Date: Tue, 8 Jul 2014 09:41:49 +0200
From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
To: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Paolo Pisati <p.pisati@gmail.com>, Andrew Lunn <andrew@lunn.ch>,
        Jason Cooper <jason@lakedaemon.net>, Joerg Roedel <joro@8bytes.org>,
        Hiroshi.DOYU@nokia.com, linux-kernel@vger.kernel.org,
        iommu@lists.linux-foundation.org,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Gregory CLEMENT <gregory.clement@free-electrons.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>,
        Florian Vaussard <florian.vaussard@epfl.ch>,
        linux-arm-kernel@lists.infradead.org
Subject: Re: 3.16rc3 multiplatform, Armada 370 and IOMMU: unbootable kernel
Message-ID: <20140708094149.0ad6ab13@free-electrons.com>
In-Reply-To: <20140707233758.GA1456@arch.cereza>
References: <20140703135146.GA6898@luxor.wired.org>
	<53B5C61D.2060308@free-electrons.com>
	<53B5CA26.7050405@free-electrons.com>
	<1936558.QaAG1bYMuD@avalon>
	<20140705150308.GA28791@arch.cereza>
	<20140705205951.GB3678@kroah.com>
	<20140707105818.GA1101@arch.cereza>
	<20140707183002.GA5947@kroah.com>
	<20140707233758.GA1456@arch.cereza>
Organization: Free Electrons
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Sender: linux-kernel-owner@vger.kernel.org

Dear Ezequiel Garcia,

On Mon, 7 Jul 2014 20:37:58 -0300, Ezequiel Garcia wrote:

> It seems bus_register_notifier() is been called for platform and pci devices
> with the *same* notifier block. Haven't looked close enough, but you mentioned
> that could cause trouble?
> 
> This patch fixes the issue here:
> 
> diff --git a/arch/arm/mach-mvebu/coherency.c b/arch/arm/mach-mvebu/coherency.c
> index 477202f..2bdc323 100644
> --- a/arch/arm/mach-mvebu/coherency.c
> +++ b/arch/arm/mach-mvebu/coherency.c
> @@ -292,6 +292,10 @@ static struct notifier_block mvebu_hwcc_nb = {
>  	.notifier_call = mvebu_hwcc_notifier,
>  };
>  
> +static struct notifier_block mvebu_hwcc_pci_nb = {
> +	.notifier_call = mvebu_hwcc_notifier,
> +};
> +
>  static void __init armada_370_coherency_init(struct device_node *np)
>  {
>  	struct resource res;
> @@ -427,7 +431,7 @@ static int __init coherency_pci_init(void)
>  {
>  	if (coherency_available())
>  		bus_register_notifier(&pci_bus_type,
> -				       &mvebu_hwcc_nb);
> +				       &mvebu_hwcc_pci_nb);
>  	return 0;
>  }
>  
> Paolo, can you apply it and confirm it fixes the problem?
> 
> Greg, can you confirm using the same notifier block pointer
> for two different bus types makes the bus notifier go nuts?

Looking at how notifier_chain_register() is implemented (which gets
called by bus_register_notifier() ->
blocking_notifier_chain_register()), I indeed don't see how a single
'struct notifier_block' can be registered on multiple notifier chains,
so I believe your patch is correct.

Thanks for the investigation!

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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