linux-kernel - Re: [Qemu-ppc] [PATCH v2] powerpc/pseries: start rtasd before PCI probing

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Message-ID: <20160621110201.38d8711c@bahia.lan>
Date:	Tue, 21 Jun 2016 11:02:01 +0200
From:	Greg Kurz <groug@...d.org>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	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>,
	Thomas Huth <thuth@...hat.com>
Subject: Re: [Qemu-ppc] [PATCH v2] powerpc/pseries: start rtasd before PCI
 probing

On Wed, 15 Jun 2016 22:26:41 +0200
Greg Kurz <gkurz@...ux.vnet.ibm.com> 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>
> ---
> v2: - avoid behaviour change: don't create the proc entry if early init failed
> 

I forgot to mention that Thomas had sent a Tested-by for v1, which I think is
still valid for v2.

> Michael,
> 
> This was also tested under PowerVM: it doesn't fix anything there because the
> HMC tells it won't honor DLPAR features as long as the RMC isn't here, which
> happens later in the boot sequence. It hence seems impossible to have a pending
> RTAS event at boot time.
> 
> It doesn't seem to break anything either, the kernel boots and hotplug works
> okay once the RMC is up.
> 
> Cheers.
> 
> --
> Greg
> 
> ---
>  arch/powerpc/kernel/rtasd.c |   22 +++++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/rtasd.c b/arch/powerpc/kernel/rtasd.c
> index e864b7c5884e..a26a02006576 100644
> --- a/arch/powerpc/kernel/rtasd.c
> +++ b/arch/powerpc/kernel/rtasd.c
> @@ -526,10 +526,8 @@ void rtas_cancel_event_scan(void)
>  }
>  EXPORT_SYMBOL_GPL(rtas_cancel_event_scan);
>  
> -static int __init rtas_init(void)
> +static int __init rtas_event_scan_init(void)
>  {
> -	struct proc_dir_entry *entry;
> -
>  	if (!machine_is(pseries) && !machine_is(chrp))
>  		return 0;
>  
> @@ -562,13 +560,27 @@ static int __init rtas_init(void)
>  		return -ENOMEM;
>  	}
>  
> +	start_event_scan();
> +
> +	return 0;
> +}
> +arch_initcall(rtas_event_scan_init);
> +
> +static int __init rtas_init(void)
> +{
> +	struct proc_dir_entry *entry;
> +
> +	if (!machine_is(pseries) && !machine_is(chrp))
> +		return 0;
> +
> +	if (!rtas_log_buf)
> +		return -ENODEV;
> +
>  	entry = proc_create("powerpc/rtas/error_log", S_IRUSR, NULL,
>  			    &proc_rtas_log_operations);
>  	if (!entry)
>  		printk(KERN_ERR "Failed to create error_log proc entry\n");
>  
> -	start_event_scan();
> -
>  	return 0;
>  }
>  __initcall(rtas_init);
> 
>