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Remove private locks to avoid possible deadlock

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  Remove private locks to avoid possible deadlock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-07 21:10 +0100
    [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-07 21:10 +0100
      Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Francois Romieu <romieu@fr.zoreil.com> - 2016-12-08 00:20 +0100
        Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-08 21:40 +0100
          Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-08 23:00 +0100
            Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-08 23:20 +0100
              Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-08 23:20 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-08 23:50 +0100
          Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Francois Romieu <romieu@fr.zoreil.com> - 2016-12-09 00:30 +0100
            Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-09 12:30 +0100
              Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-10 03:30 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-11 21:20 +0100
                  Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-15 20:30 +0100
                    Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-15 22:20 +0100
                      Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-15 22:40 +0100
                        Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-15 23:40 +0100
                          Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-17 18:40 +0100
                            Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Francois Romieu <romieu@fr.zoreil.com> - 2016-12-18 01:20 +0100
                              Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-18 17:20 +0100
                                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-18 18:30 +0100
                                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-18 19:40 +0100
                                  Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-19 23:50 +0100
                                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-18 21:20 +0100
                              Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-19 11:10 +0100
                                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Francois Romieu <romieu@fr.zoreil.com> - 2016-12-20 01:10 +0100
    [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-07 21:10 +0100
      Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-07 22:00 +0100
      Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-07 22:00 +0100
      Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-07 22:40 +0100
        Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-07 22:50 +0100
          Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-07 23:40 +0100
            Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-08 00:30 +0100
        Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock David Miller <davem@davemloft.net> - 2016-12-08 00:50 +0100
          Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-08 15:20 +0100
            Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock David Miller <davem@davemloft.net> - 2016-12-08 16:30 +0100
              Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-08 17:00 +0100

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#1538046 — Remove private locks to avoid possible deadlock

Hi,

these patches fix possible deadlock situations in the sxgbe and stmmac
driver. Please note that the patches are only compile tested so it would
be great if someone could do tests with the concerning HW.

Regards,
Lino

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#1538048 — [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

The driver uses a private lock for synchronization between the xmit
function and the xmit completion handler, but since the NETIF_F_LLTX flag
is not set, the xmit function is also called with the xmit_lock held.

On the other hand the xmit completion handler first takes the private lock
and (in case that the tx queue has been stopped) the xmit_lock, leading
to a reverse locking order and the potential danger of a deadlock.

Fix this by removing the private lock completely and synchronizing the xmit
function and completion handler solely by means of the xmit_lock. By doing
this also remove the now unnecessary double check for a stopped tx queue.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
---
 drivers/net/ethernet/samsung/sxgbe/sxgbe_common.h |  1 -
 drivers/net/ethernet/samsung/sxgbe/sxgbe_main.c   | 27 +++++------------------
 2 files changed, 6 insertions(+), 22 deletions(-)

diff --git a/drivers/net/ethernet/samsung/sxgbe/sxgbe_common.h b/drivers/net/ethernet/samsung/sxgbe/sxgbe_common.h
index 5cb51b6..c61f260 100644
--- a/drivers/net/ethernet/samsung/sxgbe/sxgbe_common.h
+++ b/drivers/net/ethernet/samsung/sxgbe/sxgbe_common.h
@@ -384,7 +384,6 @@ struct sxgbe_tx_queue {
 	dma_addr_t *tx_skbuff_dma;
 	struct sk_buff **tx_skbuff;
 	struct timer_list txtimer;
-	spinlock_t tx_lock;	/* lock for tx queues */
 	unsigned int cur_tx;
 	unsigned int dirty_tx;
 	u32 tx_count_frames;
diff --git a/drivers/net/ethernet/samsung/sxgbe/sxgbe_main.c b/drivers/net/ethernet/samsung/sxgbe/sxgbe_main.c
index ea44a24..22d3b0b 100644
--- a/drivers/net/ethernet/samsung/sxgbe/sxgbe_main.c
+++ b/drivers/net/ethernet/samsung/sxgbe/sxgbe_main.c
@@ -426,9 +426,6 @@ static int init_tx_ring(struct device *dev, u8 queue_no,
 	tx_ring->dirty_tx = 0;
 	tx_ring->cur_tx = 0;
 
