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Date:	Fri,  8 Aug 2014 12:25:52 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	Tyler Hall <tylerwhall@...il.com>
Cc:	Oliver Hartkopp <socketcan@...tkopp.net>,
	Andre Naujoks <nautsch2@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, Kamal Mostafa <kamal@...onical.com>,
	kernel-team@...ts.ubuntu.com
Subject: [3.13.y.z extended stable] Patch "slcan: Port write_wakeup deadlock fix from slip" has been added to staging queue

This is a note to let you know that I have just added a patch titled

    slcan: Port write_wakeup deadlock fix from slip

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.6.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 0ddb6fc2e77210638e924b57faabbe5f6a57a9c5 Mon Sep 17 00:00:00 2001
From: Tyler Hall <tylerwhall@...il.com>
Date: Sun, 15 Jun 2014 22:23:17 -0400
Subject: slcan: Port write_wakeup deadlock fix from slip

[ 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@...il.com>
Cc: Oliver Hartkopp <socketcan@...tkopp.net>
Cc: Andre Naujoks <nautsch2@...il.com>
Cc: David S. Miller <davem@...emloft.net>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/net/can/slcan.c | 41 +++++++++++++++++++++++++++++------------
 1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/drivers/net/can/slcan.c b/drivers/net/can/slcan.c
index 25377e5..3c28d1f 100644
--- a/drivers/net/can/slcan.c
+++ b/drivers/net/can/slcan.c
@@ -54,6 +54,7 @@
 #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>

@@ -87,6 +88,7 @@ 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	     */
@@ -311,34 +313,44 @@ 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(&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);
-		spin_unlock(&sl->lock);
+		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(&sl->lock);
+	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. */
@@ -524,6 +536,7 @@ 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;
@@ -622,8 +635,12 @@ 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);
--
1.9.1

--
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