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

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Date:   Wed, 5 Dec 2018 17:40:32 +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 08:06:21AM +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.

> 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?
Dunno, udev is beyond me.

-- 
Ville Syrjälä
Intel