linux-kernel - Is register_cpu() now obligatory?

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Message-ID: <4F0A3C3B.5090700@nod.at>
Date:	Mon, 09 Jan 2012 02:00:43 +0100
From:	Richard Weinberger <richard@....at>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	gregkh@...e.de,
	"user-mode-linux-devel@...ts.sourceforge.net" 
	<user-mode-linux-devel@...ts.sourceforge.net>
Subject: Is register_cpu() now obligatory?

Hi!

In Linus' tree as of today UML is broken.
It's crashing because get_cpu_device() in topology_add_dev()
returns a device with an invalid kobj (address is 0x10).

The code seems to assume that each arch has to register their CPUs
using register_cpu().

Is this a regression or was UML always faulty because it did not register it's CPU?

The below patch fixes the issue for UML.

Thanks,
//richard

---
diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile
index bc49474..f3b43fe 100644
--- a/arch/um/kernel/Makefile
+++ b/arch/um/kernel/Makefile
@@ -12,7 +12,7 @@ clean-files :=
 obj-y = config.o exec.o exitcode.o init_task.o irq.o ksyms.o mem.o \
 	physmem.o process.o ptrace.o reboot.o sigio.o \
 	signal.o smp.o syscall.o sysrq.o time.o tlb.o trap.o \
-	um_arch.o umid.o skas/
+	um_arch.o umid.o cpu.o skas/

 obj-$(CONFIG_BLK_DEV_INITRD) += initrd.o
 obj-$(CONFIG_GPROF)	+= gprof_syms.o
diff --git a/arch/um/kernel/cpu.c b/arch/um/kernel/cpu.c
new file mode 100644
index 0000000..4914df2
--- /dev/null
+++ b/arch/um/kernel/cpu.c
@@ -0,0 +1,19 @@
+#include <linux/init.h>
+#include <linux/device.h>
+#include <linux/cpu.h>
+#include <linux/percpu.h>
+
+static DEFINE_PER_CPU(struct cpu, cpu_devices);
+
+static int __init topology_init(void)
+{
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		struct cpu *c = &per_cpu(cpu_devices, cpu);
+		register_cpu(c, cpu);
+	}
+
+	return 0;
+}
+subsys_initcall(topology_init);


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