linux-kernel - Re: [patch] x86: 2.6.31-rc7 crash due to buggy flat_phys_pkg

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Date:	Tue, 25 Aug 2009 12:20:55 -0700
From:	Ravikiran G Thirumalai <kiran@...lex86.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Yinghai Lu <yinghai@...nel.org>,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	shai@...lex86.org, Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [patch] x86: 2.6.31-rc7 crash due to buggy flat_phys_pkg_id

On Tue, Aug 25, 2009 at 10:31:30PM +0400, Cyrill Gorcunov wrote:
>[Ingo Molnar - Tue, Aug 25, 2009 at 08:15:00PM +0200]
>| 
>
>I'm definitely not APIC expert but since I was partially involved
>letme turn in.
>
>Original commit which causes problem for vSMP seems to be due
>to cpu_has_apic bit turned off (ie due to being manually disabled
>or acpi table broken) so further read apic id will return plain
>zero (we're talking about 64 bits now). So frnakly I don't understand
>what is wrong with Ravikiran's patch. In case of apic disabled
>initial apic value will be used anyway (which is latched but
>actually may be changed, but it's not our case).
>

Exactly my thinking.  I hoped the patch I posted solves both cases --
does not depend on local apic id for the "fix crash on certain UP configs"
case in the commit here:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=2759c3287de27266e06f1f4e82cbd2d65f6a044c

And fixes vsmp too.

>Or perhaps there is an issue in srat numa nodes numbering?
>

Don't think so, local apic id has been used for for 'flat' and 'cluster'
apic (which was used prior to 'flat') for atleast 15 major releases.

Cyrill/Yinghai, can you test and confirm if the patch attached does not
regress the 'UP crash case' mentioned in
commit 2759c3287de27266e06f1f4e82cbd2d65f6a044c please?

---

2.6.31-rc7 does not boot on vSMPowered systems.  The sched domains
seem to build incorrectly with error messages of the sort:

[    8.501108] CPU31: Thermal monitoring enabled (TM1)
[    8.501127] CPU 31 MCA banks SHD:2 SHD:3 SHD:5 SHD:6 SHD:8
[    8.650254] CPU31: Intel(R) Xeon(R) CPU           E5540  @ 2.53GHz
stepping 04
[    8.710324] Brought up 32 CPUs
[    8.713916] Total of 32 processors activated (162314.96 BogoMIPS).
[    8.721489] ERROR: parent span is not a superset of domain->span
[    8.727686] ERROR: domain->groups does not contain CPU0
[    8.733091] ERROR: groups don't span domain->span
[    8.737975] ERROR: domain->cpu_power not set
[    8.742416]

This is followed by oopsen in the scheduler code
with NULL pointer deference in find_busiest_group.

Git bisection pointed to the following commit:

commit 2759c3287de27266e06f1f4e82cbd2d65f6a044c
x86: don't call read_apic_id if !cpu_has_apic

Upon examining the history of the commit, the above commit seems to be a fix
for:

commit 4797f6b021a3fa399942245d07a1feb30df81bb8
x86: read apic ID in the !acpi_lapic case

However, there appears to be bug in the commit
2759c3287de27266e06f1f4e82cbd2d65f6a044c, where flat_phys_pkg_id
uses initial apic id instead of hard_smp_processor_id() on SMP machines.
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=2759c3287de27266e06f1f4e82cbd2d65f6a044c

This patch fixes the bug and causes vSMPowered systems to boot up
correctly,

Signed-off-by: Ravikiran Thirumalai <kiran@...lex86.org>
Cc: Yinghai Lu <yinghai@...nel.org>

Index: linux-2.6.31-rc6/arch/x86/kernel/apic/apic_flat_64.c
===================================================================
--- linux-2.6.31-rc6.orig/arch/x86/kernel/apic/apic_flat_64.c	2009-08-21 12:42:16.000000000 -0700
+++ linux-2.6.31-rc6/arch/x86/kernel/apic/apic_flat_64.c	2009-08-21 14:12:21.654837472 -0700
@@ -161,7 +161,8 @@ static int flat_apic_id_registered(void)
 
 static int flat_phys_pkg_id(int initial_apic_id, int index_msb)
 {
-	return initial_apic_id >> index_msb;
+	return cpu_has_apic ? hard_smp_processor_id() >> index_msb :
+	    initial_apic_id >> index_msb;
 }
 
 struct apic apic_flat =  {


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