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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Daniel Starke <daniel.starke@siemens.com>
Subject: [PATCH 5.17 210/225] tty: n_gsm: fix wrong DLCI release order
Date:   Wed,  4 May 2022 18:47:28 +0200
Message-Id: <20220504153128.764677969@linuxfoundation.org>
In-Reply-To: <20220504153110.096069935@linuxfoundation.org>
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From: Daniel Starke <daniel.starke@siemens.com>

commit deefc58bafb4841df7f0a0d85d89a1c819db9743 upstream.

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>
---
 drivers/tty/n_gsm.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2146,8 +2146,8 @@ static void gsm_cleanup_mux(struct gsm_m
 	/* 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);