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    Subject[PATCH AUTOSEL 6.0 10/44] Revert "tty: n_gsm: avoid call of sleeping functions from atomic context"
    Date
    From: Fedor Pchelkin <pchelkin@ispras.ru>

    [ Upstream commit acdab4cb4ba7e5f94d2b422ebd7bf4bf68178fb2 ]

    This reverts commit 902e02ea9385373ce4b142576eef41c642703955.

    The above commit is reverted as the usage of tx_mutex seems not to solve
    the problem described in 902e02ea9385 ("tty: n_gsm: avoid call of sleeping
    functions from atomic context") and just moves the bug to another place.

    Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
    Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
    Reviewed-by: Daniel Starke <daniel.starke@siemens.com>
    Link: https://lore.kernel.org/r/20221008110221.13645-2-pchelkin@ispras.ru
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/tty/n_gsm.c | 53 +++++++++++++++++++++++++--------------------
    1 file changed, 29 insertions(+), 24 deletions(-)

    diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
    index 01c112e2e214..e23225aff5d9 100644
    --- a/drivers/tty/n_gsm.c
    +++ b/drivers/tty/n_gsm.c
    @@ -248,7 +248,7 @@ struct gsm_mux {
    bool constipated; /* Asked by remote to shut up */
    bool has_devices; /* Devices were registered */

    - struct mutex tx_mutex;
    + spinlock_t tx_lock;
    unsigned int tx_bytes; /* TX data outstanding */
    #define TX_THRESH_HI 8192
    #define TX_THRESH_LO 2048
    @@ -680,6 +680,7 @@ static int gsm_send(struct gsm_mux *gsm, int addr, int cr, int control)
    struct gsm_msg *msg;
    u8 *dp;
    int ocr;
    + unsigned long flags;

    msg = gsm_data_alloc(gsm, addr, 0, control);
    if (!msg)
    @@ -701,10 +702,10 @@ static int gsm_send(struct gsm_mux *gsm, int addr, int cr, int control)

    gsm_print_packet("Q->", addr, cr, control, NULL, 0);

    - mutex_lock(&gsm->tx_mutex);
    + spin_lock_irqsave(&gsm->tx_lock, flags);
    list_add_tail(&msg->list, &gsm->tx_ctrl_list);
    gsm->tx_bytes += msg->len;
    - mutex_unlock(&gsm->tx_mutex);
    + spin_unlock_irqrestore(&gsm->tx_lock, flags);
    gsmld_write_trigger(gsm);

    return 0;
    @@ -729,7 +730,7 @@ static void gsm_dlci_clear_queues(struct gsm_mux *gsm, struct gsm_dlci *dlci)
    spin_unlock_irqrestore(&dlci->lock, flags);

    /* Clear data packets in MUX write queue */
    - mutex_lock(&gsm->tx_mutex);
    + spin_lock_irqsave(&gsm->tx_lock, flags);
    list_for_each_entry_safe(msg, nmsg, &gsm->tx_data_list, list) {
    if (msg->addr != addr)
    continue;
    @@ -737,7 +738,7 @@ static void gsm_dlci_clear_queues(struct gsm_mux *gsm, struct gsm_dlci *dlci)
    list_del(&msg->list);
    kfree(msg);
    }
    - mutex_unlock(&gsm->tx_mutex);
    + spin_unlock_irqrestore(&gsm->tx_lock, flags);
    }

    /**
    @@ -1023,9 +1024,10 @@ static void __gsm_data_queue(struct gsm_dlci *dlci, struct gsm_msg *msg)

    static void gsm_data_queue(struct gsm_dlci *dlci, struct gsm_msg *msg)
    {
    - mutex_lock(&dlci->gsm->tx_mutex);
    + unsigned long flags;
    + spin_lock_irqsave(&dlci->gsm->tx_lock, flags);
    __gsm_data_queue(dlci, msg);
    - mutex_unlock(&dlci->gsm->tx_mutex);
    + spin_unlock_irqrestore(&dlci->gsm->tx_lock, flags);
    }

    /**
    @@ -1037,7 +1039,7 @@ static void gsm_data_queue(struct gsm_dlci *dlci, struct gsm_msg *msg)
    * is data. Keep to the MRU of the mux. This path handles the usual tty
    * interface which is a byte stream with optional modem data.
    *
    - * Caller must hold the tx_mutex of the mux.
    + * Caller must hold the tx_lock of the mux.
    */

    static int gsm_dlci_data_output(struct gsm_mux *gsm, struct gsm_dlci *dlci)
    @@ -1097,7 +1099,7 @@ static int gsm_dlci_data_output(struct gsm_mux *gsm, struct gsm_dlci *dlci)
    * is data. Keep to the MRU of the mux. This path handles framed data
    * queued as skbuffs to the DLCI.
    *
    - * Caller must hold the tx_mutex of the mux.
    + * Caller must hold the tx_lock of the mux.
    */

    static int gsm_dlci_data_output_framed(struct gsm_mux *gsm,
    @@ -1113,7 +1115,7 @@ static int gsm_dlci_data_output_framed(struct gsm_mux *gsm,
    if (dlci->adaption == 4)
    overhead = 1;

    - /* dlci->skb is locked by tx_mutex */
    + /* dlci->skb is locked by tx_lock */
    if (dlci->skb == NULL) {
    dlci->skb = skb_dequeue_tail(&dlci->skb_list);
    if (dlci->skb == NULL)
    @@ -1167,7 +1169,7 @@ static int gsm_dlci_data_output_framed(struct gsm_mux *gsm,
    * Push an empty frame in to the transmit queue to update the modem status
    * bits and to transmit an optional break.
    *
    - * Caller must hold the tx_mutex of the mux.
    + * Caller must hold the tx_lock of the mux.
    */

    static int gsm_dlci_modem_output(struct gsm_mux *gsm, struct gsm_dlci *dlci,
    @@ -1281,12 +1283,13 @@ static int gsm_dlci_data_sweep(struct gsm_mux *gsm)

    static void gsm_dlci_data_kick(struct gsm_dlci *dlci)
    {
    + unsigned long flags;
    int sweep;

    if (dlci->constipated)
    return;

