i386 cpu hotplug bug - instant reboot when onlining secondary

[Nathan Lynch <ntl@pobox.com>]

Hi-

On a dual P3 Xeon machine, offlining and then onlining a cpu makes the
box instantly reboot.  I've been seeing this throughout the 2.6.16-rc
series, but wasn't able to collect more information until now.  Not
sure when this last worked, unfortunately.

With the debugging patch below, I get this on serial console:

[17179681.704000] CPU 1 is now offline
[17179686.908000] Booting processor 1/1 eip 3000
[17179686.912000] CPU 1 irqstacks, hard=78383000 soft=7837b000
[17179686.920000] Setting warm reset code and vector.
[17179686.924000] 1.
[17179686.924000] 2.
[17179686.928000] 3.
[17179686.928000] Asserting INIT.
[17179686.932000] Waiting for send to finish...
[17179686.936000] +<7>Deasserting INIT.
[17179686.952000] Waiting for send to finish...
[17179686.956000] +<7>#startup loops: 2.
[17179686.960000] Sending STARTUP #1.
[17179686.960000] After apic_write.
[17179686.964000] Doing apic_write_around for target chip...
[17179686.972000] Doing apic_write_around to kick the second...

Any suggestions?


diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
index fb00ab7..85aff00 100644
--- a/arch/i386/kernel/smpboot.c
+++ b/arch/i386/kernel/smpboot.c
@@ -801,10 +801,12 @@ wakeup_secondary_cpu(int phys_apicid, un
 		 */
 
 		/* Target chip */
+		Dprintk("Doing apic_write_around for target chip...\n");
 		apic_write_around(APIC_ICR2, SET_APIC_DEST_FIELD(phys_apicid));
 
 		/* Boot on the stack */
 		/* Kick the second */
+		Dprintk("Doing apic_write_around to kick the second...\n");
 		apic_write_around(APIC_ICR, APIC_DM_STARTUP
 					| (start_eip >> 12));
 
diff --git a/include/asm-i386/apic.h b/include/asm-i386/apic.h
index d30b857..2c8dcfa 100644
--- a/include/asm-i386/apic.h
+++ b/include/asm-i386/apic.h
@@ -8,7 +8,7 @@
 #include <asm/processor.h>
 #include <asm/system.h>
 
-#define Dprintk(x...)
+#define Dprintk(fmt,arg...) printk(KERN_DEBUG fmt,##arg)
 
 /*
  * Debugging macros