Date: Thu, 2 Apr 2009 23:55:08 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Jiri Slaby <jirislaby@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
       Christophe Lermytte <christophe.lermytte@thomson.net>,
       linux-kernel@vger.kernel.org
Subject: Re: mutex_lock_slowpath warning using mxser tty driver
 (input/output error)
Message-ID: <20090402235508.31c7f2b6@lxorguk.ukuu.org.uk>
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	<1238696349.5133.25.camel@laptop>
	<20090402194401.154bbc36@lxorguk.ukuu.org.uk>
	<49D51EDD.4060902@gmail.com>
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On Thu, 02 Apr 2009 22:23:57 +0200
Jiri Slaby <jirislaby@gmail.com> wrote:

> On 04/02/2009 08:44 PM, Alan Cox wrote:
> >> It appears to want to lock a mutex in interrupt context, something
> >> that's a definite no-no.
> >>
> >> CCed the folks who might know a thing or two about the driver.
> > 
> > Moxa is not a USB driver so the USB trace at the end makes no sense at
> > all.
> 
> Yes, unreliable stack entries, but echo_set_canon_col is called from irq
> context and locks mutex.

Which means that either the driver is calling the ldisc receive handlers
from an IRQ directly (not allowed) or calling the tty_flip_buffer_push
paths and set tty->low_latency

2.6.29 is the first kernel that catches this bug with warnings.

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