Adding Len because this should probably go through his tree, not Jesse's. Len, we're discussing a patch that I feel should go into 2.6.30, because it fixes an oops that I introduced in the beginning of the merge window, and that we've been working on since. We just now have a patch to fix it, along with another patch that I wrote: http://patchwork.kernel.org/patch/25296/ This current patch is here: http://patchwork.kernel.org/patch/25895/ Discussion follows. * Bjorn Helgaas <bjorn.helgaas@xxxxxx>: > On Monday 25 May 2009 06:08:03 pm Kenji Kaneshige wrote: > > Fix wrong struct pci_dev reference counter handling in acpi_pci_bind(). > > > > The 'dev' field of struct acpi_pci_data is having a pointer to struct > > pci_dev without incrementing the reference counter. Because of this, I > > got the following kernel oops when I was doing some pci hotplug > > operations. This patch fixes this bug by replacing wrong hand-made > > pci_find_slot() with pci_get_slot() in acpi_pci_bind(). > > I don't like this ACPI/PCI bind thing in general because having the > extra .bind and .unbind methods is ugly and somewhat non-obvious, and > I'm nervous about object lifetime issues like this one. > > But I don't have a better alternative to offer, and there's definitely > a problem here, so thanks for fixing and testing it. I do have one > question below about whether the comment in the existing code, which > seems to be an excuse for doing the hand-made pci_find_slot(), is > still relevant, or should just be removed. I reviewed and successfully tested this patch on our ia64 machine. Reviewed-by: Alex Chiang <achiang@xxxxxx> Tested-by: Alex Chiang <achiang@xxxxxx> > > @@ -180,16 +177,8 @@ int acpi_pci_bind(struct acpi_device *de > > * PCI devices are added to the global pci list when the root > > * bridge start ops are run, which may not have happened yet. > > Please update or remove this comment, which claims that "we cannot > simply search the global pci device list." I don't know whether the > comment (a) explains why we can't use pci_get_slot(), (b) explains > why we can't use pci_find_slot() or some other interface, (c) refers > to an ordering problem that doesn't exist on your system, or (d) is > just no longer applicable at all. I think the comment is simply no longer applicable. During boot, we exercise this path in acpi_pci_root_add(): acpi_pci_root_add pci_acpi_scan_root acpi_pci_bind_root acpi_pci_bridge_scan acpi_pci_bind pci_acpi_scan_root will create the PCI namespace for us before we attempt to bind the devices, so we know we will find the pci_dev on the pci_bus->devices list. During hotplug, we exercise this path: acpiphp_enable_slot enable_device pci_scan_slot pci_scan_bridge acpiphp_bus_add acpi_bus_add acpi_add_single_object acpi_pci_bind pci_scan_slot() will put the new pci_devs onto pci_bus->devices, so by the time we get to acpi_pci_bind, the call to pci_get_slot will be successful. There is the case where we hotplug a bridge device: handle_hotplug_event_bridge handle_bridge_insertion acpi_bus_add acpi_add_single_object acpi_pci_bind And this does confuse me a little bit, because I'm not seeing how the bridge device gets added to the parent pci_bus->devices list before we get to acpi_pci_bind, but... Kenji's patch isn't changing the semantics on _how_ we find a device: - bus = pci_find_bus(data->id.segment, data->id.bus); - if (bus) { - list_for_each_entry(dev, &bus->devices, bus_list) { - if (dev->devfn == PCI_DEVFN(data->id.device, - data->id.function)) { - data->dev = dev; - break; - } - } - } + data->dev = pci_get_slot(pdata->bus, + PCI_DEVFN(data->id.device, data->id.function)); if (!data->dev) { ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Device %04x:%02x:%02x.%d not present in PCI namespace\n", pci_get_slot() iterates across bus->devices too (except that it correctly grabs the pci_bus_sem first) in addition to the obvious refcount on the pci_dev. Given the above, I feel pretty comfortable with Kenji-san's change, and I'd recommend that he just get rid of that confusing comment entirely. The only other suggestion I have is that he could trim down the oops output a bit to just get the stack trace: BUG: unable to handle kernel NULL pointer dereference at 00000000000000e8 IP: [<ffffffff803f0e9b>] acpi_pci_unbind+0xb1/0xdd Call Trace: [<ffffffff803ecee4>] acpi_bus_remove+0x54/0x68 [<ffffffff803ecf6d>] acpi_bus_trim+0x75/0xe3 [<ffffffffa0345ddd>] acpiphp_disable_slot+0x16d/0x1e0 [acpiphp] [<ffffffffa03441f0>] disable_slot+0x20/0x60 [acpiphp] [<ffffffff803cfc18>] power_write_file+0xc8/0x110 [<ffffffff803c6a54>] pci_slot_attr_store+0x24/0x30 [<ffffffff803469ce>] sysfs_write_file+0xce/0x140 [<ffffffff802e94e7>] vfs_write+0xc7/0x170 [<ffffffff802e9aa0>] sys_write+0x50/0x90 [<ffffffff8020bd6b>] system_call_fastpath+0x16/0x1b Thanks. /ac -- 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
