On 06/17/2013 07:39 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,t >>> 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? Hi Rafael, Seems we can't rely on acpi_scan_lock here, it may cause another deadlock scenario: 1) thread 1 acquired the acpi_scan_lock and tries to destroy all sysfs interfaces for PCI devices. 2) thread 2 opens a PCI sysfs which then tries to acquire the acpi_scan_lock. Regards! Gerry > > Rafael > > -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html