Alex Chiang wrote: > 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 just no longer applicable at all.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 I think the comment is simply no longer applicable.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 > Thank you very much for detailed analysis. I agree with you. I'll send an updated patch (instead of additional patch to remove obsolete comment), but it will be tomorrow because I'm day off today. Sorry... Thanks, Kenji Kaneshige -- 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
