linux-kernel - Re: [PATCH] - Increase MAX_APICS for very large x86

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Date:	Thu, 19 Jun 2008 12:32:42 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jack Steiner <steiner@....com>
Cc:	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	Mike Travis <travis@....com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH] - Increase MAX_APICS for very large x86_64 configs


* Ingo Molnar <mingo@...e.hu> wrote:

> > The patch has no effect on any 32-bit kernel. It adds ~4k to the 
> > size of 64-bit kernels but only if NR_CPUS > 255.
> > 
> > This is a repost of an earlier patch (4/16) that was implicated in a 
> > random-qa failure. I have not been able to reproduce the failure 
> > using the same boot args & config.  Best guess is that some other 
> > patch caused random data corruption & this patch was a victim.
> 
> i have just re-tested the previously failing config on tip/master:
> 
>   http://redhat.com/~mingo/misc/config-Thu_Apr_17_10_17_14_CEST_2008.bad
>   http://people.redhat.com/mingo/tip.git/README
> 
> and the good news is that it does not crash on bootup anymore. Perhaps 
> one of Mike's fixes/improvements did the trick?

unfortunately it didnt last long, -tip randconfig auto-testing found 
that your patch causes a bootup crash:

[    0.352022] SMP mode deactivated.
[    0.355356] enabled ExtINT on CPU#0
[    0.358861] SMP disabled
[    0.361829] BUG: unable to handle kernel NULL pointer dereference at 00000000000008b0
[    0.364022] IP: [<ffffffff8028127b>] debug_mutex_add_waiter+0x4e/0x61
[    0.364022] PGD 0
[    0.364022] Thread overran stack, or stack corrupted

config, log and bzImage can be found here:

  http://redhat.com/~mingo/misc/config-Thu_Jun_19_12_10_40_CEST_2008.bad
  http://redhat.com/~mingo/misc/crash-Thu_Jun_19_12_10_40_CEST_2008.log
  http://redhat.com/~mingo/misc/bzImage-Thu_Jun_19_12_10_40_CEST_2008.bad

reverting your patch fixes the crash.

if you have trouble reproducing the problem then you should be able to 
stick the bzImage into any 64-bit PC's /etc/grub.conf (no initrd needed) 
and it should just crash straight away during bootup.

NOTE: -tip auto-testing randomizes various commonly used boot parameters 
as well, you can find them in the bootup log:

root=/dev/sda6 console=ttyS0,115200 earlyprintk=serial,ttyS0,115200 
debug initcall_debug apic=verbose sysrq_always_enabled ignore_loglevel 
selinux=0 maxcpus=1 nosmp no_hz=off highres=0 nmi_watchdog=0 noapic 
nolapic_timer hpet=disable idle=mwait idle=poll highmem=512m nopat notsc 
acpi=off pci=nomsi

this might be material to reproducing the crash.

NOTE2: the bzImage above will have the above boot parameters 
auto-appended, no need for you to configure them. But if you build your 
own kernel from tip/master using the above config you might have to add 
these boot parameters to the 'kernel' line of /etc/grub.conf to 
reproduce the crash.

	Ingo
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