[3.19.y-ckt stable] Patch "TTY: n_gsm, fix false positive WARN_ON" has been added to the 3.19.y-ckt tree

Kamal Mostafa kamal at canonical.com
Wed Jul 6 21:00:18 UTC 2016

This is a note to let you know that I have just added a patch titled

    TTY: n_gsm, fix false positive WARN_ON

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:


This patch is scheduled to be released in version 3.19.8-ckt23.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see



>From 573629f01dafe5f48ff7984a98aafcb175fb9096 Mon Sep 17 00:00:00 2001
From: Jiri Slaby <jslaby at suse.cz>
Date: Tue, 22 Mar 2016 18:09:51 +0100
Subject: TTY: n_gsm, fix false positive WARN_ON

commit d175feca89a1c162f60f4e3560ca7bc9437c65eb upstream.

Dmitry reported, that the current cleanup code in n_gsm can trigger a
WARNING: CPU: 2 PID: 24238 at drivers/tty/n_gsm.c:2048 gsm_cleanup_mux+0x166/0x6b0()
Call Trace:
 [<ffffffff81247ab9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:490
 [<ffffffff828d0456>] gsm_cleanup_mux+0x166/0x6b0 drivers/tty/n_gsm.c:2048
 [<ffffffff828d4d87>] gsmld_open+0x5b7/0x7a0 drivers/tty/n_gsm.c:2386
 [<ffffffff828b9078>] tty_ldisc_open.isra.2+0x78/0xd0 drivers/tty/tty_ldisc.c:447
 [<ffffffff828b973a>] tty_set_ldisc+0x1ca/0xa70 drivers/tty/tty_ldisc.c:567
 [<     inline     >] tiocsetd drivers/tty/tty_io.c:2650
 [<ffffffff828a14ea>] tty_ioctl+0xb2a/0x2140 drivers/tty/tty_io.c:2883

But this is a legal path when open fails to find a space in the
gsm_mux array and tries to clean up. So make it a standard test
instead of a warning.

Reported-by: "Dmitry Vyukov" <dvyukov at google.com>
Cc: Alan Cox <alan at linux.intel.com>
Link: http://lkml.kernel.org/r/CACT4Y+bHQbAB68VFi7Romcs-Z9ZW3kQRvcq+BvHH1oa5NcAdLA@mail.gmail.com
Fixes: 5a640967 ("tty/n_gsm.c: fix a memory leak in gsmld_open()")
Signed-off-by: Jiri Slaby <jslaby at suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 drivers/tty/n_gsm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index bce16e4..db37ee4 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2045,7 +2045,9 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm)
-	WARN_ON(i == MAX_MUX);
+	/* open failed before registering => nothing to do */
+	if (i == MAX_MUX)
+		return;

 	/* In theory disconnecting DLCI 0 is sufficient but for some
 	   modems this is apparently not the case. */

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