[patch 3/9] cpu: deliver CPU_UP_CANCELED only to NOTIFY_OKed callbacks with CPU_UP_PREPARE

[Akinobu Mita]

From: Akinobu Mita <akinobu.mita@xxxxxxxxx>

The functions in a CPU notifier chain is called with CPU_UP_PREPARE event
before making the CPU online. If one of the callback returns NOTIFY_BAD,
it stops to deliver CPU_UP_PREPARE event, and CPU online operation is canceled.
Then CPU_UP_CANCELED event is delivered to the functions in a CPU notifier
chain again.

This CPU_UP_CANCELED event is delivered to the functions which have been
called with CPU_UP_PREPARE, not delivered to the functions which haven't
been called with CPU_UP_PREPARE.

The problem that makes existing cpu hotplug error handlings complex is
that the CPU_UP_CANCELED event is delivered to the function that has
returned NOTIFY_BAD, too.

Usually we don't expect to call destructor function against the
object that has failed to initialize. It is like:

	err = register_something();
	if (err) {
		unregister_something();
		return err;
	}

So it is natural to deliver CPU_UP_CANCELED event only to the functions
that have returned NOTIFY_OK with CPU_UP_PREPARE event and not to call
the function that have returned NOTIFY_BAD. This is what this patch is doing.

Otherwise, every cpu hotplug notifiler has to track whether
notifiler event is failed or not for each cpu.
(drivers/base/topology.c is doing this with topology_dev_map)

Similary this patch makes same thing with CPU_DOWN_PREPARE and
CPU_DOWN_FAILED evnets.

Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>

---
 kernel/cpu.c |    2 ++
 1 file changed, 2 insertions(+)

Index: 2.6-git/kernel/cpu.c
===================================================================
--- 2.6-git.orig/kernel/cpu.c
+++ 2.6-git/kernel/cpu.c
@@ -150,6 +150,7 @@ static int _cpu_down(unsigned int cpu, i
 	err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
 					hcpu, -1, &nr_calls);
 	if (err == NOTIFY_BAD) {
+		nr_calls--;
 		__raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 					  hcpu, nr_calls, NULL);
 		printk("%s: attempt to take down CPU %u failed\n",
@@ -233,6 +234,7 @@ static int __cpuinit _cpu_up(unsigned in
 	ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
 							-1, &nr_calls);
 	if (ret == NOTIFY_BAD) {
+		nr_calls--;
 		printk("%s: attempt to bring up CPU %u failed\n",
 				__FUNCTION__, cpu);
 		ret = -EINVAL;

-- 
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