Date: Thu, 3 Feb 2005 10:21:12 -0800
From: Andrew Morton <akpm@osdl.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: rmk+lkml@arm.linux.org.uk, e9925248@student.tuwien.ac.at,
       linux-kernel@vger.kernel.org
Subject: Re: Deadlock in serial driver 2.6.x
Message-Id: <20050203102112.06c06fe7.akpm@osdl.org>
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Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
>
> On Llu, 2005-01-31 at 08:48, Andrew Morton wrote:
> > >  The tty layer cannot fix this for now, and I don't intend to fix it. Fix
> > >  the serial driver: the fix is quite simple since you can keep a field in
> > >  the driver for now to detect recursive calling into the echo case and
> > >  don't relock.
> > 
> > Are we sure that the serial driver is the only one which will hit this
> > deadlock?
> 
> Yes fairly sure. The feature has been a well known but non-documented
> property of the tty layer since about 1.0. There are two ways I see to
> clean it up - we
> can have the serial driver behave like other drivers and if need be
> known about
> recursive entries or we could extend the driver interface with an "echo"
> method used by line disciplines when calling back to the tty driver from
> a data
> receive event.

The "echo method" method sounds good.  Do we think that's feasible for
2.6.11, or would it be safer to disable low-latency mode for that driver?
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