linux-kernel - Re: [PATCH] ACPI: Set flag DOCK_UNDOCKING when triggered via sysfs

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Date:	Thu, 13 Mar 2008 19:14:56 +0100
From:	Holger Macht <hmacht@...e.de>
To:	Kristen Carlson Accardi <kristen.c.accardi@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Len Brown <lenb@...nel.org>, stable@...nel.org
Subject: Re: [PATCH] ACPI: Set flag DOCK_UNDOCKING when triggered via sysfs

On Thu 13. Mar - 10:27:57, Kristen Carlson Accardi wrote:
> On Wed, 12 Mar 2008 11:40:35 +0100
> Holger Macht <hmacht@...e.de> wrote:
> 
> > On Di 11. Mär - 22:35:22, Andrew Morton wrote:
> > > On Wed, 12 Mar 2008 01:07:27 +0100 Holger Macht <hmacht@...e.de>
> > > wrote:
> > > 
> > > > begin_undock() is only called when triggered via a acpi notify
> > > > handler (pressing the undock button on the dock station), but
> > > > complete_undock() is always called after the eject. So if a
> > > > undock is triggered through a sysfs write, the flag
> > > > DOCK_UNDOCKING has to be set for the dock station, too. Otherwise
> > > > this will freeze the system hard.
> > > > 
> > > 
> > > We prefer not to make systems freeze hard.
> > > 
> > > > ---
> > > > 
> > > > diff --git a/drivers/acpi/dock.c b/drivers/acpi/dock.c
> > > > index 307cef6..fa44fb9 100644
> > > > --- a/drivers/acpi/dock.c
> > > > +++ b/drivers/acpi/dock.c
> > > > @@ -710,6 +710,7 @@ static ssize_t write_undock(struct device
> > > > *dev, struct device_attribute *attr, if (!count)
> > > >  		return -EINVAL;
> > > >  
> > > > +	begin_undock(dock_station);
> > > >  	ret = handle_eject_request(dock_station,
> > > > ACPI_NOTIFY_EJECT_REQUEST); return ret ? ret: count;
> > > >  }
> > > 
> > > I assume that this is needed in 2.6.24.x as well?
> > 
> > I tested this, and no, I weren't able to reproduce on 2.6.24.
> > 
> > Moreover, it seems that the freeze is related to some libata issue
> > because it only freezes when a drive is in the dock station.
> > 
> > Nevertheless, I think the patch is correct. Maybe there's a race
> > involved somewhere I'm not aware of. I really like to wait for
> > Kristen to comment before pushing it into more trees.
> > 
> > Thanks,
> > 	Holger
> > 
> 
> Hum, I'm surprised this caused a freeze - you are sure this fixes your
> problem?  This flag is never checked anywhere in the dock code, and if
> it's not set, it will not matter, it will still do the undock.  The
> flags file is exported to user space via sysfs though, so maybe because
> the flag isn't being set, some user space script is doing something it
> shouldn't?  The patch does seem correct though, so might as well add it.

No, now I know that it doesn't seem to be the root cause. It definitely
helps here, so it seems to be a race.

My userspace does not read the flags file and is doing something bad in
turn of it. The freeze is caused by HAL, which reads /dev/sr0 after
docking, but just before libata detaches the device. We're currently about
to fix this:

 http://lkml.org/lkml/2008/3/11/418

However, it seems that the patch is not perfect yet :-(

> Acked-by:  Kristen Carlson Accardi <kristen.c.accardi@...el.com>

Thanks,
	Holger
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