-	/* initialise TX queue lock */
-	spin_lock_init(&tx_ring->tx_lock);
-
 	return 0;
 
 dmamem_err:
@@ -743,7 +740,7 @@ static void sxgbe_tx_queue_clean(struct sxgbe_tx_queue *tqueue)
 
 	dev_txq = netdev_get_tx_queue(priv->dev, queue_no);
 
-	spin_lock(&tqueue->tx_lock);
+	__netif_tx_lock(dev_txq, smp_processor_id());
 
 	priv->xstats.tx_clean++;
 	while (tqueue->dirty_tx != tqueue->cur_tx) {
@@ -781,18 +778,13 @@ static void sxgbe_tx_queue_clean(struct sxgbe_tx_queue *tqueue)
 
 	/* wake up queue */
 	if (unlikely(netif_tx_queue_stopped(dev_txq) &&
-		     sxgbe_tx_avail(tqueue, tx_rsize) > SXGBE_TX_THRESH(priv))) {
-		netif_tx_lock(priv->dev);
-		if (netif_tx_queue_stopped(dev_txq) &&
-		    sxgbe_tx_avail(tqueue, tx_rsize) > SXGBE_TX_THRESH(priv)) {
-			if (netif_msg_tx_done(priv))
-				pr_debug("%s: restart transmit\n", __func__);
-			netif_tx_wake_queue(dev_txq);
-		}
-		netif_tx_unlock(priv->dev);
+	    sxgbe_tx_avail(tqueue, tx_rsize) > SXGBE_TX_THRESH(priv))) {
+		if (netif_msg_tx_done(priv))
+			pr_debug("%s: restart transmit\n", __func__);
+		netif_tx_wake_queue(dev_txq);
 	}
 
-	spin_unlock(&tqueue->tx_lock);
+	__netif_tx_unlock(dev_txq);
 }
 
 /**
@@ -1304,9 +1296,6 @@ static netdev_tx_t sxgbe_xmit(struct sk_buff *skb, struct net_device *dev)
 		      tqueue->hwts_tx_en)))
 		ctxt_desc_req = 1;
 
-	/* get the spinlock */
-	spin_lock(&tqueue->tx_lock);
-
 	if (priv->tx_path_in_lpi_mode)
 		sxgbe_disable_eee_mode(priv);
 
@@ -1316,8 +1305,6 @@ static netdev_tx_t sxgbe_xmit(struct sk_buff *skb, struct net_device *dev)
 			netdev_err(dev, "%s: Tx Ring is full when %d queue is awake\n",
 				   __func__, txq_index);
 		}
-		/* release the spin lock in case of BUSY */
-		spin_unlock(&tqueue->tx_lock);
 		return NETDEV_TX_BUSY;
 	}
 
@@ -1436,8 +1423,6 @@ static netdev_tx_t sxgbe_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	priv->hw->dma->enable_dma_transmission(priv->ioaddr, txq_index);
 
-	spin_unlock(&tqueue->tx_lock);
-
 	return NETDEV_TX_OK;
 }
 
-- 
1.9.1

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#1538165 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

Lino Sanfilippo <LinoSanfilippo@gmx.de> :
> The driver uses a private lock for synchronization between the xmit
> function and the xmit completion handler, but since the NETIF_F_LLTX flag
> is not set, the xmit function is also called with the xmit_lock held.
> 
> On the other hand the xmit completion handler first takes the private lock
> and (in case that the tx queue has been stopped) the xmit_lock, leading
> to a reverse locking order and the potential danger of a deadlock.

netif_tx_stop_queue is used by:
1. xmit function before releasing lock and returning.
2. sxgbe_restart_tx_queue()
   <- sxgbe_tx_interrupt
   <- sxgbe_reset_all_tx_queues()
      <- sxgbe_tx_timeout()

Given xmit won't be called again until tx queue is enabled, it's not clear
how a deadlock could happen due to #1.

Regardless of deadlocks anywhere else, #2 has some serious problem due to
the lack of exclusion between the tx queue restart handler and the xmit
handler.

