linux-kernel - Re: [PATCH] Revert "tty: fix NULL pointer issue when tty

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Date:   Wed, 3 Apr 2019 10:26:58 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Johan Hovold <johan@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        linux-kernel@...r.kernel.org,
        Fabien Dessenne <fabien.dessenne@...com>
Subject: Re: [PATCH] Revert "tty: fix NULL pointer issue when tty_port ops is
 not set"

On Wed, Apr 03, 2019 at 10:06:49AM +0200, Greg Kroah-Hartman wrote:
> On Wed, Apr 03, 2019 at 09:40:53AM +0200, Johan Hovold wrote:
> > This reverts commit f4e68d58cf2b20a581759bbc7228052534652673.
> > 
> > TTY drivers using the tty-port abstraction all provide a pointer to a
> > set of port operations, which specifically cannot be NULL (or we'd find
> > out at first attempt to open a port).
> > 
> > Revert the recent commit which added unnecessary NULL-checks and whose
> > commit message indicated that it was fixing a real problem, which it did
> > not.
> > 
> > Note that even the two tty drivers for virtual devices currently
> > providing an empty set of operations probably should be implementing at
> > least some of the callbacks.
> 
> This was a "future fix" for a driver that is under review for 5.2, see
> the email thread:
> 	Subject: [PATCH 0/2] TTY: add rpmsg tty driver
>
> It didn't want/need the port pointer, if that is incorrect, that's fine,
> I'll gladly revert this, but as-is this patch isn't hurting anything,
> right?

No, it only adds the unnecessary NULL checks and some confusion by
claiming to "fix an issue".

The rpmsg tty driver not having to do anything at activate/shutdown
(first open, final close) looks a bit suspicious, but in any case I
think it's the outliers that should continue providing an empty set of
callbacks instead of sprinkling conditionals in core.

Johan