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SubjectRe: [PATCH v2 8/8] PCI: pciehp: Check that the device is really present before touching it
On Fri, Oct 13, 2017 at 09:35:48PM +0300, Mika Westerberg wrote:
> During surprise hot-unplug the device is not there anymore. When that
> happens we read 0xffffffff from the registers and pciehp_unconfigure_device()
> inadvertently thinks the device is a display device because bridge
> control register returns 0xff refusing to remove it:
>
> pciehp 0000:00:1c.0:pcie004: Slot(0): Link Down
> pciehp 0000:00:1c.0:pcie004: Slot(0): Card present
> pciehp 0000:00:1c.0:pcie004: Cannot remove display device 0000:01:00.0
>
> This causes the hotplug functionality to leave the hierarcy untouched
> preventing further hotplug operations.
>
> To fix this verify presence of a device by calling pci_device_is_present()
> for it before we touch it any further.
>
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
> drivers/pci/hotplug/pciehp_pci.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c
> index 2a1ca020cf5a..fb4333168e23 100644
> --- a/drivers/pci/hotplug/pciehp_pci.c
> +++ b/drivers/pci/hotplug/pciehp_pci.c
> @@ -100,8 +100,14 @@ int pciehp_unconfigure_device(struct slot *p_slot)
> */
> list_for_each_entry_safe_reverse(dev, temp, &parent->devices,
> bus_list) {
> + bool present;
> +
> pci_dev_get(dev);
> - if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE && presence) {
> +
> + /* Check if the device is really there anymore */
> + present = presence ? pci_device_is_present(dev) : false;
> +
> + if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE && present) {
> pci_read_config_byte(dev, PCI_BRIDGE_CONTROL, &bctl);

I don't like this fix because it's still racy. We always have to be deal
with a config read that returns 0xffffffff, even if we previously checked
pci_device_is_present(). The device might have disappeared in the interim.

> if (bctl & PCI_BRIDGE_CTL_VGA) {
> ctrl_err(ctrl,
> @@ -112,7 +118,7 @@ int pciehp_unconfigure_device(struct slot *p_slot)
> break;
> }
> }
> - if (!presence) {
> + if (!present) {
> pci_dev_set_disconnected(dev, NULL);
> if (pci_has_subordinate(dev))
> pci_walk_bus(dev->subordinate,
> @@ -123,7 +129,7 @@ int pciehp_unconfigure_device(struct slot *p_slot)
> * Ensure that no new Requests will be generated from
> * the device.
> */
> - if (presence) {
> + if (present) {
> pci_read_config_word(dev, PCI_COMMAND, &command);
> command &= ~(PCI_COMMAND_MASTER | PCI_COMMAND_SERR);
> command |= PCI_COMMAND_INTX_DISABLE;
> --
> 2.14.2
>

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