Re: [Update][PATCH] ACPI / hotplug: Fix concurrency issues and memory leaks

Rafael J. Wysocki
2013-02-14T12:03:57Z

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?

Rafael

--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.