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

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Date:	Thu, 09 May 2013 09:34:27 +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 Thu, 9 May 2013 09:19:47 +0800,
Ming Lei wrote:
> 
> On Thu, May 9, 2013 at 12:15 AM, Takashi Iwai <tiwai@...e.de> wrote:
> > 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.
> 
> OK, got it, thanks for your explanation, but anyway the stall is caused
> by not concluding the load in userspace(we have document about it),
> not by firmware loader itself.

It's the firmware loader who blocks the usermodelock :)

> I think there is no reason to disable the loading timeout for !event, could
> you test the below patch to see if it may avoid the stall?

Please test on your machine (e.g. on VM).  I'm off today for a
holiday.
As mentioned, dell_rbu can run on every machine and it's harmless.


thanks,

Takashi

> diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> index 4b1f926..caf399e 100644
> --- a/drivers/base/firmware_class.c
> +++ b/drivers/base/firmware_class.c
> @@ -848,11 +848,12 @@ static int _request_firmware_load(struct
> firmware_priv *fw_priv, bool uevent,
>  		goto err_del_bin_attr;
>  	}
> 
> +	if (timeout != MAX_SCHEDULE_TIMEOUT)
> +		schedule_delayed_work(&fw_priv->timeout_work, timeout);
> +
>  	if (uevent) {
>  		dev_set_uevent_suppress(f_dev, false);
>  		dev_dbg(f_dev, "firmware: requesting %s\n", buf->fw_id);
> -		if (timeout != MAX_SCHEDULE_TIMEOUT)
> -			schedule_delayed_work(&fw_priv->timeout_work, timeout);
> 
>  		kobject_uevent(&fw_priv->dev.kobj, KOBJ_ADD);
>  	}
> 
> 
> Thanks,
> --
> Ming Lei
> 
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