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

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Message-ID: <20181205194051.GU9144@intel.com>
Date:   Wed, 5 Dec 2018 21:40:51 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-bluetooth@...r.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        Kay Sievers <kay.sievers@...y.org>,
        Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>,
        systemd-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 BlueZ] hid2hci: Fix udev rules for linux-4.14+

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@...ux.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.

> 
> > > 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.

-- 
Ville Syrjälä
Intel