Re: [PATCH] powerpc/pseries: extract host bridge from pci_bus prior to bus removal
On Thu, 11 Feb 2021 12:24:35 -0600, Tyrel Datwyler wrote: > 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(). Applied to powerpc/next. [1/1] powerpc/pseries: extract host bridge from pci_bus prior to bus removal https://git.kernel.org/powerpc/c/38d0b1c9cec71e6d0f3bddef0bbce41d05a3e796 cheers
Re: [PATCH] powerpc/pseries: extract host bridge from pci_bus prior to bus removal
On 4/16/21 12:15 AM, Daniel Axtens wrote:
> 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.
remove_phb_dynamic()
|--> pci_remove_bus(bus)
|--> device_unregister(>dev)
|--> put_device(dev)
|--> device_release(kobj)
|--> dev->class->dev_release(dev) == release_pci_bus(dev)
|--> kfree(bus)
We have the above call chain that takes place in the when put_device() triggers
the kobject ref count to go zero. The kobject_release function in this case is
device_release() which in turn calls dev->class->dev_release(dev). For a pci_bus
the class is appropriately pcibus_class whose dev_release() callback points to
release_pci_bus(). This in turn calls kfree() on the bus. Which means we can no
longer safely dereference any fields of the pci_bus struct.
-Tyrel
>
> Kind regards,
> Daniel
>
>> Fixes: 7340056567e3 ("powerpc/pci: Reorder pci bus/bridge unregistration
>> during PHB removal")
>> Signed-off-by: Tyrel Datwyler
>> ---
>> 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(_bridge->dev);
>>
>> /* Now release the IO resource */
>> if (res->flags & IORESOURCE_IO)
>> --
>> 2.27.0
Re: [PATCH] powerpc/pseries: extract host bridge from pci_bus prior to bus removal
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
> ---
> 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(_bridge->dev);
>
> /* Now release the IO resource */
> if (res->flags & IORESOURCE_IO)
> --
> 2.27.0
Re: [PATCH] powerpc/pseries: extract host bridge from pci_bus prior to bus removal
On 2/11/21 10:24 AM, Tyrel Datwyler wrote:
> 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().
>
> Fixes: 7340056567e3 ("powerpc/pci: Reorder pci bus/bridge unregistration
> during PHB removal")
> Signed-off-by: Tyrel Datwyler
Ping?
