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    Subject[PATCH 5.15 586/779] tty: n_gsm: fix missing timer to handle stalled links
    Date
    From: Daniel Starke <daniel.starke@siemens.com>

    [ Upstream commit c568f7086c6e771c77aad13d727c70ef70e07243 ]

    The current implementation does not handle the situation that no data is in
    the internal queue and needs to be sent out while the user tty fifo is
    full.
    Add a timer that moves more data from user tty down to the internal queue
    which is then serialized on the ldisc. This timer is triggered if no data
    was moved from a user tty to the internal queue within 10 * T1.

    Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
    Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
    Link: https://lore.kernel.org/r/20220701061652.39604-4-daniel.starke@siemens.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/tty/n_gsm.c | 43 +++++++++++++++++++++++++++++++++++--------
    1 file changed, 35 insertions(+), 8 deletions(-)

    diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
    index a554c22e0ee2..271efa7ae793 100644
    --- a/drivers/tty/n_gsm.c
    +++ b/drivers/tty/n_gsm.c
    @@ -244,6 +244,7 @@ struct gsm_mux {
    struct list_head tx_list; /* Pending data packets */

    /* Control messages */
    + struct timer_list kick_timer; /* Kick TX queuing on timeout */
    struct timer_list t2_timer; /* Retransmit timer for commands */
    int cretries; /* Command retry counter */
    struct gsm_control *pending_cmd;/* Our current pending command */
    @@ -850,6 +851,7 @@ static void __gsm_data_queue(struct gsm_dlci *dlci, struct gsm_msg *msg)
    list_add_tail(&msg->list, &gsm->tx_list);
    gsm->tx_bytes += msg->len;
    gsm_data_kick(gsm, dlci);
    + mod_timer(&gsm->kick_timer, jiffies + 10 * gsm->t1 * HZ / 100);
    }

    /**
    @@ -902,9 +904,6 @@ static int gsm_dlci_data_output(struct gsm_mux *gsm, struct gsm_dlci *dlci)
    size = len + h;

    msg = gsm_data_alloc(gsm, dlci->addr, size, gsm->ftype);
    - /* FIXME: need a timer or something to kick this so it can't
    - * get stuck with no work outstanding and no buffer free
    - */
    if (!msg)
    return -ENOMEM;
    dp = msg->data;
    @@ -981,9 +980,6 @@ static int gsm_dlci_data_output_framed(struct gsm_mux *gsm,

    size = len + overhead;
    msg = gsm_data_alloc(gsm, dlci->addr, size, gsm->ftype);
    -
    - /* FIXME: need a timer or something to kick this so it can't
    - get stuck with no work outstanding and no buffer free */
    if (msg == NULL) {
    skb_queue_tail(&dlci->skb_list, dlci->skb);
    dlci->skb = NULL;
    @@ -1079,9 +1075,9 @@ static int gsm_dlci_modem_output(struct gsm_mux *gsm, struct gsm_dlci *dlci,
    * renegotiate DLCI priorities with optional stuff. Needs optimising.
    */

    -static void gsm_dlci_data_sweep(struct gsm_mux *gsm)
    +static int gsm_dlci_data_sweep(struct gsm_mux *gsm)
    {
    - int len;
    + int len, ret = 0;
    /* Priority ordering: We should do priority with RR of the groups */
    int i = 1;

    @@ -1104,7 +1100,11 @@ static void gsm_dlci_data_sweep(struct gsm_mux *gsm)
    /* DLCI empty - try the next */
    if (len == 0)
    i++;
    + else
    + ret++;
    }
    +
    + return ret;
    }

    /**
    @@ -1837,6 +1837,30 @@ static void gsm_dlci_command(struct gsm_dlci *dlci, const u8 *data, int len)
    }
    }

    +/**
    + * gsm_kick_timer - transmit if possible
    + * @t: timer contained in our gsm object
    + *
    + * Transmit data from DLCIs if the queue is empty. We can't rely on
    + * a tty wakeup except when we filled the pipe so we need to fire off
    + * new data ourselves in other cases.
    + */
    +static void gsm_kick_timer(struct timer_list *t)
    +{
    + struct gsm_mux *gsm = from_timer(gsm, t, kick_timer);
    + unsigned long flags;
    + int sent = 0;
    +
    + spin_lock_irqsave(&gsm->tx_lock, flags);
    + /* If we have nothing running then we need to fire up */
    + if (gsm->tx_bytes < TX_THRESH_LO)
    + sent = gsm_dlci_data_sweep(gsm);
    + spin_unlock_irqrestore(&gsm->tx_lock, flags);
    +
    + if (sent && debug & 4)
    + pr_info("%s TX queue stalled\n", __func__);
    +}
    +
    /*
    * Allocate/Free DLCI channels
    */
    @@ -2326,6 +2350,7 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm, bool disc)
    }

    /* Finish outstanding timers, making sure they are done */
    + del_timer_sync(&gsm->kick_timer);
    del_timer_sync(&gsm->t2_timer);

    /* Free up any link layer users and finally the control channel */
    @@ -2358,6 +2383,7 @@ static int gsm_activate_mux(struct gsm_mux *gsm)
    struct gsm_dlci *dlci;
    int ret;

    + timer_setup(&gsm->kick_timer, gsm_kick_timer, 0);
    timer_setup(&gsm->t2_timer, gsm_control_retransmit, 0);
    init_waitqueue_head(&gsm->event);
    spin_lock_init(&gsm->control_lock);
    @@ -2762,6 +2788,7 @@ static int gsmld_open(struct tty_struct *tty)

    gsmld_attach_gsm(tty, gsm);

    + timer_setup(&gsm->kick_timer, gsm_kick_timer, 0);
    timer_setup(&gsm->t2_timer, gsm_control_retransmit, 0);

    return 0;
    --
    2.35.1


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