Re: [PATCH AUTOSEL 6.4 24/25] usb: cdc-acm: move ldisc dcd notification outside of acm's read lock

Johan Hovold
2023-09-11T21:20:29Z

On Fri, Sep 08, 2023 at 08:37:12PM -0400, Sasha Levin wrote:
> From: Dan Drown <dan-netdev@drown.org>
>
> [ Upstream commit f72ae60881ff685004d7de7152517607fcd9968f ]
>
> dcd_change notification call moved outside of the acm->read_lock
> to protect any future tty ldisc that calls wait_serial_change()
>
> Signed-off-by: Dan Drown <dan-netdev@drown.org>
> Acked-by: Oliver Neukum <oneukum@suse.com>
> Link: https://lore.kernel.org/r/ZN1zV/zjPgpGlHXo@vps3.drown.org
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> drivers/usb/class/cdc-acm.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
> index 11da5fb284d0a..ca51230f44409 100644
> --- a/drivers/usb/class/cdc-acm.c
> +++ b/drivers/usb/class/cdc-acm.c
> @@ -318,6 +318,16 @@ static void acm_process_notification(struct acm *acm, unsigned char *buf)
> }
>
> difference = acm->ctrlin ^ newctrl;
> +
> + if ((difference & USB_CDC_SERIAL_STATE_DCD) && acm->port.tty) {
> + struct tty_ldisc *ld = tty_ldisc_ref(acm->port.tty);
> + if (ld) {
> + if (ld->ops->dcd_change)
> + ld->ops->dcd_change(acm->port.tty, newctrl & USB_CDC_SERIAL_STATE_DCD);
> + tty_ldisc_deref(ld);
> + }
> + }
> +
> spin_lock_irqsave(&acm->read_lock, flags);
> acm->ctrlin = newctrl;
> acm->oldcount = acm->iocount;

This is a fix for a commit in 6.6-rc1 (3b563b901eef ("usb: cdc-acm: add
PPS support")) so a backport of it makes no sense.

Please drop.

Johan