linux-kernel - Re: [PATCH 1/3] Char: mxser

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Date:	Fri, 20 Apr 2007 13:12:10 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>,
	Jan "Yenya" Kasprzak <kas@...muni.cz>
Subject: Re: [PATCH 1/3] Char: mxser_new, fix recursive locking

> 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
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