[PATCH 3.15 036/109] slcan: Port write_wakeup deadlock fix from slip

Greg Kroah-Hartman
2014-07-26T19:19:50Z

From: Tyler Hall <tylerwhall@gmail.com>

[ Upstream commit a8e83b17536aad603fbeae4c460f2da0ee9fe6ed ]

The commit "slip: Fix deadlock in write_wakeup" fixes a deadlock caused
by a change made in both slcan and slip. This is a direct port of that
fix.

Signed-off-by: Tyler Hall <tylerwhall@gmail.com>
Cc: Oliver Hartkopp <socketcan@hartkopp.net>
Cc: Andre Naujoks <nautsch2@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/can/slcan.c | 37 +++++++++++++++++++++++++++----------
1 file changed, 27 insertions(+), 10 deletions(-)

--- a/drivers/net/can/slcan.c
+++ b/drivers/net/can/slcan.c
@@ -52,6 +52,7 @@
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/kernel.h>
+#include <linux/workqueue.h>
#include <linux/can.h>
#include <linux/can/skb.h>

@@ -85,6 +86,7 @@ struct slcan {
struct tty_struct *tty; /* ptr to TTY structure */
struct net_device *dev; /* easy for intr handling */
spinlock_t lock;
+ struct work_struct tx_work; /* Flushes transmit buffer */

/* These are pointers to the malloc()ed frame buffers. */
unsigned char rbuff[SLC_MTU]; /* receiver buffer */
@@ -309,36 +311,46 @@ static void slc_encaps(struct slcan *sl,
sl->dev->stats.tx_bytes += cf->can_dlc;
}

-/*
- * Called by the driver when there's room for more data. If we have
- * more packets to send, we send them here.
- */
-static void slcan_write_wakeup(struct tty_struct *tty)
+/* Write out any remaining transmit buffer. Scheduled when tty is writable */
+static void slcan_transmit(struct work_struct *work)
{
+ struct slcan *sl = container_of(work, struct slcan, tx_work);
int actual;
- struct slcan *sl = (struct slcan *) tty->disc_data;

+ spin_lock_bh(&sl->lock);
/* First make sure we're connected. */
- if (!sl || sl->magic != SLCAN_MAGIC || !netif_running(sl->dev))
+ if (!sl->tty || sl->magic != SLCAN_MAGIC || !netif_running(sl->dev)) {
+ spin_unlock_bh(&sl->lock);
return;
+ }

- spin_lock_bh(&sl->lock);
if (sl->xleft <= 0) {
/* Now serial buffer is almost free & we can start
* transmission of another packet */
sl->dev->stats.tx_packets++;
- clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+ clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
spin_unlock_bh(&sl->lock);
netif_wake_queue(sl->dev);
return;
}

- actual = tty->ops->write(tty, sl->xhead, sl->xleft);
+ actual = sl->tty->ops->write(sl->tty, sl->xhead, sl->xleft);
sl->xleft -= actual;
sl->xhead += actual;
spin_unlock_bh(&sl->lock);
}

+/*
+ * Called by the driver when there's room for more data.
+ * Schedule the transmit.
+ */
+static void slcan_write_wakeup(struct tty_struct *tty)
+{
+ struct slcan *sl = tty->disc_data;
+
+ schedule_work(&sl->tx_work);
+}
+
/* Send a can_frame to a TTY queue. */
static netdev_tx_t slc_xmit(struct sk_buff *skb, struct net_device *dev)
{
@@ -528,6 +540,7 @@ static struct slcan *slc_alloc(dev_t lin
sl->magic = SLCAN_MAGIC;
sl->dev = dev;
spin_lock_init(&sl->lock);
+ INIT_WORK(&sl->tx_work, slcan_transmit);
slcan_devs[i] = dev;

return sl;
@@ -626,8 +639,12 @@ static void slcan_close(struct tty_struc
if (!sl || sl->magic != SLCAN_MAGIC || sl->tty != tty)
return;

+ spin_lock_bh(&sl->lock);
tty->disc_data = NULL;
sl->tty = NULL;
+ spin_unlock_bh(&sl->lock);
+
+ flush_work(&sl->tx_work);

/* Flush network side */
unregister_netdev(sl->dev);