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Subject[PATCH v2 5.10] 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 eb75efdec8dd0f01ac85c88feafa6e63b34a2521.

The above commit is reverted as the usage of tx_mutex seems not to solve
the problem described in eb75efdec8dd ("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>
Reviewed-by: Pavel Machek <pavel@denx.de>
---
v1->v2: added signed-off-by and reviewed-by

drivers/tty/n_gsm.c | 39 +++++++++++++++++++++------------------
1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index c91a3004931f..c2212f52a603 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -235,7 +235,7 @@ struct gsm_mux {
int old_c_iflag; /* termios c_iflag value before attach */
bool constipated; /* Asked by remote to shut up */

- 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
@@ -820,14 +820,15 @@ static void __gsm_data_queue(struct gsm_dlci *dlci, struct gsm_msg *msg)
*
* Add data to the transmit queue and try and get stuff moving
* out of the mux tty if not already doing so. Take the
- * the gsm tx mutex and dlci lock.
+ * the gsm tx lock and dlci lock.
*/

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);
}

/**
@@ -839,7 +840,7 @@ 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)
@@ -902,7 +903,7 @@ 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,
@@ -918,7 +919,7 @@ 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)
@@ -1018,12 +1019,13 @@ static void 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) {
@@ -1034,7 +1036,7 @@ 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);
}

/*
@@ -1256,6 +1258,7 @@ static void gsm_control_message(struct gsm_mux *gsm, unsigned int command,
const u8 *data, int clen)
{
u8 buf[1];
+ unsigned long flags;

switch (command) {
case CMD_CLD: {
@@ -1277,9 +1280,9 @@ static void gsm_control_message(struct gsm_mux *gsm, unsigned int command,
gsm->constipated = false;
gsm_control_reply(gsm, CMD_FCON, NULL, 0);
/* Kick the link in case it is idling */
- mutex_lock(&gsm->tx_mutex);
+ spin_lock_irqsave(&gsm->tx_lock, flags);
gsm_data_kick(gsm, NULL);
- mutex_unlock(&gsm->tx_mutex);
+ spin_unlock_irqrestore(&gsm->tx_lock, flags);
break;
case CMD_FCOFF:
/* Modem wants us to STFU */
@@ -2225,7 +2228,6 @@ 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);
@@ -2297,12 +2299,12 @@ 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_list);
timer_setup(&gsm->t2_timer, gsm_control_retransmit, 0);
init_waitqueue_head(&gsm->event);
spin_lock_init(&gsm->control_lock);
+ spin_lock_init(&gsm->tx_lock);

gsm->t1 = T1;
gsm->t2 = T2;
@@ -2327,7 +2329,6 @@ 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);
@@ -2652,15 +2653,16 @@ static int gsmld_open(struct tty_struct *tty)
static void gsmld_write_wakeup(struct tty_struct *tty)
{
struct gsm_mux *gsm = tty->disc_data;
+ unsigned long flags;

/* Queue poll */
clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
- mutex_lock(&gsm->tx_mutex);
+ spin_lock_irqsave(&gsm->tx_lock, flags);
gsm_data_kick(gsm, NULL);
if (gsm->tx_bytes < TX_THRESH_LO) {
gsm_dlci_data_sweep(gsm);
}
- mutex_unlock(&gsm->tx_mutex);
+ spin_unlock_irqrestore(&gsm->tx_lock, flags);
}

/**
@@ -2703,6 +2705,7 @@ 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;

@@ -2710,13 +2713,13 @@ 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;
}
--
2.38.1
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