Re: [RFC PATCH v2, part3 07/11] PCI, xen-pcifront: use new PCI interfacesto simplify implementation

From: Jiang Liu
Date: Sun Jun 09 2013 - 12:51:03 EST

On Sat 08 Jun 2013 01:07:06 AM CST, Konrad Rzeszutek Wilk wrote:
> On Sat, Jun 08, 2013 at 12:50:31AM +0800, Jiang Liu wrote:
>> On 06/07/2013 11:38 PM, Konrad Rzeszutek Wilk wrote:
>>> On Fri, Jun 07, 2013 at 10:50:24AM -0400, Konrad Rzeszutek Wilk wrote:
>>>> On Thu, May 16, 2013 at 11:50:55PM +0800, Jiang Liu wrote:
>>>>> Use new PCI interfaces to simplify xen-pcifront implementation:
>>>>> 1) Use pci_create_root_bus() instead of pci_scan_bus_parented()
>>>>> because pci_scan_bus_parented() is marked as __deprecated.This
>>>>> also gets rid of a duplicated call of pci_bus_start_devices().
>>>>> 2) Use pci_stop_root_bus() and pci_remove_root_bus() instead of
>>>>> open-coded private implementation.
>>>>> 3) Use pci_set_host_bridge_release() to release data structures
>>>>> associated with PCI root buses.
>>>>> 4) Use pci_bus_get()/pci_bus_put() to manage PCI root bus reference
>>>>> count.
>>>>> This is also a preparation for coming PCI bus lock enhancement.
>>> With this patch from :
>>> Merge branch 'pci_lock_v3' of into testing
>>> it blows up when detaching the device.
>> Hi Konrad,
>> Thanks for testing! According to the log messages, this issue should
>> be related to pci bus reference counter management. Seems we have done
>> an extra(unbalanced) release of pci bus device.
>> Will investigate it tomorrow!
> That is quite commendable that you are willing to look over this on
> the weekend but I am not going to be able to rerun this test until
> some time in the week. You could enjoy the weekend and just look at
> this during the week.

Hi Konrad,
We should have root-caused this bug, which is caused by
Current implementation doesn't support root bus deletion when walking
PCI root
buses by for_each_pci_root_bus(). The reference counter
becomes zero after returning from pci_remove_root_bus(), so it triggers
kref warnings
and double-free of klist_node object when we call
pci_get_next_root_bus() to get the
next PCI root bus.
So we will first revert to list_for_each_entry_safe(bus, temp,
&pci_root_buses, node)
and solve this issue in next version of for_each_pci_root_bus().


diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c
index 6aa2c0f..6e577db 100644
--- a/drivers/pci/xen-pcifront.c
+++ b/drivers/pci/xen-pcifront.c
@@ -553,11 +553,11 @@ static int pcifront_rescan_root(struct
pcifront_device *pdev,
static void pcifront_free_roots(struct pcifront_device *pdev)
struct pcifront_sd *sd;
- struct pci_bus *bus;
+ struct pci_bus *bus, *temp;

dev_dbg(&pdev->xdev->dev, "cleaning up root buses\n");

- for_each_pci_root_bus(bus) {
+ list_for_each_entry_safe(bus, temp, &pci_root_buses, node) {
sd = bus->sysdata;
if (sd->pdev == pdev) {

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