Re: [patch] Re: 2.6.16-rc4-mm1 (bugs and lockups)

[Stas Sergeev]

Hello.

Andrew Morton wrote:
> umm, actually it's wrong.  i386's smp_prepare_boot_cpu() diddles with
> per-cpu memory, and that's not initialised at that stage.  See the call to
> setup_per_cpu_areas() a few lines later.
> So I'll drop that hunk.  How important is it in practice?
It was important because it used to fix both the printk and
(completely accidentally!) the boot problem itself.

> #ifdef CONFIG_SMP
> 	cpu_set(smp_processor_id(), cpu_online_map);	/* comment */
> #endif
I don't even think #ifdef is needed. Having that for the UP
case may be useless, yet looks consistent to me.

> right there in start_kernel()?
This is enough for printk but not for the boot lockup.
The attached patch is however enough. And it should be
correct, as it is consistent with an UP case.

> (That assumes that smp_processor_id() works at that stage.  Surely that's
> true).
Looking into the arch-specific code, I can see that some
arches evaluate the boot-cpu number by some other means,
not by the smp_processor_id(). Still I am pretty sure the
patch won't hurt them.

With this patch and with the hotfixes, I've got the -mm
kernel working, thanks.

----

Register the boot-cpu in the cpu maps earlier to allow the
early printk to work, and to fix an obscure deadlock at boot.

Signed-off-by: Stas Sergeev <stsp@xxxxxxxx>

--- a/init/main.c	2006-02-21 10:36:04.000000000 +0300
+++ b/init/main.c	2006-02-22 11:30:01.000000000 +0300
@@ -440,6 +440,15 @@
  *	Activate the first processor.
  */
 
+static void boot_cpu_init(void)
+{
+	int cpu = smp_processor_id();
+	/* Mark the boot cpu "present", "online" etc for SMP and UP case */
+	cpu_set(cpu, cpu_online_map);
+	cpu_set(cpu, cpu_present_map);
+	cpu_set(cpu, cpu_possible_map);
+}
+
 asmlinkage void __init start_kernel(void)
 {
 	char * command_line;
@@ -449,17 +458,13 @@
  * enable them
  */
 	lock_kernel();
+	boot_cpu_init();
 	page_address_init();
 	printk(KERN_NOTICE);
 	printk(linux_banner);
 	setup_arch(&command_line);
 	setup_per_cpu_areas();
-
-	/*
-	 * Mark the boot cpu "online" so that it can call console drivers in
-	 * printk() and can access its per-cpu storage.
-	 */
-	smp_prepare_boot_cpu();
+	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
 
 	/*
 	 * Set up the scheduler prior starting any interrupts (such as the