patch "TTY: n_gsm, fix false positive WARN_ON" added to tty-next

patch "TTY: n_gsm, fix false positive WARN_ON" added to tty-next

[gregkh]

This is a note to let you know that I've just added the patch titled

    TTY: n_gsm, fix false positive WARN_ON

to my tty git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-next branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release
during the merge window.

If you have any questions about this process, please let me know.


>From d175feca89a1c162f60f4e3560ca7bc9437c65eb Mon Sep 17 00:00:00 2001
From: Jiri Slaby <jslaby@suse.cz>
Date: Tue, 22 Mar 2016 18:09:51 +0100
Subject: TTY: n_gsm, fix false positive WARN_ON

Dmitry reported, that the current cleanup code in n_gsm can trigger a
warning:
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@google.com>
Cc: Alan Cox <alan@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()")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 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 c01620780f5b..365dfd8bc42b 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)
 		}
 	}
 	spin_unlock(&gsm_mux_lock);
-	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. */
-- 
2.8.0