linux-kernel - Re: [PATCH] TTY: Fix loss of echoed characters (2nd follow-on PATCH attached)

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Date:	Tue, 09 Sep 2008 07:15:12 -0600
From:	Joe Peterson <joe@...rush.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] TTY: Fix loss of echoed characters (2nd follow-on PATCH
 attached)

Alan Cox wrote:
> If you have the column handling isolated and locked that is a big step
> towards exterminating the BKL in the n_tty code. It also illustrates why
> locking people always say "lock data not code".

Well, it's isolated, but still locked with the BKL, which would be great
to get rid of.  A few questions for you, since you've worked with this
code (and kernel locking stuff) a lot longer than I:

1) Now that column state is confined to the process_out/echo funcs in
n_tty, would using tty_write_lock() (the defined atomic write lock
mutex) be a good replacement for lock_kernel(), even though interruptible?

2) To protect echo buffer operations, I would lean toward using a
separate echo lock mutex so it does not lock against non-echo-buffer
output.  Would nesting this with #1 be advisable?  Should it be
interruptable?

3) tty_write() mentions refers to ldisc use of the BKL.  If we change
this, are there any considerations for the tty_io or driver code?

					Thanks, Joe
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