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From:   Daniel Axtens <dja@axtens.net>
To:     Tyrel Datwyler <tyreld@linux.ibm.com>, mpe@ellerman.id.au
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        Tyrel Datwyler <tyreld@linux.ibm.com>
Subject: Re: [PATCH] powerpc/pseries: extract host bridge from pci_bus prior to bus removal
In-Reply-To: <20210211182435.47968-1-tyreld@linux.ibm.com>
References: <20210211182435.47968-1-tyreld@linux.ibm.com>
Date:   Fri, 16 Apr 2021 17:15:00 +1000
Message-ID: <878s5ig0p7.fsf@linkitivity.dja.id.au>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Hi Tyrel,

> The pci_bus->bridge reference may no longer be valid after
> pci_bus_remove() resulting in passing a bad value to device_unregister()
> for the associated bridge device.
>
> Store the host_bridge reference in a separate variable prior to
> pci_bus_remove().
>
The patch certainly seems to do what you say. I'm not really up on the
innards of PCI, so I'm struggling to figure out by what code path
pci_bus_remove() might invalidate pci_bus->bridge? A quick look at
pci_remove_bus was not very illuminating but I didn't chase down every
call it made.

Kind regards,
Daniel

> Fixes: 7340056567e3 ("powerpc/pci: Reorder pci bus/bridge unregistration during PHB removal")
> Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/pci_dlpar.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/platforms/pseries/pci_dlpar.c b/arch/powerpc/platforms/pseries/pci_dlpar.c
> index f9ae17e8a0f4..a8f9140a24fa 100644
> --- a/arch/powerpc/platforms/pseries/pci_dlpar.c
> +++ b/arch/powerpc/platforms/pseries/pci_dlpar.c
> @@ -50,6 +50,7 @@ EXPORT_SYMBOL_GPL(init_phb_dynamic);
>  int remove_phb_dynamic(struct pci_controller *phb)
>  {
>  	struct pci_bus *b = phb->bus;
> +	struct pci_host_bridge *host_bridge = to_pci_host_bridge(b->bridge);
>  	struct resource *res;
>  	int rc, i;
>  
> @@ -76,7 +77,8 @@ int remove_phb_dynamic(struct pci_controller *phb)
>  	/* Remove the PCI bus and unregister the bridge device from sysfs */
>  	phb->bus = NULL;
>  	pci_remove_bus(b);
> -	device_unregister(b->bridge);
> +	host_bridge->bus = NULL;
> +	device_unregister(&host_bridge->dev);
>  
>  	/* Now release the IO resource */
>  	if (res->flags & IORESOURCE_IO)
> -- 
> 2.27.0