[PATCH 1/2] slip: Fix deadlock in write_wakeup

[<c0410b7c>] (spin_bug+0x0/0x38) from [<c006109c>] (do_raw_spin_lock+0x60/0x1d0)
 r5:eab27000 r4:ec02754c
[<c006103c>] (do_raw_spin_lock+0x0/0x1d0) from [<c04185c0>] (_raw_spin_lock+0x28/0x2c)
 r10:0000001f r9:eabb814c r8:eabb8140 r7:40070193 r6:ec02754c r5:eab27000
 r4:ec02754c r3:00000000
[<c0418598>] (_raw_spin_lock+0x0/0x2c) from [<bf3a0220>] (slip_write_wakeup+0x50/0xe0 [slip])
 r4:ec027540 r3:00000003
[<bf3a01d0>] (slip_write_wakeup+0x0/0xe0 [slip]) from [<c026e420>] (tty_wakeup+0x48/0x68)
 r6:00000000 r5:ea80c480 r4:eab27000 r3:bf3a01d0
[<c026e3d8>] (tty_wakeup+0x0/0x68) from [<c028a8ec>] (uart_write_wakeup+0x2c/0x30)
 r5:ed68ea90 r4:c06790d8
[<c028a8c0>] (uart_write_wakeup+0x0/0x30) from [<c028dc44>] (serial8250_tx_chars+0x114/0x170)
[<c028db30>] (serial8250_tx_chars+0x0/0x170) from [<c028dffc>] (serial8250_handle_irq+0xa0/0xbc)
 r6:000000c2 r5:00000060 r4:c06790d8 r3:00000000
[<c028df5c>] (serial8250_handle_irq+0x0/0xbc) from [<c02933a4>] (dw8250_handle_irq+0x38/0x64)
 r7:00000000 r6:edd2f390 r5:000000c2 r4:c06790d8
[<c029336c>] (dw8250_handle_irq+0x0/0x64) from [<c028d2f4>] (serial8250_interrupt+0x44/0xc4)
 r6:00000000 r5:00000000 r4:c06791c4 r3:c029336c
[<c028d2b0>] (serial8250_interrupt+0x0/0xc4) from [<c0067fe4>] (handle_irq_event_percpu+0xb4/0x2b0)
 r10:c06790d8 r9:eab27000 r8:00000000 r7:00000000 r6:0000001f r5:edd52980
 r4:ec53b6c0 r3:c028d2b0
[<c0067f30>] (handle_irq_event_percpu+0x0/0x2b0) from [<c006822c>] (handle_irq_event+0x4c/0x6c)
 r10:c06790d8 r9:eab27000 r8:c0673ae0 r7:c05c2020 r6:ec53b6c0 r5:edd529d4
 r4:edd52980
[<c00681e0>] (handle_irq_event+0x0/0x6c) from [<c006b140>] (handle_level_irq+0xe8/0x100)
 r6:00000000 r5:edd529d4 r4:edd52980 r3:00022000
[<c006b058>] (handle_level_irq+0x0/0x100) from [<c00676f8>] (generic_handle_irq+0x30/0x40)
 r5:0000001f r4:0000001f
[<c00676c8>] (generic_handle_irq+0x0/0x40) from [<c000f57c>] (handle_IRQ+0xd0/0x13c)
 r4:ea997b18 r3:000000e0
[<c000f4ac>] (handle_IRQ+0x0/0x13c) from [<c00086c4>] (armada_370_xp_handle_irq+0x4c/0x118)
 r8:000003ff r7:ea997b18 r6:ffffffff r5:60070013 r4:c0674dc0
[<c0008678>] (armada_370_xp_handle_irq+0x0/0x118) from [<c0013840>] (__irq_svc+0x40/0x70)
Exception stack(0xea997b18 to 0xea997b60)
7b00:                                                       00000001 20070013
7b20: 00000000 0000000b 20070013 eab27000 20070013 00000000 ed10103e eab27000
7b40: c06790d8 ea997b74 ea997b60 ea997b60 c04186c0 c04186c8 60070013 ffffffff
 r9:eab27000 r8:ed10103e r7:ea997b4c r6:ffffffff r5:60070013 r4:c04186c8
[<c04186a4>] (_raw_spin_unlock_irqrestore+0x0/0x54) from [<c0288fc0>] (uart_start+0x40/0x44)
 r4:c06790d8 r3:c028ddd8
[<c0288f80>] (uart_start+0x0/0x44) from [<c028982c>] (uart_write+0xe4/0xf4)
 r6:0000003e r5:00000000 r4:ed68ea90 r3:0000003e
[<c0289748>] (uart_write+0x0/0xf4) from [<bf3a0d20>] (sl_xmit+0x1c4/0x228 [slip])
 r10:ed388e60 r9:0000003c r8:ffffffdd r7:0000003e r6:ec02754c r5:ea717eb8
 r4:ec027000
[<bf3a0b5c>] (sl_xmit+0x0/0x228 [slip]) from [<c0368d74>] (dev_hard_start_xmit+0x39c/0x6d0)
 r8:eaf163c0 r7:ec027000 r6:ea717eb8 r5:00000000 r4:00000000

