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

From: Joe Peterson
Date: Tue Sep 09 2008 - 09:15:26 EST

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

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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