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Date: Fri, 20 Apr 2007 13:12:10 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Jiri Slaby <jirislaby@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, <linux-kernel@vger.kernel.org>,
       Jan "Yenya" Kasprzak <kas@fi.muni.cz>
Subject: Re: [PATCH 1/3] Char: mxser_new, fix recursive locking
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> Acquire a port lock only if not in_interrupt in some places, because ISR
> holds the lock yet (and ldisc calls some of driver's routines which tries to
> acquire it again due to tty->low_latency).

NAK

This is the wrong way to do it. If you don't support recursive entry then
don't use ->low_latency. If you do then ensure you drop the lock before
you call tty_flip_buffer_push().

The other way this could be tackled which has some merit is to require
that line discipline responses coming from a received frame call a new
tty method so drivers can tell callbacks from arriving data apart from
other events.

Alan