linux-kernel - Re: Problems with -git14

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Date:	Wed, 30 Apr 2008 16:17:46 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	"J.A. Magallón" <jamagallon@....com>
cc:	Glauber Costa <gcosta@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: Problems with -git14

On Wed, 30 Apr 2008, J.A. Magallón wrote:
> 
> I have a couple problems with latest git (-14):
> 
> - It only recognises 2 processors out of 4 (dual Xeon HT)
> - It oopses on the swapper process just on boot...
> 
> Difference in dmesg is below. If full correct dmesg or config is
> needed, please ask for them. The kernel was built copying old
> 2.6.25 config to .config && make oldconfig. I filled the missing
> gaps like PAT and others...
> 
> -Brought up 4 CPUs
> +native_cpu_up: bad cpu 2
> +native_cpu_up: bad cpu 3
> +Brought up 2 CPUs

Yes, I've been getting this for some days too: only 2 processors on
dual Xeon HT in 32-bit mode; whereas x86_64 finds all 4 just fine.
Ran lots of testing on 2.6.25-mm1 before I noticed it there.

I bisected for a while, but it got confusing (arrived at a bisect
point which gave only 1 processor: smpboot code getting rearranged),
so I was forced (quel horreur!) to investigate properly.  I've just
now had success with the patch below, please give it a try:
but it'll need an Ack from Glauber before it can go in.

> +WARNING: at include/linux/blkdev.h:427 blk_queue_init_tags+0x110/0x11f()

I presume this warning and backtrace is what you report as an oops:
I think you'll find Linus included a fix for this one overnight, and
it should have gone away in 2.6.25-git15 (but I didn't see it myself).

Hugh

[PATCH] x86_32: fix HT cpu booting

Since recent smpboot 32/64-bit merge, my dual Xeon with HT has been
booting only 2 of its 4 cpus (when running an i386 kernel; but x86_64
is okay).  J.A. Magallón reports the same.

native_cpu_up: bad cpu 2
native_cpu_up: bad cpu 3

The mach-default cpu_present_to_apicid() was just returning cpu number
(2, 3) instead of apicid (6, 7): looks like we now need the x86_64 code
even for the i386 case.

Comparing with other versions of cpu_present_to_apicid(), it seems a
good idea to include an NR_CPUS test too, since cpu_present() doesn't
include that; but that wasn't a problem here, and may no problem at all.

One point worth noting - is it a worry?  Prior to that smpboot merge,
my Xeon booted the two HT siblings on one physical first, then the
two siblings on the other physical after - when i386, but alternated
them when x86_64.  Since the merge, the x86_64 sequence is unchanged,
but the i386 sequence is now like x86_64.  I prefer this consistency,
and I prefer the new sequence: booting with maxcpus=2 then uses the
independent physicals without HT sharing; but surprises in store?

Signed-off-by: Hugh Dickins <hugh@...itas.com>

--- 2.6.25-git/include/asm-x86/mach-default/mach_apic.h	2008-04-23 07:24:16.000000000 +0100
+++ linux/include/asm-x86/mach-default/mach_apic.h	2008-04-30 14:55:14.000000000 +0100
@@ -109,13 +109,8 @@ static inline int cpu_to_logical_apicid(

 static inline int cpu_present_to_apicid(int mps_cpu)
 {
-#ifdef CONFIG_X86_64
-	if (cpu_present(mps_cpu))
+	if (mps_cpu < NR_CPUS && cpu_present(mps_cpu))
 		return (int)per_cpu(x86_bios_cpu_apicid, mps_cpu);
-#else
-	if (mps_cpu < get_physical_broadcast())
-		return  mps_cpu;
-#endif
 	else
 		return BAD_APICID;
 }