On Fri, May 11, 2012 at 8:00 AM, Jiang Liu liuj97@gmail.com wrote:
On 05/11/2012 08:24 AM, Amos Kong wrote:
On 05/11/2012 07:54 AM, Amos Kong wrote:
On 05/11/2012 02:55 AM, Michael S. Tsirkin wrote:
On Fri, May 11, 2012 at 01:09:13AM +0800, Jiang Liu wrote:
On 05/10/2012 11:44 PM, Amos Kong wrote:
diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c index 806c44f..a7442d9 100644 --- a/drivers/pci/hotplug/acpiphp_glue.c +++ b/drivers/pci/hotplug/acpiphp_glue.c @@ -885,7 +885,7 @@ static void disable_bridges(struct pci_bus *bus) static int disable_device(struct acpiphp_slot *slot) { struct acpiphp_func *func;
- struct pci_dev *pdev;
- struct pci_dev *pdev, *tmp;
struct pci_bus *bus = slot->bridge->pci_bus;
/* The slot will be enabled when func 0 is added, so check @@ -902,9 +902,10 @@ static int disable_device(struct acpiphp_slot *slot) func->bridge = NULL; }
- pdev = pci_get_slot(slot->bridge->pci_bus,
- PCI_DEVFN(slot->device, func->function));
- if (pdev) {
- list_for_each_entry_safe(pdev, tmp, &bus->devices, bus_list) {
- if (PCI_SLOT(pdev->devfn) != slot->device)
- continue;
I think the concept is good: in enable_device(), we use pci_scan_slot(), which scans all possible functions in the slot. So in disable_device() we should do something symmetric to remove all the functions.
The pci_bus_sem lock should be acquired when walking the bus->devices list. Otherwise it may cause invalid memory access if another thread is modifying the bus->devices list concurrently.
pci_bus_sem lock is only request for writing &bus->devices list, right ? and this protection already exists in pci_destory_dev().
That's for writer. For reader to walk the pci_bus->devices list, you also need to acquire the reader lock by down_read(&pci_bus_sem). Please refer to pci_get_slot() for example. This especially import for native OS because there may be multiple PCI slots/devices on the bus.
There is a lot of existing code that walks bus->devices without holding pci_bus_sem, but most of it is boot-time code that is arguably safe (though I think things like pcibios_fixup_bus() are poorly designed and don't fit well in the hotplug-enabled world).
In this case, I do think we need to protect against updates while we're walking bus->devices. It's probably not trivial because __pci_remove_bus_device() calls pci_destroy_dev(), where we do the down_write(), so simply wrapping the whole thing with down_read() will cause a deadlock.
Kenji-san, Yinghai, do you have any input?
Bjorn