-- 
Ueimor

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#1538864 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

Hi,

On 08.12.2016 00:15, Francois Romieu wrote:
> Lino Sanfilippo <LinoSanfilippo@gmx.de> :
>> The driver uses a private lock for synchronization between the xmit
>> function and the xmit completion handler, but since the NETIF_F_LLTX flag
>> is not set, the xmit function is also called with the xmit_lock held.
>> 
>> On the other hand the xmit completion handler first takes the private lock
>> and (in case that the tx queue has been stopped) the xmit_lock, leading
>> to a reverse locking order and the potential danger of a deadlock.
> 
> netif_tx_stop_queue is used by:
> 1. xmit function before releasing lock and returning.
> 2. sxgbe_restart_tx_queue()
>    <- sxgbe_tx_interrupt
>    <- sxgbe_reset_all_tx_queues()
>       <- sxgbe_tx_timeout()
> 
> Given xmit won't be called again until tx queue is enabled, it's not clear
> how a deadlock could happen due to #1.
> 


After spending more thoughts on this I tend to agree with you. Yes, we have the
different locking order for the xmit_lock and the private lock in two concurrent
threads. And one of the first things one learns about locking is that this is a
good way to create a deadlock sooner or later. But in our case the deadlock 
can only occur if the xmit function and the tx completion handler perceive different
 states for the tx queue, or to be more specific: 
the completion handler sees the tx queue in state "stopped" while the xmit handler 
sees it in state "running" at the same time. Only then both functions would try to
take both locks, which could lead to a deadlock.

OTOH Pavel said that he actually could produce a deadlock. Now I wonder if this is caused
by that locking scheme (in a way I have not figured out yet) or if it is a different issue.

Regards,
Lino

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#1538907 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

[Multipart message — attachments visible in raw view] — view raw

On Thu 2016-12-08 21:32:12, Lino Sanfilippo wrote:
> Hi,
> 
> On 08.12.2016 00:15, Francois Romieu wrote:
> > Lino Sanfilippo <LinoSanfilippo@gmx.de> :
> >> The driver uses a private lock for synchronization between the xmit
> >> function and the xmit completion handler, but since the NETIF_F_LLTX flag
> >> is not set, the xmit function is also called with the xmit_lock held.
> >> 
> >> On the other hand the xmit completion handler first takes the private lock
> >> and (in case that the tx queue has been stopped) the xmit_lock, leading
> >> to a reverse locking order and the potential danger of a deadlock.
> > 
> > netif_tx_stop_queue is used by:
> > 1. xmit function before releasing lock and returning.
> > 2. sxgbe_restart_tx_queue()
> >    <- sxgbe_tx_interrupt
> >    <- sxgbe_reset_all_tx_queues()
> >       <- sxgbe_tx_timeout()
> > 
> > Given xmit won't be called again until tx queue is enabled, it's not clear
> > how a deadlock could happen due to #1.
> > 
> 
> 
> After spending more thoughts on this I tend to agree with you. Yes, we have the
> different locking order for the xmit_lock and the private lock in two concurrent
> threads. And one of the first things one learns about locking is that this is a
> good way to create a deadlock sooner or later. But in our case the deadlock 
> can only occur if the xmit function and the tx completion handler perceive different
>  states for the tx queue, or to be more specific: 
> the completion handler sees the tx queue in state "stopped" while the xmit handler 
> sees it in state "running" at the same time. Only then both functions would try to
> take both locks, which could lead to a deadlock.
> 
> OTOH Pavel said that he actually could produce a deadlock. Now I wonder if this is caused
> by that locking scheme (in a way I have not figured out yet) or if it is a different issue.

Pavel has some problems, but that's on different hardware.. and it is
possible that it is deadlock (or something else) somewhere else.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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#1538920 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

