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

Moore, Robert
2013-02-14T20:45:14Z

> -----Original Message-----
> From: Rafael J. Wysocki [mailto:rjw@sisk.pl]
> 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@vger.kernel.org
> 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.
Bob

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