Date: Tue, 28 Feb 2006 07:40:05 -0800 (PST)
From: Zwane Mwaikambo <zwane@arm.linux.org.uk>
To: Nathan Lynch <ntl@pobox.com>
cc: Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: i386 cpu hotplug bug - instant reboot when onlining secondary
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On Mon, 27 Feb 2006, Nathan Lynch wrote:

> Zwane Mwaikambo wrote:
> > On Sun, 19 Feb 2006, Nathan Lynch wrote:
> > 
> > > 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:
> > 
> > Does 2.6.14 work? Also i wonder if it gets out of the trampoline...
> 
> 2.6.14 works (albeit with an APIC error reported).  When retesting
> 2.6.16-rc4 with your patch on top of my debugging patch, I don't see the
> "startup_secondary" line:

Hi Nathan,

Can you try the following patch? We can start moving the WARM_BOOT_HLT 
down until it triple faults (i'm assuming it at least gets this far).

Index: linux-2.6.16-rc2-mm1/arch/i386/kernel/head.S
===================================================================
RCS file: /home/cvsroot/linux-2.6.16-rc2-mm1/arch/i386/kernel/head.S,v
retrieving revision 1.1.1.1
diff -u -p -B -r1.1.1.1 head.S
--- linux-2.6.16-rc2-mm1/arch/i386/kernel/head.S	11 Feb 2006 16:55:14 -0000	1.1.1.1
+++ linux-2.6.16-rc2-mm1/arch/i386/kernel/head.S	28 Feb 2006 15:34:34 -0000
@@ -146,6 +146,12 @@ page_pde_offset = (__PAGE_OFFSET >> 20);
  * we know the trampoline has already loaded the boot_gdt_table GDT
  * for us.
  */
+#define warm_boot	tsc_sync_disabled-__PAGE_OFFSET
+#define WARM_BOOT_HLT		\
+	cmpl	$0, warm_boot;	\
+10:				\
+	jne	10b
+
 ENTRY(startup_32_smp)
 	cld
 	movl $(__BOOT_DS),%eax
@@ -168,6 +174,8 @@ ENTRY(startup_32_smp)
  *	NOTE! We have to correct for the fact that we're
  *	not yet offset PAGE_OFFSET..
  */
+	WARM_BOOT_HLT
+
 #define cr4_bits mmu_cr4_features-__PAGE_OFFSET
 	movl cr4_bits,%edx
 	andl %edx,%edx
Index: linux-2.6.16-rc2-mm1/arch/i386/kernel/smpboot.c
===================================================================
RCS file: /home/cvsroot/linux-2.6.16-rc2-mm1/arch/i386/kernel/smpboot.c,v
retrieving revision 1.1.1.1
diff -u -p -B -r1.1.1.1 smpboot.c
--- linux-2.6.16-rc2-mm1/arch/i386/kernel/smpboot.c	11 Feb 2006 16:55:14 -0000	1.1.1.1
+++ linux-2.6.16-rc2-mm1/arch/i386/kernel/smpboot.c	28 Feb 2006 15:34:42 -0000
@@ -102,7 +102,7 @@ static cpumask_t smp_commenced_mask;
  * is no way to resync one AP against BP. TBD: for prescott and above, we
  * should use IA64's algorithm
  */
-static int __devinitdata tsc_sync_disabled;
+int __devinitdata tsc_sync_disabled;
 
 /* Per CPU bogomips and other parameters */
 struct cpuinfo_x86 cpu_data[NR_CPUS] __cacheline_aligned;

-
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