linux-kernel - Re: [PATCH v3 0/6] hid: Introduce device groups

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Message-ID: <20120430115302.GA2847@polaris.bitmath.org>
Date:	Mon, 30 Apr 2012 13:53:02 +0200
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/6] hid: Introduce device groups

Hi Jiri,

> > Just got the stacktrace on [1] though when running kernel with this 
> > patchset. The trace popped during shutdown, and the machine froze 
> > completely; I didn't have any kind of external console connected, so 
> > unfortunately I don't have the beginning of the whole thing.
> > 
> > I haven't been able to reproduce it so far. This was after several 
> > "parallel" plug/remove cycles of multiple HID devices driven by multiple 
> > different drivers.
> > 
> > I haven't performed any analysis what this might be yet.
> > 
> > [1] http://www.jikos.cz/jikos/junk/autoloading-trace.jpg
> 
> It actually seems to be spinlock lockup (due to the NMI trigger being 
> apparent at the very first line) on kbd_event_lock ...

Ah, yes. I take it you are talking about tty/vt/keyboard.c. So some
random keypress during shutdown triggers the event, which eventually
reaches input_pass_event(). From there on, the trace stays in the
mentioned driver. First kbd_event() gets called, which takes the lock
and goes on to, in turn, call kbd_keycode(), k_handler[2]() ==
k_spec(), fn_handler[9]() == fn_hold(), which goes on to call
stop_tty(). This function comes back to the driver, via con_stop(), as
vt_kbd_con_stop(), which in turn takes the same lock. So unless the
teardown of something in hid affects the choices made in the tty
driver, it appears this is a different problem. Or?

Henrik
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