linux-kernel - Re: PCI MSI breaks when booting with nosmp

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Message-Id: <200804231638.01479.jdelvare@suse.de>
Date:	Wed, 23 Apr 2008 16:38:01 +0200
From:	Jean Delvare <jdelvare@...e.de>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	linux-pci@...ey.karlin.mff.cuni.cz,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	Tejun Heo <htejun@...il.com>,
	Tom Long Nguyen <tom.l.nguyen@...el.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Jeff Garzik <jgarzik@...ox.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: PCI MSI breaks when booting with nosmp

Hi Jesse,

Le lundi 21 avril 2008, Jesse Barnes a écrit :
> On Monday, April 21, 2008 2:09 pm Andi Kleen wrote:
> > > Both call disable_ioapic_setup(), so how can they not be the same?
> >
> > See Jesse's explanation. Basically there is special code in the smp
> > boot up to handle 0 CPUs and it disables all APICs.
> >
> > This is very old and crufty and somewhat obsolete logic,
> > but it is like that.
> 
> This might be closer to a real fix.  Can you confirm that this works for you 
> Jean?
> 
> Thanks,
> Jesse
> 
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index e6abe8a..7cdf930 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1138,14 +1138,10 @@ static int __init smp_sanity_check(unsigned max_cpus)
>  				 "forcing use of dummy APIC emulation.\n");
>  		smpboot_clear_io_apic();
>  #ifdef CONFIG_X86_32
> -		if (nmi_watchdog == NMI_LOCAL_APIC) {
> -			printk(KERN_INFO "activating minimal APIC for"
> -					 "NMI watchdog use.\n");
> -			connect_bsp_APIC();
> -			setup_local_APIC();
> -			end_local_APIC_setup();
> -		}
> +		connect_bsp_APIC();
>  #endif
> +		setup_local_APIC();
> +		end_local_APIC_setup();
>  		return -1;
>  	}
>  
> 

Sorry for the late reply. I tested the patch above on top of 2.6.25-git4
and yes, it fixes my problem: booting with "nosmp" works now. Thanks!

Is this patch good enough to go upstream, and if so, through whose
tree? Adding Thomas Gleixner to Cc.

-- 
Jean Delvare
Suse L3
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