Subject: Re: The Serial Layer
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: arjanv@redhat.com,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Iau, 2004-09-09 at 13:57, Theodore Ts'o wrote:
> Calling ldisc.receive_buf directly() should be OK as long as you're
> not in an interrupt handler.  (For example the comtrol driver polls in
> a timer bottom-half, so it's OK to call ldisc.receive_buf).
> Unfortunately, some drivers don't quite follow the rules.

If the driver calls ldisc->receive_buf it means it bypasses the
TTY_DONT_FLIP locking used by the n_tty driver. Am I missing something
here.

> The hangup handling needs to be completely redone, so that we don't
> force serial drivers to do a completely shutdown of the port in an
> interrupt context.  If the drivers are careful, it can be safe, but
> it's too hard to handle hangup correctly.  

Most of that I think comes out in the wash with the ldisc locking. 
Once the driver uses tty_ldisc_ref() it'll get NULL back in the case
where the hangup raced the driver. I'm also no longer dropping back
to N_TTY in the hangup path. I couldn't see any reason this was
neccessary since the release will clean it up anyway ?

Alan

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