Hi,

On 08.12.2016 22:54, Pavel Machek wrote:
> On Thu 2016-12-08 21:32:12, Lino Sanfilippo wrote:
>> Hi,
>> 
>> On 08.12.2016 00:15, Francois Romieu wrote:
>> > Lino Sanfilippo <LinoSanfilippo@gmx.de> :
>> >> The driver uses a private lock for synchronization between the xmit
>> >> function and the xmit completion handler, but since the NETIF_F_LLTX flag
>> >> is not set, the xmit function is also called with the xmit_lock held.
>> >> 
>> >> On the other hand the xmit completion handler first takes the private lock
>> >> and (in case that the tx queue has been stopped) the xmit_lock, leading
>> >> to a reverse locking order and the potential danger of a deadlock.
>> > 
>> > netif_tx_stop_queue is used by:
>> > 1. xmit function before releasing lock and returning.
>> > 2. sxgbe_restart_tx_queue()
>> >    <- sxgbe_tx_interrupt
>> >    <- sxgbe_reset_all_tx_queues()
>> >       <- sxgbe_tx_timeout()
>> > 
>> > Given xmit won't be called again until tx queue is enabled, it's not clear
>> > how a deadlock could happen due to #1.
>> > 
>> 
>> 
>> After spending more thoughts on this I tend to agree with you. Yes, we have the
>> different locking order for the xmit_lock and the private lock in two concurrent
>> threads. And one of the first things one learns about locking is that this is a
>> good way to create a deadlock sooner or later. But in our case the deadlock 
>> can only occur if the xmit function and the tx completion handler perceive different
>>  states for the tx queue, or to be more specific: 
>> the completion handler sees the tx queue in state "stopped" while the xmit handler 
>> sees it in state "running" at the same time. Only then both functions would try to
>> take both locks, which could lead to a deadlock.
>> 
>> OTOH Pavel said that he actually could produce a deadlock. Now I wonder if this is caused
>> by that locking scheme (in a way I have not figured out yet) or if it is a different issue.
> 
> Pavel has some problems, but that's on different hardware.. and it is
> possible that it is deadlock (or something else) somewhere else.
> 

Right, it is different hardware. But the locking situation in xmit function and tx completion handler
is very similar in both drivers. So if a deadlock is not possible in sxgbe it should 
also not be possible in stmmac (at least not due to the different locking order). 
So maybe there is no real issue that we could fix with removing the private lock and we should
keep it as it is.

Regards,
Lino

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#1538921 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

[Multipart message — attachments visible in raw view] — view raw

On Thu 2016-12-08 23:12:10, Lino Sanfilippo wrote:
> Hi,
> 
> On 08.12.2016 22:54, Pavel Machek wrote:
> > On Thu 2016-12-08 21:32:12, Lino Sanfilippo wrote:
> >> Hi,
> >> 
> >> On 08.12.2016 00:15, Francois Romieu wrote:
> >> > Lino Sanfilippo <LinoSanfilippo@gmx.de> :
> >> >> The driver uses a private lock for synchronization between the xmit
> >> >> function and the xmit completion handler, but since the NETIF_F_LLTX flag
> >> >> is not set, the xmit function is also called with the xmit_lock held.
> >> >> 
> >> >> On the other hand the xmit completion handler first takes the private lock
> >> >> and (in case that the tx queue has been stopped) the xmit_lock, leading
> >> >> to a reverse locking order and the potential danger of a deadlock.
> >> > 
> >> > netif_tx_stop_queue is used by:
> >> > 1. xmit function before releasing lock and returning.
> >> > 2. sxgbe_restart_tx_queue()
> >> >    <- sxgbe_tx_interrupt
> >> >    <- sxgbe_reset_all_tx_queues()
> >> >       <- sxgbe_tx_timeout()
> >> > 
> >> > Given xmit won't be called again until tx queue is enabled, it's not clear
> >> > how a deadlock could happen due to #1.
> >> > 
> >> 
> >> 
> >> After spending more thoughts on this I tend to agree with you. Yes, we have the
> >> different locking order for the xmit_lock and the private lock in two concurrent
> >> threads. And one of the first things one learns about locking is that this is a
> >> good way to create a deadlock sooner or later. But in our case the deadlock 
> >> can only occur if the xmit function and the tx completion handler perceive different
> >>  states for the tx queue, or to be more specific: 
> >> the completion handler sees the tx queue in state "stopped" while the xmit handler 
> >> sees it in state "running" at the same time. Only then both functions would try to
> >> take both locks, which could lead to a deadlock.
> >> 
> >> OTOH Pavel said that he actually could produce a deadlock. Now I wonder if this is caused
> >> by that locking scheme (in a way I have not figured out yet) or if it is a different issue.
> > 
> > Pavel has some problems, but that's on different hardware.. and it is
> > possible that it is deadlock (or something else) somewhere else.
> > 
> 
> Right, it is different hardware. But the locking situation in xmit function and tx completion handler
> is very similar in both drivers. So if a deadlock is not possible in sxgbe it should 
> also not be possible in stmmac (at least not due to the different locking order). 
> So maybe there is no real issue that we could fix with removing the private lock and we should
> keep it as it is.

