The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5098e77962e7c8947f87bd8c5869c83e000a522a Mon Sep 17 00:00:00 2001

From: Johan Hovold johan@kernel.org Date: Mon, 26 Oct 2020 11:43:06 +0100 Subject: [PATCH] USB: serial: digi_acceleport: fix write-wakeup deadlocks

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

diff --git a/drivers/usb/serial/digi_acceleport.c b/drivers/usb/serial/digi_acceleport.c index 016e7dec3196..968e08cdcb09 100644 --- a/drivers/usb/serial/digi_acceleport.c +++ b/drivers/usb/serial/digi_acceleport.c @@ -19,7 +19,6 @@ #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> @@ -198,14 +197,12 @@ 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, @@ -356,26 +353,6 @@ __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(struct urb *urb) unsigned long flags; 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(struct urb *urb) }

/* try to send any buffered data on this port */ + wakeup = true; spin_lock_irqsave(&priv->dp_port_lock, flags); priv->dp_write_urb_in_use = 0; if (priv->dp_out_buf_len > 0) { @@ -1026,19 +1005,18 @@ static void digi_write_bulk_callback(struct urb *urb) 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_irqrestore(&priv->dp_port_lock, flags); + 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_serial_port *port, unsigned port_num) 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); @@ -1507,13 +1484,14 @@ static int digi_read_oob_callback(struct urb *urb) rts = C_CRTSCTS(tty);

if (tty && opcode == DIGI_CMD_READ_INPUT_SIGNALS) { + bool wakeup = false; + spin_lock_irqsave(&priv->dp_port_lock, flags); /* 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 */ @@ -1532,6 +1510,9 @@ static int digi_read_oob_callback(struct urb *urb) priv->dp_modem_signals &= ~TIOCM_CD;

spin_unlock_irqrestore(&priv->dp_port_lock, flags); + + if (wakeup) + tty_port_tty_wakeup(&port->port); } else if (opcode == DIGI_CMD_TRANSMIT_IDLE) { spin_lock_irqsave(&priv->dp_port_lock, flags); priv->dp_transmit_idle = 1;