Re: [PATCH -v3 40/47] PCI: Add pci bus removal through /sys/.../pci_bus/.../remove

[Jiang Liu]

Hi Yinghai,
	I found many other drivers assume that a pci bus won't disappear if
the corresponding PCI bridge device still exists. The sysfs interface proposed
here breaks that assumption and may cause many access-after-free issues.
So what's the purpose of this interface? Should we remove this interface or
enhance other drivers to avoid invalid memory access issues?
	Thanks!
	Gerry
 
On 03/19/2012 01:46 PM, Yinghai Lu wrote:
> it supports both pci root bus and pci bus under pci bridge.
> 
> -v2: Change to three returns way in dev_bus_remove_store.
> 
> Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: linux-doc@xxxxxxxxxxxxxxx
> ---
>  Documentation/ABI/testing/sysfs-bus-pci |    8 ++++++++
>  drivers/pci/pci-sysfs.c                 |   30 ++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+), 0 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> index 95f0f37..22392de 100644
> --- a/Documentation/ABI/testing/sysfs-bus-pci
> +++ b/Documentation/ABI/testing/sysfs-bus-pci
> @@ -92,6 +92,14 @@ Description:
>  		hot-remove the PCI device and any of its children.
>  		Depends on CONFIG_HOTPLUG.
>  
> +What:		/sys/bus/pci/devices/.../pci_bus/.../remove
> +Date:		March 2012
> +Contact:	Linux PCI developers <linux-pci@xxxxxxxxxxxxxxx>
> +Description:
> +		Writing a non-zero value to this attribute will
> +		hot-remove the PCI bus and any of its children.
> +		Depends on CONFIG_HOTPLUG.
> +
>  What:		/sys/bus/pci/devices/.../pci_bus/.../rescan
>  Date:		May 2011
>  Contact:	Linux PCI developers <linux-pci@xxxxxxxxxxxxxxx>
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index d33a1bc..afba77b 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -391,6 +391,35 @@ remove_store(struct device *dev, struct device_attribute *dummy,
>  	return count;
>  }
>  
> +static void bus_remove_callback(struct device *dev)
> +{
> +	struct pci_bus *bus = to_pci_bus(dev);
> +
> +	mutex_lock(&pci_remove_rescan_mutex);
> +	pci_stop_and_remove_bus(bus);
> +	mutex_unlock(&pci_remove_rescan_mutex);
> +}
> +static ssize_t
> +dev_bus_remove_store(struct device *dev, struct device_attribute *attr,
> +		 const char *buf, size_t count)
> +{
> +	int err;
> +	unsigned long val;
> +
> +	if (kstrtoul(buf, 0, &val) < 0)
> +		return -EINVAL;
> +
> +	if (!val)
> +		return count;
> +
> +	err = device_schedule_callback(dev, bus_remove_callback);
> +
> +	if (err)
> +		return err;
> +
> +	return count;
> +}
> +
>  static void bus_rescan_callback(struct device *dev)
>  {
>  	struct pci_bus *bus = to_pci_bus(dev);
> @@ -450,6 +479,7 @@ struct device_attribute pci_dev_attrs[] = {
>  struct device_attribute pcibus_dev_attrs[] = {
>  #ifdef CONFIG_HOTPLUG
>  	__ATTR(rescan, (S_IWUSR|S_IWGRP), NULL, dev_bus_rescan_store),
> +	__ATTR(remove, (S_IWUSR|S_IWGRP), NULL, dev_bus_remove_store),
>  #endif
>  	__ATTR(cpuaffinity, S_IRUGO, pci_bus_show_cpumaskaffinity, NULL),
>  	__ATTR(cpulistaffinity, S_IRUGO, pci_bus_show_cpulistaffinity, NULL),

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