Well.. the locking is pretty confused there. Having private lock that
mirrors lock from network layer is confusing and ugly... that should
be reason to fix it.
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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#1538936 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

On 08.12.2016 23:18, Pavel Machek wrote:
> On Thu 2016-12-08 23:12:10, Lino Sanfilippo wrote:
>> Hi,
>> 
>> On 08.12.2016 22:54, Pavel Machek wrote:
>> > On Thu 2016-12-08 21:32:12, Lino Sanfilippo wrote:
>> >> Hi,
>> >> 
>> >> On 08.12.2016 00:15, Francois Romieu wrote:
>> >> > Lino Sanfilippo <LinoSanfilippo@gmx.de> :
>> >> >> The driver uses a private lock for synchronization between the xmit
>> >> >> function and the xmit completion handler, but since the NETIF_F_LLTX flag
>> >> >> is not set, the xmit function is also called with the xmit_lock held.
>> >> >> 
>> >> >> On the other hand the xmit completion handler first takes the private lock
>> >> >> and (in case that the tx queue has been stopped) the xmit_lock, leading
>> >> >> to a reverse locking order and the potential danger of a deadlock.
>> >> > 
>> >> > netif_tx_stop_queue is used by:
>> >> > 1. xmit function before releasing lock and returning.
>> >> > 2. sxgbe_restart_tx_queue()
>> >> >    <- sxgbe_tx_interrupt
>> >> >    <- sxgbe_reset_all_tx_queues()
>> >> >       <- sxgbe_tx_timeout()
>> >> > 
>> >> > Given xmit won't be called again until tx queue is enabled, it's not clear
>> >> > how a deadlock could happen due to #1.
>> >> > 
>> >> 
>> >> 
>> >> After spending more thoughts on this I tend to agree with you. Yes, we have the
>> >> different locking order for the xmit_lock and the private lock in two concurrent
>> >> threads. And one of the first things one learns about locking is that this is a
>> >> good way to create a deadlock sooner or later. But in our case the deadlock 
>> >> can only occur if the xmit function and the tx completion handler perceive different
>> >>  states for the tx queue, or to be more specific: 
>> >> the completion handler sees the tx queue in state "stopped" while the xmit handler 
>> >> sees it in state "running" at the same time. Only then both functions would try to
>> >> take both locks, which could lead to a deadlock.
>> >> 
>> >> OTOH Pavel said that he actually could produce a deadlock. Now I wonder if this is caused
>> >> by that locking scheme (in a way I have not figured out yet) or if it is a different issue.
>> > 
>> > Pavel has some problems, but that's on different hardware.. and it is
>> > possible that it is deadlock (or something else) somewhere else.
>> > 
>> 
>> Right, it is different hardware. But the locking situation in xmit function and tx completion handler
>> is very similar in both drivers. So if a deadlock is not possible in sxgbe it should 
>> also not be possible in stmmac (at least not due to the different locking order). 
>> So maybe there is no real issue that we could fix with removing the private lock and we should
>> keep it as it is.
> 
> Well.. the locking is pretty confused there. Having private lock that
> mirrors lock from network layer is confusing and ugly... that should
> be reason to fix it.
> 									Pavel
> 

Ok. Then I will resend the patches for both drivers with a different (less dramatic) commit message
in which the change is not longer described as a fix for deadlock but rather as a code 
cleanup/improvement, ok?

Regards,
Lino

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#1538954 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

Lino Sanfilippo <LinoSanfilippo@gmx.de> :
[...]
> OTOH Pavel said that he actually could produce a deadlock. Now I wonder if
> this is caused by that locking scheme (in a way I have not figured out yet)
> or if it is a different issue.

stmmac_tx_err races with stmmac_xmit.

-- 
Ueimor

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#1539291 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

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On Fri 2016-12-09 00:19:43, Francois Romieu wrote:
> Lino Sanfilippo <LinoSanfilippo@gmx.de> :
> [...]
> > OTOH Pavel said that he actually could produce a deadlock. Now I wonder if
> > this is caused by that locking scheme (in a way I have not figured out yet)
> > or if it is a different issue.
> 
> stmmac_tx_err races with stmmac_xmit.

Umm, yes, that looks real.

And that means that removing tx_lock will not be completely trivial
:-(. Lino, any ideas there?

netif_tx_lock_irqsave() would help, but afaict that one does not
exist.

Plus, does someone know how to trigger the status == tx_hard_error? I
tried powering down the switch, but that did not do it.

