Re: [PATCH 1/1] tty: n_gsm: Avoid sleeping during .write() whilst atomic

Lee Jones
2023-10-05T16:18:00Z

On Thu, 05 Oct 2023, Greg Kroah-Hartman wrote:

> On Thu, Oct 05, 2023 at 12:46:32PM +0100, Lee Jones wrote:
> > On Thu, 05 Oct 2023, Starke, Daniel wrote:
> >
> > > > > Would something like this tick that box?
> > > > >
> > > > > diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index
> > > > > 1f3aba607cd51..5c1d2fcd5d9e2 100644
> > > > > --- a/drivers/tty/n_gsm.c
> > > > > +++ b/drivers/tty/n_gsm.c
> > > > > @@ -3716,6 +3716,10 @@ static ssize_t gsmld_write(struct tty_struct *tty, struct file *file,
> > > > > if (!gsm)
> > > > > return -ENODEV;
> > > > >
> > > > > + /* The GSM line discipline does not support binding to console */
> > > > > + if (strncmp(tty->name, "tty", 3))
> > > > > + return -EINVAL;
> > > >
> > > > No, that's not going to work, some consoles do not start with "tty" :(
> >
> > Ah, you mean there are others that we need to consider?
> >
> > I was just covering off con_write() from drivers/tty/vt/vt.c.
> >
> > Does anyone have a counter proposal?
>
> consoles are dynamically assigned, the device knows if it is a console
> or not, so there is a way to determine this at runtime. It's not a
> device naming thing at all.

It's not a device naming thing, but it is a ... :)

Okay, here's another uninformed stab in the dark:

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 1f3aba607cd51..ddf00f6a4141d 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -3629,6 +3629,10 @@ static int gsmld_open(struct tty_struct *tty)
if (tty->ops->write == NULL)
return -EINVAL;

+ /* The GSM line discipline does not support binding to console */
+ if (tty->driver->type == TTY_DRIVER_TYPE_CONSOLE)
+ return -EINVAL;
+
/* Attach our ldisc data */
gsm = gsm_alloc_mux();
if (gsm == NULL)

This seems to allow for the real serial devices (TTY_DRIVER_TYPE_SERIAL)
suggested by Daniel.

--
Lee Jones [李琼斯]