linux-kernel - Re: [LKML] Re: [LKML] [PATCH] Fix NULL pointer for Xen guests

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Date:	Tue, 4 May 2010 11:02:14 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	linux-kernel@...r.kernel.org, suresh.b.siddha@...el.com,
	x86@...nel.org, clalance@...hat.com, drjones@...hat.com
Subject: Re: [LKML] Re: [LKML] [PATCH] Fix NULL pointer for Xen guests

On Mon, May 03, 2010 at 03:16:34PM -0400, Konrad Rzeszutek Wilk wrote:
> >> OK, so your control domain is RHEL5. Mine is the Jeremy's xen/next one
> >> (2.6.32). Let me try to compile RHEL5 under FC11 - any tricks necessary
> >> to do that?
> >>    
> >
> > I haven't tried it -- it might work :)
> >
> > Also, did you try booting with maxvcpus > vcpus as drjones suggested ?
> 
> Yes. No luck reproducing the crash/panic. I am just not seeing the failure you
> guys are seeing.
> 
> Let me build once more 2.6.33 vanilla + CONFIG_DEBUG_MARK_RODATA=n) and check
> this. And also install a vanilla RHEL5 dom0 as it looks impossible to
> compile a 2.6.18-era kernel under FC11.

Rebuilding everything from scratch did it. I am seeing a similar
failure where xenctx reports:

Call Trace:
  [<ffffffff8107f780>] stop_cpu+0xc6  <--
  [<ffffffff8105520e>] worker_thread+0x15d 
  [<ffffffff8107f6ba>] __stop_machine+0x106 
  [<ffffffff81058afb>] wake_up_bit+0x25 
  [<ffffffff81038720>] spin_unlock_irqrestore+0x9 
  [<ffffffff810550b1>] spin_lock_irq+0xb 
  [<ffffffff810586cb>] kthread+0x7a 
  [<ffffffff8100a964>] kernel_thread_helper+0x4 
  [<ffffffff81009d61>] int_ret_from_sys_call+0x7 
  [<ffffffff814033dd>] retint_restore_args+0x5 
  [<ffffffff8100a960>] gs_change+0x13 

With this guest file:

kernel = "/mnt/lab/vs11/vmlinuz"
ramdisk = "/mnt/lab/vs11/initramfs.cpio.gz"
memory = 2048
maxvcpus = 4
vcpus = 2
vif = [ 'mac=00:0F:4B:00:00:71, bridge=switch' ]
vfb = [ 'vnc=1, vnclisten=0.0.0.0,vncunused=1']
root = "debug loglevel=10 plymouth:splash=solar plymouth:debug norm console=hvc0 initcall_debug"

This is with the latest linux kernel:
d93ac51c7a129db7a1431d859a3ef45a0b1f3fc5 (Merge branch 'for-linus' of
git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client)

With your patch the PV guests keeps on going.

So:

Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> 
> The Xen I am using is xen-unstable - so 4.0.1. I know that the IRQ balance
> code in the Xen hypervisor was fixed in 4.0 (it used to run out of
> context - now it runs in the IRQ context). Maybe this bug you are seeing
> (and have the fix for) is just a red-heering?

Interestingly enough, I couldn't reproduce this on my Intel box, but on
a AMD box with a very wacked TSC (cpu MHz         : 2795681.405) I can
reproduce this.

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