Thanks,								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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#1539759 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

Hi,

On 09.12.2016 12:21, Pavel Machek wrote:
> On Fri 2016-12-09 00:19:43, Francois Romieu wrote:
>> Lino Sanfilippo <LinoSanfilippo@gmx.de> :
>> [...]
>> > OTOH Pavel said that he actually could produce a deadlock. Now I wonder if
>> > this is caused by that locking scheme (in a way I have not figured out yet)
>> > or if it is a different issue.
>> 
>> stmmac_tx_err races with stmmac_xmit.
> 
> Umm, yes, that looks real.
> 
> And that means that removing tx_lock will not be completely trivial
> :-(. Lino, any ideas there?
> 

Ok, the race is there but it looks like a problem that is not related to 
the use or removal of the private lock.
By a glimpse into other drivers (e.g sky2 or e1000), a possible way to handle a 
tx error is to start a separate task and restart the tx path in that task instead
the irq handler (or timer in case of the watchdog).

In that task we could do:
1. deactivate napi
2. deactivate irqs
3. wait for running napi/irqs do complete (_sync)
4. call stmmac_tx_err()
5. reenable napi
6. reenable irqs

We have to ensure that no xmit() is executing while stmmac_tx_err() does the cleanup,
so stmmac_tx_err() should IMO rather call netif_tx_disable() instead of netif_stop_queue()
(the former grabs the xmit lock before it sets __QUEUE_STATE_DRV_XOFF to disable
the queue).

Regards,
Lino

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#1540059 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

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Hi!

> On 09.12.2016 12:21, Pavel Machek wrote:
> > On Fri 2016-12-09 00:19:43, Francois Romieu wrote:
> >> Lino Sanfilippo <LinoSanfilippo@gmx.de> :
> >> [...]
> >> > OTOH Pavel said that he actually could produce a deadlock. Now I wonder if
> >> > this is caused by that locking scheme (in a way I have not figured out yet)
> >> > or if it is a different issue.
> >> 
> >> stmmac_tx_err races with stmmac_xmit.
> > 
> > Umm, yes, that looks real.
> > 
> > And that means that removing tx_lock will not be completely trivial
> > :-(. Lino, any ideas there?
> > 
> 
> Ok, the race is there but it looks like a problem that is not related to 
> the use or removal of the private lock.

Well, removal of the private lock will make it trickier to fix :-(.

> By a glimpse into other drivers (e.g sky2 or e1000), a possible way to handle a 
> tx error is to start a separate task and restart the tx path in that task instead
> the irq handler (or timer in case of the watchdog).
> 
> In that task we could do:
> 1. deactivate napi
> 2. deactivate irqs
> 3. wait for running napi/irqs do complete (_sync)
> 4. call stmmac_tx_err()
> 5. reenable napi
> 6. reenable irqs
> 
> We have to ensure that no xmit() is executing while stmmac_tx_err() does the cleanup,
> so stmmac_tx_err() should IMO rather call netif_tx_disable() instead of netif_stop_queue()
> (the former grabs the xmit lock before it sets __QUEUE_STATE_DRV_XOFF to disable
> the queue).

Do you understand what stmmac_tx_err(priv); is supposed to do? In
particular, if it is called while the driver is working ok -- should
the driver survive that?

Because it does not currently, and I don't know how to test that
code. Unplugging the cable does not provoke that.

I tried

        } else if (unlikely(status == tx_hard_error))
                stmmac_tx_err(priv);
+
+       {
+               static int i;
+               i++;
+               if (i==1000) {
+                       i = 0;
+                       printk("Simulated error\n");
+                       stmmac_tx_err(priv);
+               }
+       }
 }

but the driver does not survive that :-(.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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#1542993 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

Hi Pavel,

sorry for the late reply.

On 11.12.2016 21:11, Pavel Machek wrote:
> 
> Do you understand what stmmac_tx_err(priv); is supposed to do? In
> particular, if it is called while the driver is working ok -- should
> the driver survive that?

As far as I understood it is supposed to fixup an errorneous tx path, e.g. a
missing tx completion for transmitted frames.

Some drivers do this by restarting only the HW parts responsible for tx, some
others by restarting the complete hardware. 
But IMO it should also be ok to be called if the HW is still working fine.

