linux-kernel - Re: [PATCH 2/3] firmware: Avoid deadlock of usermodehelper lock at shutdown

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Message-ID: <s5hehdhwiqi.wl%tiwai@suse.de>
Date:	Wed, 08 May 2013 18:15:33 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 2/3] firmware: Avoid deadlock of usermodehelper lock at shutdown

At Wed, 8 May 2013 23:56:51 +0800,
Ming Lei wrote:
> 
> On Wed, May 8, 2013 at 2:56 PM, Takashi Iwai <tiwai@...e.de> wrote:
> > When a system goes to reboot/shutdown, it tries to disable the
> > usermode helper via usermodehelper_disable().  This might be blocked
> > when a driver tries to load a firmware beforehand and it's stuck by
> > some reason.
> 
> IMO, it is better to find why the loading is stuck. Also we already provides
> the timeout sysfs file to help to deal with the situation.

The loading is done manually in the case of dell_rbu driver, so it may
happen at any time that the f/w loading doesn't finish properly.


> > In this patch, the firmware class driver registers a reboot notifier
> > so that it can abort all pending f/w bufs.  Also enable a flag for
> > avoiding the call of usermodehelper after the reboot/shutdown starts.
> 
> With this patch, maybe we only hide the real problem.

No, you can simulate the hang easily.  Try the below (you can run it
on every x86 machine; it just loads the data onto the memory.)

- modprobe dell_rbu

- echo init > /sys/devices/platform/dell_rbu/image_type

  (... now /sys/class/firmware/dell_rbu/* appear)

- echo 1 > /sys/class/firmware/dell_rbu/loading

- halt -p

Now the machine gets stuck.

Yes, the real problem is obvious: you didn't finish the f/w loading in
the above, and it will never happen.  This doesn't justify that the
machine can be stalled at shutdown, though.


Takashi
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