The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From deefc58bafb4841df7f0a0d85d89a1c819db9743 Mon Sep 17 00:00:00 2001 From: Daniel Starke daniel.starke@siemens.com Date: Thu, 14 Apr 2022 02:42:14 -0700 Subject: [PATCH] tty: n_gsm: fix wrong DLCI release order

The current DLCI release order starts with the control channel followed by the user channels. Reverse this order to keep the control channel open until all user channels have been released.

Fixes: e1eaea46bb40 ("tty: n_gsm line discipline") Cc: stable@vger.kernel.org Signed-off-by: Daniel Starke daniel.starke@siemens.com Link: https://lore.kernel.org/r/20220414094225.4527-9-daniel.starke@siemens.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index cc90b03ce005..6b953dfbb155 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -2146,8 +2146,8 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm, bool disc) /* Finish outstanding timers, making sure they are done */ del_timer_sync(&gsm->t2_timer);

- /* Free up any link layer users */ - for (i = 0; i < NUM_DLCI; i++) + /* Free up any link layer users and finally the control channel */ + for (i = NUM_DLCI - 1; i >= 0; i--) if (gsm->dlci[i]) gsm_dlci_release(gsm->dlci[i]); mutex_unlock(&gsm->mutex);