Signed-off-by: Tyler Hall <redacted>
Cc: Oliver Hartkopp <socketcan@hartkopp.net>
Cc: Andre Naujoks <redacted>
Cc: David S. Miller <davem@davemloft.net>
Cc: linux-kernel@vger.kernel.org
---
 drivers/net/slip/slip.c | 36 ++++++++++++++++++++++++++----------
 drivers/net/slip/slip.h |  1 +
 2 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/drivers/net/slip/slip.c b/drivers/net/slip/slip.c
index ad4a94e..8752644 100644
--- a/drivers/net/slip/slip.c
+++ b/drivers/net/slip/slip.c

@@ -83,6 +83,7 @@
 #include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/slab.h>
+#include <linux/workqueue.h>
 #include "slip.h"
 #ifdef CONFIG_INET
 #include <linux/ip.h>

@@ -416,36 +417,46 @@ static void sl_encaps(struct slip *sl, unsigned char *icp, int len)
 #endif
 }
 
-/*
- * Called by the driver when there's room for more data.  If we have
- * more packets to send, we send them here.
- */
-static void slip_write_wakeup(struct tty_struct *tty)
+/* Write out any remaining transmit buffer. Scheduled when tty is writable */
+static void slip_transmit(struct work_struct *work)
 {
+	struct slip *sl = container_of(work, struct slip, tx_work);
 	int actual;
-	struct slip *sl = tty->disc_data;
 
+	spin_lock_bh(&sl->lock);
 	/* First make sure we're connected. */
-	if (!sl || sl->magic != SLIP_MAGIC || !netif_running(sl->dev))
+	if (!sl->tty || sl->magic != SLIP_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);
 		sl_unlock(sl);
 		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 slip_write_wakeup(struct tty_struct *tty)
+{
+	struct slip *sl = tty->disc_data;
+
+	schedule_work(&sl->tx_work);
+}
+
 static void sl_tx_timeout(struct net_device *dev)
 {
 	struct slip *sl = netdev_priv(dev);

@@ -749,6 +760,7 @@ static struct slip *sl_alloc(dev_t line)
 	sl->magic       = SLIP_MAGIC;
 	sl->dev	      	= dev;
 	spin_lock_init(&sl->lock);
+	INIT_WORK(&sl->tx_work, slip_transmit);
 	sl->mode        = SL_MODE_DEFAULT;
 #ifdef CONFIG_SLIP_SMART
 	/* initialize timer_list struct */

@@ -872,8 +884,12 @@ static void slip_close(struct tty_struct *tty)
 	if (!sl || sl->magic != SLIP_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);
 
 	/* VSV = very important to remove timers */
 #ifdef CONFIG_SLIP_SMART

diff --git a/drivers/net/slip/slip.h b/drivers/net/slip/slip.h
index 67673cf..cf32aad 100644
--- a/drivers/net/slip/slip.h
+++ b/drivers/net/slip/slip.h

@@ -53,6 +53,7 @@ struct slip {
   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	*/
 
 #ifdef SL_INCLUDE_CSLIP
   struct slcompress	*slcomp;	/* for header compression 	*/

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

diff --git a/drivers/net/can/slcan.c b/drivers/net/can/slcan.c
index dcf9196..ea4d4f1 100644
--- 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, struct can_frame *cf)
 	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 line)
 	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_struct *tty)
 	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);