> Because it does not currently, and I don't know how to test that
> code. Unplugging the cable does not provoke that.
> 
> I tried
> 
>         } else if (unlikely(status == tx_hard_error))
>                 stmmac_tx_err(priv);
> +
> +       {
> +               static int i;
> +               i++;
> +               if (i==1000) {
> +                       i = 0;
> +                       printk("Simulated error\n");
> +                       stmmac_tx_err(priv);
> +               }
> +       }
>  }
> 

Ok, there is this race that Francois mentioned so it is not surprising that
the driver does not survive the call of stmmac_tx_err() as it is called now.
Thats why I suggested to do a proper shutdown and restart of the tx path to
avoid the race.

Regards,
Lino

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#1543074 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

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Hi!

> sorry for the late reply.

No problem. Thanks for the help.

> On 11.12.2016 21:11, Pavel Machek wrote:
> > 
> > Do you understand what stmmac_tx_err(priv); is supposed to do? In
> > particular, if it is called while the driver is working ok -- should
> > the driver survive that?
> 
> As far as I understood it is supposed to fixup an errorneous tx path, e.g. a
> missing tx completion for transmitted frames.
> 
> Some drivers do this by restarting only the HW parts responsible for tx, some
> others by restarting the complete hardware. 
> But IMO it should also be ok to be called if the HW is still working fine.
> 
> > Because it does not currently, and I don't know how to test that
> > code. Unplugging the cable does not provoke that.
> > 
> > I tried
> > 
> >         } else if (unlikely(status == tx_hard_error))
> >                 stmmac_tx_err(priv);
> > +
> > +       {
> > +               static int i;
> > +               i++;
> > +               if (i==1000) {
> > +                       i = 0;
> > +                       printk("Simulated error\n");
> > +                       stmmac_tx_err(priv);
> > +               }
> > +       }
> >  }
> > 
> 
> Ok, there is this race that Francois mentioned so it is not surprising that
> the driver does not survive the call of stmmac_tx_err() as it is called now.
> Thats why I suggested to do a proper shutdown and restart of the tx path to
> avoid the race.

I actually did experiment with adding locking there, too, and no, no
luck. It seems stmmac_tx_err() is more broken than just locking.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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#1543078 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

On 15.12.2016 22:03, Pavel Machek wrote:

> 
> I actually did experiment with adding locking there, too, and no, no
> luck. It seems stmmac_tx_err() is more broken than just locking.
> 

Ah ok. Then maybe priv->hw->dma->stop_tx() does not do the job correctly (stop the
tx path properly) and the HW is still active on the tx path while the tx buffers are
freed. OTOH stmmac_release() also stops the phy before the tx (and rx) paths are stopped.
Did you try to stop the phy fist in stmmac_tx_err_work(), too?

Regards,
Lino

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#1543102 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

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On 15.12.2016 22:32, Lino Sanfilippo wrote:

> Ah ok. Then maybe priv->hw->dma->stop_tx() does not do the job correctly (stop the
> tx path properly) and the HW is still active on the tx path while the tx buffers are
> freed. OTOH stmmac_release() also stops the phy before the tx (and rx) paths are stopped.
> Did you try to stop the phy fist in stmmac_tx_err_work(), too?
> 
> Regards,
> Lino
> 

And this is the "sledgehammer" approach: Do a complete shutdown and restart
of the hardware in case of tx error (against net-next and only compile tested).

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#1544020 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

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On Thu 2016-12-15 23:33:22, Lino Sanfilippo wrote:
> On 15.12.2016 22:32, Lino Sanfilippo wrote:
> 
> > Ah ok. Then maybe priv->hw->dma->stop_tx() does not do the job correctly (stop the
> > tx path properly) and the HW is still active on the tx path while the tx buffers are
> > freed. OTOH stmmac_release() also stops the phy before the tx (and rx) paths are stopped.
> > Did you try to stop the phy fist in stmmac_tx_err_work(), too?
> > 
> > Regards,
> > Lino
> > 
> 
> And this is the "sledgehammer" approach: Do a complete shutdown and restart
> of the hardware in case of tx error (against net-next and only
>compile tested).

Wow, thanks a lot. I'll try to get the driver back to the non-working
state, and try it.

I believe I have some idea what is wrong there. (Missing memory barriers).

