On Fri, May 11, 2012 at 8:00 AM, Jiang Liu <liuj97@xxxxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html