Re: [PATCH v2 BlueZ] hid2hci: Fix udev rules for linux-4.14+ - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: linux-bluetooth@vger.kernel.org,
	"Dmitry Torokhov" <dmitry.torokhov@gmail.com>,
	"Marcel Holtmann" <marcel@holtmann.org>,
	"Kay Sievers" <kay.sievers@vrfy.org>,
	"Zbigniew Jędrzejewski-Szmek" <zbyszek@in.waw.pl>,
	systemd-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 BlueZ] hid2hci: Fix udev rules for linux-4.14+
Date: Wed, 5 Dec 2018 20:49:16 +0100	[thread overview]
Message-ID: <20181205194916.GA20809@kroah.com> (raw)
In-Reply-To: <20181205194051.GU9144@intel.com>

On Wed, Dec 05, 2018 at 09:40:51PM +0200, Ville Syrjälä wrote:
> On Wed, Dec 05, 2018 at 08:20:36PM +0100, Greg Kroah-Hartman wrote:
> > On Wed, Dec 05, 2018 at 05:40:32PM +0200, Ville Syrjälä wrote:
> > > On Wed, Dec 05, 2018 at 08:06:21AM +0100, Greg Kroah-Hartman wrote:
> > > > On Tue, Dec 04, 2018 at 10:41:17PM +0200, Ville Syrjala wrote:
> > > > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > > 
> > > > > Since commit 1455cf8dbfd0 ("driver core: emit uevents when
> > > > > device is bound to a driver") the kernel started emitting
> > > > > "bind" and "unbind" uevents which confuse the hid2hci
> > > > > udev rules.
> > > > > 
> > > > > The symptoms on an affected machine (Dell E5400 in my case)
> > > > > include bluetooth devices not appearing and udev hogging
> > > > > the cpu as it's busy processing a constant stream of these
> > > > > "bind"+"unbind" uevents.
> > > > 
> > > > What is causing a "stream" of bind and unbind events?  This only happens
> > > > when a device is attached to a driver or removed from a driver, which is
> > > > caused by something else happening.
> > > 
> > > Not sure if it's just due to this thing causing devices to
> > > appear/disappear during bind/unbind events or what.
> > 
> > Someone has to be telling the kernel to bind/unbind from a driver to
> > a device, it doesn't do it on its own.  Look at your other rules/scripts
> > for that.
> > 
> > Also note that the kernel has been doing this for over a year now (since
> > 4.l4), what just happened in 4.19 to cause this to be an issue?
> 
> It became an issue for me after I got a machine that suffers from
> this. The regression has been present ever since commit 1455cf8dbfd0
> ("driver core: emit uevents when device is bound to a driver").
> 
> You need a Dell E5400 or something similar to see it since those
> have these magic bluetooth devices or whatever.

What does the kernel log say is going on?  Is the device "bouncing" from
being added/removed from the system all the time?

What makes this system "magic"?

> > > > This should not be a normal
> > > > occurance, unless something odd is happening to your hardware?
> > > 
> > > It's not specific to my hardware. Lot's of people are affected.
> > > See eg. 
> > > https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1759836
> > > 
> > > Acutally looking through that bug it seems someone else noticed
> > > hid2hci failing lot in the logs. So maybe it's just that we already
> > > switched the mode during "add", and then we try to redo the same
> > > thing during "bind" which fails, and that then causes and unbind?
> > 
> > You have to manually unbind the device, the kernel does not do that.  So
> > perhaps you have a broken udev rule somewhere else that would do
> > something odd like unbind/bind?
> > 
> > I don't see this happening on my systems, but hey, I know better than to
> > run Ubuntu :)
> 
> As do I. And you don't see it because you don't have the right
> hardware.

Fair enough, what makes my hardware different from yours?

thanks,

greg k-h