X86_LOCAL_APIC
+        /*
+         * Currently unexpected vectors happen only on SMP and APIC.
+         * We _must_ ack these because every local APIC has only N
+         * irq slots per priority level, and a 'hanging, unacked' IRQ
+         * holds up an irq slot - in excessive cases (when multiple
+         * unexpected vectors occur) that might lock up the APIC
+         * completely.
+         * But only ack when the APIC is enabled -AK
+         */
+        if (cpu_has_apic)
+                ack_APIC_irq();
 #endif
+}
 
 #ifdef CONFIG_4KSTACKS
 /*