[PATCH 4.9 10/32] USB: serial: digi_acceleport: fix write-wakeup deadlocks

Greg Kroah-Hartman
2021-01-07T14:17:18Z

From: Johan Hovold <johan@kernel.org>

[ Upstream commit 5098e77962e7c8947f87bd8c5869c83e000a522a ]

The driver must not call tty_wakeup() while holding its private lock as
line disciplines are allowed to call back into write() from
write_wakeup(), leading to a deadlock.

Also remove the unneeded work struct that was used to defer wakeup in
order to work around a possible race in ancient times (see comment about
n_tty write_chan() in commit 14b54e39b412 ("USB: serial: remove
changelogs and old todo entries")).

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/serial/digi_acceleport.c | 45 ++++++++++-------------------------
1 file changed, 13 insertions(+), 32 deletions(-)

--- a/drivers/usb/serial/digi_acceleport.c
+++ b/drivers/usb/serial/digi_acceleport.c
@@ -23,7 +23,6 @@
#include <linux/tty_flip.h>
#include <linux/module.h>
#include <linux/spinlock.h>
-#include <linux/workqueue.h>
#include <linux/uaccess.h>
#include <linux/usb.h>
#include <linux/wait.h>
@@ -201,14 +200,12 @@ struct digi_port {
int dp_throttle_restart;
wait_queue_head_t dp_flush_wait;
wait_queue_head_t dp_close_wait; /* wait queue for close */
- struct work_struct dp_wakeup_work;
struct usb_serial_port *dp_port;
};

/* Local Function Declarations */

-static void digi_wakeup_write_lock(struct work_struct *work);
static int digi_write_oob_command(struct usb_serial_port *port,
unsigned char *buf, int count, int interruptible);
static int digi_write_inb_command(struct usb_serial_port *port,
@@ -355,26 +352,6 @@ __releases(lock)
return timeout;
}

-
-/*
- * Digi Wakeup Write
- *
- * Wake up port, line discipline, and tty processes sleeping
- * on writes.
- */
-
-static void digi_wakeup_write_lock(struct work_struct *work)
-{
- struct digi_port *priv =
- container_of(work, struct digi_port, dp_wakeup_work);
- struct usb_serial_port *port = priv->dp_port;
- unsigned long flags;
-
- spin_lock_irqsave(&priv->dp_port_lock, flags);
- tty_port_tty_wakeup(&port->port);
- spin_unlock_irqrestore(&priv->dp_port_lock, flags);
-}
-
/*
* Digi Write OOB Command
*
@@ -985,6 +962,7 @@ static void digi_write_bulk_callback(str
struct digi_serial *serial_priv;
int ret = 0;
int status = urb->status;
+ bool wakeup;

/* port and serial sanity check */
if (port == NULL || (priv = usb_get_serial_port_data(port)) == NULL) {
@@ -1011,6 +989,7 @@ static void digi_write_bulk_callback(str
}

/* try to send any buffered data on this port */
+ wakeup = true;
spin_lock(&priv->dp_port_lock);
priv->dp_write_urb_in_use = 0;
if (priv->dp_out_buf_len > 0) {
@@ -1026,19 +1005,18 @@ static void digi_write_bulk_callback(str
if (ret == 0) {
priv->dp_write_urb_in_use = 1;
priv->dp_out_buf_len = 0;
+ wakeup = false;
}
}
- /* wake up processes sleeping on writes immediately */
- tty_port_tty_wakeup(&port->port);
- /* also queue up a wakeup at scheduler time, in case we */
- /* lost the race in write_chan(). */
- schedule_work(&priv->dp_wakeup_work);
-
spin_unlock(&priv->dp_port_lock);
+
if (ret && ret != -EPERM)
dev_err_console(port,
"%s: usb_submit_urb failed, ret=%d, port=%d\n",
__func__, ret, priv->dp_port_num);
+
+ if (wakeup)
+ tty_port_tty_wakeup(&port->port);
}

static int digi_write_room(struct tty_struct *tty)
@@ -1238,7 +1216,6 @@ static int digi_port_init(struct usb_ser
init_waitqueue_head(&priv->dp_transmit_idle_wait);
init_waitqueue_head(&priv->dp_flush_wait);
init_waitqueue_head(&priv->dp_close_wait);
- INIT_WORK(&priv->dp_wakeup_work, digi_wakeup_write_lock);
priv->dp_port = port;

init_waitqueue_head(&port->write_wait);
@@ -1524,13 +1501,14 @@ static int digi_read_oob_callback(struct
rts = C_CRTSCTS(tty);

if (tty && opcode == DIGI_CMD_READ_INPUT_SIGNALS) {
+ bool wakeup = false;
+
spin_lock(&priv->dp_port_lock);
/* convert from digi flags to termiox flags */
if (val & DIGI_READ_INPUT_SIGNALS_CTS) {
priv->dp_modem_signals |= TIOCM_CTS;
- /* port must be open to use tty struct */
if (rts)
- tty_port_tty_wakeup(&port->port);
+ wakeup = true;
} else {
priv->dp_modem_signals &= ~TIOCM_CTS;
/* port must be open to use tty struct */
@@ -1549,6 +1527,9 @@ static int digi_read_oob_callback(struct
priv->dp_modem_signals &= ~TIOCM_CD;

spin_unlock(&priv->dp_port_lock);
+
+ if (wakeup)
+ tty_port_tty_wakeup(&port->port);
} else if (opcode == DIGI_CMD_TRANSMIT_IDLE) {
spin_lock(&priv->dp_port_lock);
priv->dp_transmit_idle = 1;