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

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Date:	Thu, 14 Feb 2013 13:03:57 +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 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.
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