linux-kernel - Re: mutex_lock_slowpath warning using mxser tty driver (input/output error)

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Date:	Thu, 2 Apr 2009 23:55:08 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Christophe Lermytte <christophe.lermytte@...mson.net>,
	linux-kernel@...r.kernel.org
Subject: Re: mutex_lock_slowpath warning using mxser tty driver
 (input/output error)

On Thu, 02 Apr 2009 22:23:57 +0200
Jiri Slaby <jirislaby@...il.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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