Re: [patch 0/3] Re: tty contention resulting from tty_open_by_device export

From: Okash Khawaja
Date: Mon Jul 10 2017 - 12:22:18 EST

On Mon, Jul 10, 2017 at 01:33:07PM +0100, Okash Khawaja wrote:
> > If the tty counts are being misreported then it would be better to fix
> > the code to actually manage the counts properly. The core tty code is
> > telling you that the tty is not in a valid state. While this is of
> > itself a good API to have, the underlying reference miscounting ought
> > IMHO to be fixed as well.
> When opening from kernel, we don't use file pointer. The count mismatch
> is between tty->count and #fd's. So opening from kernel leads to #fd's
> being less than tty->count. I thought this difference is relevant to
> user-space opening of tty, and not to kernel opening of tty. Can you
> suggest how to address this mismatch?
Idea is tty_kopen only ever returns a newly initialised tty - returned
by tty_init_dev. Since the access is exclusive, tty->count shouldn't
matter. When the caller is done with it, it calls tty_release_struct
which frees up the tty itself.

But yes, all the while a tty is kopened, its tty->count and #fds will be