On Monday, June 17, 2013 01:39:04 PM Rafael J. Wysocki wrote: > On Monday, June 17, 2013 01:01:51 AM Jiang Liu wrote: > > On 06/16/2013 05:20 AM, Rafael J. Wysocki wrote: > > > On Saturday, June 15, 2013 10:17:42 PM Rafael J. Wysocki wrote: > > >> On Saturday, June 15, 2013 09:44:28 AM Jiang Liu wrote: > > [...] > > >> When it returns from unregister_hotplug_dock_device(), nothing prevents it > > >> from accessing whatever it wants, because ds->hp_lock is not used outside > > >> of the add/del and hotplug_dock_devices(). So, the actual role of > > >> ds->hp_lock (not the one that it is supposed to play, but the real one) > > >> is to prevent addition/deletion from happening when hotplug_dock_devices() > > >> is running. [Yes, it does protect the list, but since the list is in fact > > >> unnecessary, that doesn't matter.] > > >> > > >>> If we simply use a flag to mark presence of registered callback, we > > >>> can't achieve the second goal. > > >> > > >> I don't mean using the flag *alone*. > > >> > > >>> Take the sony laptop as an example. It has several PCI > > >>> hotplug > > >>> slot associated with the dock station: > > >>> [ 28.829316] acpiphp_glue: _handle_hotplug_event_func: Bus check > > >>> notify on \_SB_.PCI0.RP07.LPMB > > >>> [ 30.174964] acpiphp_glue: _handle_hotplug_event_func: Bus check > > >>> notify on \_SB_.PCI0.RP07.LPMB.LPM0 > > >>> [ 30.174973] acpiphp_glue: _handle_hotplug_event_func: Bus check > > >>> notify on \_SB_.PCI0.RP07.LPMB.LPM1 > > >>> [ 30.174979] acpiphp_glue: _handle_hotplug_event_func: Bus check > > >>> notify on \_SB_.PCI0.RP07.LPMB.LPM2 > > >>> [ 30.174985] acpiphp_glue: _handle_hotplug_event_func: Bus check > > >>> notify on \_SB_.PCI0.RP07.LPMB.LPM2.LPRI.LPR0.GFXA > > >>> [ 30.175020] acpiphp_glue: _handle_hotplug_event_func: Bus check > > >>> notify on \_SB_.PCI0.RP07.LPMB.LPM2.LPRI.LPR0.GHDA > > >>> [ 30.175040] acpiphp_glue: _handle_hotplug_event_func: Bus check > > >>> notify on \_SB_.PCI0.RP07.LPMB.LPM2.LPRI.LPR1.LPCI.LPC0.DLAN > > >>> [ 30.175050] acpiphp_glue: _handle_hotplug_event_func: Bus check > > >>> notify on \_SB_.PCI0.RP07.LPMB.LPM2.LPRI.LPR1.LPCI.LPC1.DODD > > >>> [ 30.175060] acpiphp_glue: _handle_hotplug_event_func: Bus check > > >>> notify on \_SB_.PCI0.RP07.LPMB.LPM2.LPRI.LPR1.LPCI.LPC2.DUSB > > >>> > > >>> So it still has some race windows if we undock the station while > > >>> repeatedly rescanning/removing > > >>> the PCI bus for \_SB_.PCI0.RP07.LPMB.LPM0 through sysfs interfaces. > > > > > > Which sysfs interfaces do you mean, by the way? > > > > > > If you mean "eject", then it takes acpi_scan_lock and hotplug_dock_devices() > > > should always be run under acpi_scan_lock too. It isn't at the moment, > > > because write_undock() doesn't take acpi_scan_lock(), but this is an obvious > > > bug (so I'm going to send a patch to fix it in a while). > > > > > > With that bug fixed, the possible race between acpi_eject_store() and > > > hotplug_dock_devices() should be prevented from happening, so perhaps we're > > > worrying about something that cannot happen? > > Hi Rafael, > > I mean the "remove" method of each PCI device, and the "power" method > > of PCI hotplug slot here. > > These methods may be used to remove P2P bridges with associated ACPIPHP > > hotplug slots, which in turn will cause invoking of > > unregister_hotplug_dock_device(). > > So theoretical we may trigger the bug by undocking while repeatedly > > adding/removing P2P bridges with ACPIPHP hotplug slot through PCI > > "rescan" and "remove" sysfs interface, > > Why don't we make these things take acpi_scan_lock upfront, then? Or perhaps (and maybe better) why don't we replace ds->hp_lock by another lock that will be acquired upper in the call chain so that dock_add_hotplug_device(), dock_del_hotplug_device(), hotplug_dock_devices() and dock_event() are all guaranteed to be called under that lock? Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- 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
