linux-kernel - Re: powerpc/pseries: start rtasd before PCI probing

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Date:	Mon, 23 May 2016 20:39:02 +0200
From:	Greg Kurz <gkurz@...ux.vnet.ibm.com>
To:	Thomas Huth <thuth@...hat.com>
Cc:	Michael Ellerman <mpe@...erman.id.au>,
	Michael Roth <mdroth@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, qemu-ppc@...gnu.org,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>,
	kvm-ppc@...r.kernel.org
Subject: Re: powerpc/pseries: start rtasd before PCI probing

On Mon, 23 May 2016 20:23:19 +0200
Thomas Huth <thuth@...hat.com> wrote:

> On 23.05.2016 10:28, Greg Kurz wrote:
> > A strange behaviour is observed when comparing PCI hotplug in QEMU, between
> > x86 and pseries. If you consider the following steps:
> > - start a VM
> > - add a PCI device via the QEMU monitor before the rtasd has started (for
> >   example starting the VM in paused state, or hotplug during FW or boot
> >   loader)
> > - resume the VM execution
> > 
> > The x86 kernel detects the PCI device, but the pseries one does not.
> > 
> > This happens because the rtasd kernel worker is currently started under
> > device_initcall, while PCI probing happens earlier under subsys_initcall.
> > 
> > As a consequence, if we have a pending RTAS event at boot time, a message
> > is printed and the event is dropped.
> > 
> > This patch moves all the initialization of rtasd to arch_initcall, which is
> > run before subsys_call: this way, logging_enabled is true when the RTAS
> > event pops up and it is not lost anymore.
> > 
> > The proc fs bits stay at device_initcall because they cannot be run before
> > fs_initcall.
> > 
> > Signed-off-by: Greg Kurz <gkurz@...ux.vnet.ibm.com>
> > ---
> >  arch/powerpc/kernel/rtasd.c |   19 ++++++++++++++-----
> >  1 file changed, 14 insertions(+), 5 deletions(-)  
> 
> By the way, same is true for device UNplugging: When unplugging devices
> in QEMU while the firmware is still running, they are never properly
> removed from the guest. I've checked it, and your patch fixes this
> problem as well! Great :-)
> 
> Tested-by: Thomas Huth <thuth@...hat.com>
> 

Indeed, all pending RTAS events were lost... now rtasd will log them, up
to 64 events, but I did not test that far :)

Thanks for testing !

Cheers.

--
Greg