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    Subject[PATCH v2 RESEND] tty/n_gsm.c: fix a memory leak when gsmtty is removed
    when gsmtty_remove put dlci, it will cause memory leak if dlci->port's refcount is zero.
    So we do the cleanup work in .cleanup callback instead.

    dlci will be last put in two call chains.
    1) gsmld_close -> gsm_cleanup_mux -> gsm_dlci_release -> dlci_put
    2) gsmld_remove -> dlci_put
    so there is a race. the memory leak depends on the race.

    In call chain 2. we hit the memory leak. below comment tells.

    release_tty -> tty_driver_remove_tty -> gsmtty_remove -> dlci_put -> tty_port_destructor (WARN_ON(port->itty) and return directly)
    |
    tty->port->itty = NULL;
    |
    tty_kref_put ---> release_one_tty -> gsmtty_cleanup (added by our patch)

    So our patch fix the memory leak by doing the cleanup work after tty core did.

    Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>
    ---
    Changes in v2:
    Don't use schedule_work to put dlci. Replace .remove with .cleanup callback.

    drivers/tty/n_gsm.c | 5 ++---
    1 file changed, 2 insertions(+), 3 deletions(-)

    diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
    index c434376..bce16e4 100644
    --- a/drivers/tty/n_gsm.c
    +++ b/drivers/tty/n_gsm.c
    @@ -3170,7 +3170,7 @@ static int gsmtty_break_ctl(struct tty_struct *tty, int state)
    return gsmtty_modem_update(dlci, encode);
    }

    -static void gsmtty_remove(struct tty_driver *driver, struct tty_struct *tty)
    +static void gsmtty_cleanup(struct tty_struct *tty)
    {
    struct gsm_dlci *dlci = tty->driver_data;
    struct gsm_mux *gsm = dlci->gsm;
    @@ -3178,7 +3178,6 @@ static void gsmtty_remove(struct tty_driver *driver, struct tty_struct *tty)
    dlci_put(dlci);
    dlci_put(gsm->dlci[0]);
    mux_put(gsm);
    - driver->ttys[tty->index] = NULL;
    }

    /* Virtual ttys for the demux */
    @@ -3199,7 +3198,7 @@ static const struct tty_operations gsmtty_ops = {
    .tiocmget = gsmtty_tiocmget,
    .tiocmset = gsmtty_tiocmset,
    .break_ctl = gsmtty_break_ctl,
    - .remove = gsmtty_remove,
    + .cleanup = gsmtty_cleanup,
    };


    --
    1.9.1

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