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

[Joe Peterson <joe@skyrush.com>]

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