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

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Message-ID: <7482249.JD6lNDApdo@vostro.rjw.lan>
Date:	Thu, 14 Feb 2013 21:59:25 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Moore, Robert" <robert.moore@...el.com>
Cc:	Toshi Kani <toshi.kani@...com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jiang Liu <liuj97@...il.com>, Yinghai Lu <yinghai@...nel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Myron Stowe <mstowe@...hat.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
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@...k.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@...r.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.

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.

Thanks,
Rafael


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