> -----Original Message----- > From: Rafael J. Wysocki [mailto:rjw@xxxxxxx] > Sent: Thursday, February 14, 2013 12:59 PM > To: Moore, Robert > Cc: Toshi Kani; ACPI Devel Maling List; LKML; Bjorn Helgaas; Jiang Liu; > Yinghai Lu; Yasuaki Ishimatsu; Myron Stowe; linux-pci@xxxxxxxxxxxxxxx > Subject: Re: [Update][PATCH] ACPI / hotplug: Fix concurrency issues and > memory leaks > > On Thursday, February 14, 2013 08:45:14 PM Moore, Robert wrote: > > > > > -----Original Message----- > > > From: Rafael J. Wysocki [mailto:rjw@xxxxxxx] > > > Sent: Thursday, February 14, 2013 4:04 AM > > > To: Moore, Robert > > > Cc: Toshi Kani; ACPI Devel Maling List; LKML; Bjorn Helgaas; Jiang > > > Liu; Yinghai Lu; Yasuaki Ishimatsu; Myron Stowe; > > > linux-pci@xxxxxxxxxxxxxxx > > > Subject: Re: [Update][PATCH] ACPI / hotplug: Fix concurrency issues > > > and memory leaks > > > > > > On Thursday, February 14, 2013 02:31:22 AM Moore, Robert wrote: > > > > > > > I thought about that, but actually there's no guarantee that > > > > > > > the handle will be valid after _EJ0 as far as I can say. So > > > > > > > the race condition is going to be there anyway and using > > > > > > > struct acpi_device just makes it easier to avoid it. > > > > > > > > > > > > In theory, yes, a stale handle could be a problem, if _EJ0 > > > > > > performs unload table and if ACPICA frees up its internal data > > > > > > structure pointed by the handle as a result. But we should > > > > > > not see such issue now since we do not support dynamic ACPI > > > > > > namespace > > > yet. > > > > > > > > > > I'm waiting for information from Bob about that. If we can > > > > > assume ACPI handles to be always valid, that will simplify > > > > > things quite a > > > bit. > > > > > > > > If a table is unloaded, all the namespace nodes for that table are > > > > removed from the namespace, and thus any ACPI_HANDLE pointers go > > > > stale > > > and invalid. > > > > > > OK, thanks! > > > > > > To me this means that we cannot assume a handle to stay valid > > > between a notify handler and acpi_bus_hot_remove_device() run from a > workqueue. > > > > > > Is there a mechanism in ACPICA to ensure that a handle won't become > > > stale while a notify handler is running for it or is the OS > > > responsible for ensuring that > > > _EJ0 won't be run in parallel with notify handlers for device > > > objects being ejected? > > > > > > > It is up to the host. > > I was afraid that that might be the case. :-) > > So far the (Linux) host has been happily ignoring that potential problem, > so I guess it can still be ignored for a while, although we'll need to > address it eventually at one point. I would think it should be fairly simple to setup a mechanism to either tell the driver or for the driver to figure it out -- such that the driver knows that all handles associated with the device are now invalid. Another way to look at it is that when the device is re-installed, the driver should reinitialize such that it obtains new handles for the devices and subobjects in question. Bob > > Thanks, > Rafael > > > -- > I speak only for myself. > Rafael J. Wysocki, Intel Open Source Technology Center. ��.n��������+%������w��{.n�����{���"�)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
