[PATCH] i386/x86-64: Don't IPI to offline cpus on shutdown

So why are we calling smp_send_stop from machine_halt?

We don't.

Looking more closely at the bug report the problem here
is that halt -p is called which triggers not a halt but
an attempt to power off.

machine_power_off calls machine_shutdown which calls smp_send_stop.

If pm_power_off is set we should never make it out machine_power_off
to the call of do_exit.  So pm_power_off must not be set in this case.
When pm_power_off is not set we expect machine_power_off to devolve
into machine_halt.

So how do we fix this?

Playing too much with smp_send_stop is dangerous because it
must also be safe to be called from panic.

It looks like the obviously correct fix is to only call
machine_shutdown when pm_power_off is defined.  Doing
that will make Andi's assumption about not scheduling
true and generally simplify what must be supported.

This turns machine_power_off into a noop like machine_halt
when pm_power_off is not defined.

If the expected behavior is that sys_reboot(LINUX_REBOOT_CMD_POWER_OFF)
becomes sys_reboot(LINUX_REBOOT_CMD_HALT) if pm_power_off is NULL
this is not quite a comprehensive fix as we pass a different parameter
to the reboot notifier and we set system_state to a different value
before calling device_shutdown().

Unfortunately any fix more comprehensive I can think of is not
obviously correct.  The core problem is that there is no architecture
independent way to detect if machine_power will become a noop, without
calling it.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/reboot.c

@@ -12,6 +12,7 @@
 #include <linux/efi.h>
 #include <linux/dmi.h>
 #include <linux/ctype.h>
+#include <linux/pm.h>
 #include <asm/uaccess.h>
 #include <asm/apic.h>
 #include <asm/desc.h>
@@ -355,10 +356,10 @@ void machine_halt(void)
 
 void machine_power_off(void)
 {
+	if (pm_power_off) {
 		machine_shutdown();
-
-	if (pm_power_off)
 		pm_power_off();
+	}
 }
 
 

arch/x86_64/kernel/reboot.c

@@ -6,6 +6,7 @@
 #include <linux/kernel.h>
 #include <linux/ctype.h>
 #include <linux/string.h>
+#include <linux/pm.h>
 #include <asm/io.h>
 #include <asm/kdebug.h>
 #include <asm/delay.h>
@@ -154,10 +155,11 @@ void machine_halt(void)
 
 void machine_power_off(void)
 {
+	if (pm_power_off) {
 		if (!reboot_force) {
 			machine_shutdown();
 		}
-	if (pm_power_off)
 		pm_power_off();
+	}
 }