    - mutex_lock(&dlci->gsm->tx_mutex);
    + spin_lock_irqsave(&dlci->gsm->tx_lock, flags);
    /* If we have nothing running then we need to fire up */
    sweep = (dlci->gsm->tx_bytes < TX_THRESH_LO);
    if (dlci->gsm->tx_bytes == 0) {
    @@ -1297,7 +1300,7 @@ static void gsm_dlci_data_kick(struct gsm_dlci *dlci)
    }
    if (sweep)
    gsm_dlci_data_sweep(dlci->gsm);
    - mutex_unlock(&dlci->gsm->tx_mutex);
    + spin_unlock_irqrestore(&dlci->gsm->tx_lock, flags);
    }

    /*
    @@ -1991,13 +1994,14 @@ static void gsm_dlci_command(struct gsm_dlci *dlci, const u8 *data, int len)
    static void gsm_kick_timeout(struct work_struct *work)
    {
    struct gsm_mux *gsm = container_of(work, struct gsm_mux, kick_timeout.work);
    + unsigned long flags;
    int sent = 0;

    - mutex_lock(&gsm->tx_mutex);
    + 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);
    - mutex_unlock(&gsm->tx_mutex);
    + spin_unlock_irqrestore(&gsm->tx_lock, flags);

    if (sent && debug & 4)
    pr_info("%s TX queue stalled\n", __func__);
    @@ -2527,7 +2531,6 @@ static void gsm_free_mux(struct gsm_mux *gsm)
    break;
    }
    }
    - mutex_destroy(&gsm->tx_mutex);
    mutex_destroy(&gsm->mutex);
    kfree(gsm->txframe);
    kfree(gsm->buf);
    @@ -2599,7 +2602,6 @@ static struct gsm_mux *gsm_alloc_mux(void)
    }
    spin_lock_init(&gsm->lock);
    mutex_init(&gsm->mutex);
    - mutex_init(&gsm->tx_mutex);
    kref_init(&gsm->ref);
    INIT_LIST_HEAD(&gsm->tx_ctrl_list);
    INIT_LIST_HEAD(&gsm->tx_data_list);
    @@ -2608,6 +2610,7 @@ static struct gsm_mux *gsm_alloc_mux(void)
    INIT_WORK(&gsm->tx_work, gsmld_write_task);
    init_waitqueue_head(&gsm->event);
    spin_lock_init(&gsm->control_lock);
    + spin_lock_init(&gsm->tx_lock);

    gsm->t1 = T1;
    gsm->t2 = T2;
    @@ -2632,7 +2635,6 @@ static struct gsm_mux *gsm_alloc_mux(void)
    }
    spin_unlock(&gsm_mux_lock);
    if (i == MAX_MUX) {
    - mutex_destroy(&gsm->tx_mutex);
    mutex_destroy(&gsm->mutex);
    kfree(gsm->txframe);
    kfree(gsm->buf);
    @@ -2788,16 +2790,17 @@ static void gsmld_write_trigger(struct gsm_mux *gsm)
    static void gsmld_write_task(struct work_struct *work)
    {
    struct gsm_mux *gsm = container_of(work, struct gsm_mux, tx_work);
    + unsigned long flags;
    int i, ret;

    /* All outstanding control channel and control messages and one data
    * frame is sent.
    */
    ret = -ENODEV;
    - mutex_lock(&gsm->tx_mutex);
    + spin_lock_irqsave(&gsm->tx_lock, flags);
    if (gsm->tty)
    ret = gsm_data_kick(gsm);
    - mutex_unlock(&gsm->tx_mutex);
    + spin_unlock_irqrestore(&gsm->tx_lock, flags);

    if (ret >= 0)
    for (i = 0; i < NUM_DLCI; i++)
    @@ -3005,6 +3008,7 @@ static ssize_t gsmld_write(struct tty_struct *tty, struct file *file,
    const unsigned char *buf, size_t nr)
    {
    struct gsm_mux *gsm = tty->disc_data;
    + unsigned long flags;
    int space;
    int ret;

    @@ -3012,13 +3016,13 @@ static ssize_t gsmld_write(struct tty_struct *tty, struct file *file,
    return -ENODEV;

    ret = -ENOBUFS;
    - mutex_lock(&gsm->tx_mutex);
    + spin_lock_irqsave(&gsm->tx_lock, flags);
    space = tty_write_room(tty);
    if (space >= nr)
    ret = tty->ops->write(tty, buf, nr);
    else
    set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
    - mutex_unlock(&gsm->tx_mutex);
    + spin_unlock_irqrestore(&gsm->tx_lock, flags);

    return ret;
    }
    @@ -3315,13 +3319,14 @@ static struct tty_ldisc_ops tty_ldisc_packet = {
    static void gsm_modem_upd_via_data(struct gsm_dlci *dlci, u8 brk)
    {
    struct gsm_mux *gsm = dlci->gsm;
    + unsigned long flags;

    if (dlci->state != DLCI_OPEN || dlci->adaption != 2)
    return;

    - mutex_lock(&gsm->tx_mutex);
    + spin_lock_irqsave(&gsm->tx_lock, flags);
    gsm_dlci_modem_output(gsm, dlci, brk);
    - mutex_unlock(&gsm->tx_mutex);
    + spin_unlock_irqrestore(&gsm->tx_lock, flags);
    }

    /**
    --
    2.35.1
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