Re: [BUGFIX v2 2/4] ACPI, DOCK: resolve possible deadlock scenarios

From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Jiang Liu <liuj97@gmail.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
	Yinghai Lu <yinghai@kernel.org>,
	"Alexander E . Patrakov" <patrakov@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Yijing Wang <wangyijing@huawei.com>,
	linux-acpi@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org, Len Brown <lenb@kernel.org>,
	stable@vger.kernel.org, Jiang Liu <jiang.liu@huawei.com>
Subject: Re: [BUGFIX v2 2/4] ACPI, DOCK: resolve possible deadlock scenarios
Date: Sun, 16 Jun 2013 00:54:59 +0200	[thread overview]
Message-ID: <2139297.LeMhgEjsya@vostro.rjw.lan> (raw)
In-Reply-To: <18797091.iPZsNWFGi1@vostro.rjw.lan>

On Saturday, June 15, 2013 11:20:40 PM Rafael J. Wysocki wrote:
> On Saturday, June 15, 2013 10:17:42 PM Rafael J. Wysocki wrote:

[...]

> 
> Which sysfs interfaces do you mean, by the way?
> 
> If you mean "eject", then it takes acpi_scan_lock and hotplug_dock_devices()
> should always be run under acpi_scan_lock too.  It isn't at the moment,
> because write_undock() doesn't take acpi_scan_lock(), but this is an obvious
> bug (so I'm going to send a patch to fix it in a while).
> 
> With that bug fixed, the possible race between acpi_eject_store() and
> hotplug_dock_devices() should be prevented from happening, so perhaps we're
> worrying about something that cannot happen?

So here's a question: What particular races are possible if we remove
ds->hp_lock entirely without doing anything else just yet?  I mean, how to
*trigger* them from the start to the end and not how they can possibly happen
but never do, because there's no way they can be actually triggered?

Rafael

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