linux-kernel - Re: [PATCH 2/2] ACPI / hotplug: Remove containers synchronously

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Date:	Wed, 28 Aug 2013 11:53:50 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>, Gu Zheng <guz.fnst@...fujitsu.com>,
	Toshi Kani <toshi.kani@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Subject: Re: [PATCH 2/2] ACPI / hotplug: Remove containers synchronously

On Wed, Aug 28, 2013 at 03:51:41PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> The current protocol for handling hot remove of containers is very
> fragile and causes acpi_eject_store() to acquire acpi_scan_lock
> which may deadlock with the removal of the device that it is called
> for (the reason is that device sysfs attributes cannot be removed
> while their callbacks are being executed and ACPI device objects
> are removed under acpi_scan_lock).
> 
> The problem is related to the fact that containers are handled by
> acpi_bus_device_eject() in a special way, which is to emit an
> offline uevent instead of just removing the container.  Then, user
> space is expected to handle that uevent and use the container's
> "eject" attribute to actually remove it.  That is fragile, because
> user space may fail to complete the ejection (for example, by not
> using the container's "eject" attribute at all) leaving the BIOS
> kind of in a limbo.  Moreover, if the eject event is not signaled
> for a container itself, but for its parent device object (or
> generally, for an ancestor above it in the ACPI namespace), the
> container will be removed straight away without doing that whole
> dance.
> 
> For this reason, modify acpi_bus_device_eject() to remove containers
> synchronously like any other objects (user space will get its uevent
> anyway in case it does some other things in response to it) and
> remove the eject_pending ACPI device flag that is not used any more.
> This way acpi_eject_store() doesn't have a reason to acquire
> acpi_scan_lock any more and one possible deadlock scenario goes
> away (plus the code is simplified a bit).
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Reported-by: Gu Zheng <guz.fnst@...fujitsu.com>

Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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