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

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Message-ID: <ZP7bkRc-1U8-M6X1@hovoldconsulting.com>
Date:   Mon, 11 Sep 2023 11:19:13 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Dan Drown <dan-netdev@...wn.org>,
        Oliver Neukum <oneukum@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 6.4 24/25] usb: cdc-acm: move ldisc dcd
 notification outside of acm's read lock

On Fri, Sep 08, 2023 at 08:37:12PM -0400, Sasha Levin wrote:
> From: Dan Drown <dan-netdev@...wn.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@...wn.org>
> Acked-by: Oliver Neukum <oneukum@...e.com>
> Link: https://lore.kernel.org/r/ZN1zV/zjPgpGlHXo@vps3.drown.org
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Sasha Levin <sashal@...nel.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