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    Subject[PATCH 4.5 64/87] TTY: n_gsm, fix false positive WARN_ON
    Date
    4.5-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jiri Slaby <jslaby@suse.cz>

    commit d175feca89a1c162f60f4e3560ca7bc9437c65eb upstream.

    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()")
    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(-)

    --- a/drivers/tty/n_gsm.c
    +++ b/drivers/tty/n_gsm.c
    @@ -2045,7 +2045,9 @@ static void gsm_cleanup_mux(struct gsm_m
    }
    }
    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. */

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