> +static void stmmac_tx_err_work(struct work_struct *work)
> +{
> +	struct stmmac_priv *priv = container_of(work, struct stmmac_priv,
> +						tx_err_work);
> +	/* restart netdev */
> +	rtnl_lock();
> +	stmmac_release(priv->dev);
> +	stmmac_open(priv->dev);
> +	rtnl_unlock();
> +}

Won't this up/down the interface, in a way userspace can observe?

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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#1544056 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

Pavel Machek <pavel@ucw.cz> :
[...]
> Won't this up/down the interface, in a way userspace can observe?

It won't up/down the interface as it doesn't exactly mimic what the
network code does (there's more than rtnl_lock).

For the same reason it's broken if it races with the transmit path: it
can release driver resources while the transmit path uses these.

Btw the points below may not matter/hurt much for a proof a concept
but they would need to be addressed as well:
1) unchecked (and avoidable) extra error paths due to stmmac_release()
2) racy cancel_work_sync. Low probability as it is, an irq + error could
   take place right after cancel_work_sync

Lino, have you considered via-rhine.c since its "move work from irq to
workqueue context" changes that started in
7ab87ff4c770eed71e3777936299292739fcd0fe [*] ?

It's a shameless plug - originated in r8169.c - but it should be rather
close to what the sxgbe and friends require. Thought / opinion ?

[*] Including fixes/changes in:
- 3a5a883a8a663b930908cae4abe5ec913b9b2fd2
- e1efa87241272104d6a12c8b9fcdc4f62634d447
- 810f19bcb862f8889b27e0c9d9eceac9593925dd
- e45af497950a89459a0c4b13ffd91e1729fffef4
- a926592f5e4e900f3fa903298c4619a131e60963
- 559bcac35facfed49ab4f408e162971612dcfdf3

-- 
Ueimor

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#1544162 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

Hi,

On 18.12.2016 01:15, Francois Romieu wrote:
> Pavel Machek <pavel@ucw.cz> :
> [...]
>> Won't this up/down the interface, in a way userspace can observe?
> 
> It won't up/down the interface as it doesn't exactly mimic what the
> network code does (there's more than rtnl_lock).
> 

Right. Userspace wont see link down/up, but it will see carrier off/on.
But this is AFAIK acceptable for a rare situation like a tx error.

> For the same reason it's broken if it races with the transmit path: it
> can release driver resources while the transmit path uses these.
> 
> Btw the points below may not matter/hurt much for a proof a concept
> but they would need to be addressed as well:
> 1) unchecked (and avoidable) extra error paths due to stmmac_release()
> 2) racy cancel_work_sync. Low probability as it is, an irq + error could
>    take place right after cancel_work_sync

It was indeed only meant as a proof of concept. Nevertheless the race is not 
good, since one can run into it when faking the tx error for testings purposes.
So below is a slightly improved version of the restart handling.
Its not meant as a final version either. But maybe we can use it as a starting
point.

> Lino, have you considered via-rhine.c since its "move work from irq to
> workqueue context" changes that started in
> 7ab87ff4c770eed71e3777936299292739fcd0fe [*] ?
> It's a shameless plug - originated in r8169.c - but it should be rather
> close to what the sxgbe and friends require. Thought / opinion ?
> 

Not really. There are a few drivers that I use to look into if I want to know
how certain things are done correctly (e.g the sky2 or the intel drivers) because
I think they are well implemented.
But you seem to have put some thoughts into various race condition problems
in the via-rhine driver and I can image that sxgbe and stmmac still have some
of these issues, too.

> [*] Including fixes/changes in:
> - 3a5a883a8a663b930908cae4abe5ec913b9b2fd2

Ok, the issues you fixed here are concerning the tx_curr and tx_dirty
pointers. For now this is not needed in stmmac and sxgbe since the
tx completion handlers in both drivers are not lock-free like in 
the via-rhine.c but are synchronized with xmit by means of the xmit_lock.

> - e1efa87241272104d6a12c8b9fcdc4f62634d447

Yep, a sync of the dma descriptors before the hardware gets ownership of the tx tail
idx is missing in the stmmac, too. 

> - 810f19bcb862f8889b27e0c9d9eceac9593925dd
> - e45af497950a89459a0c4b13ffd91e1729fffef4
> - a926592f5e4e900f3fa903298c4619a131e60963

I think we should use netif_tx_disable() instead of netif_stop_queue(), too, in 
case of restart to avoid a possible schedule of the xmit function while we restart. 
So this is also part of the new patch.

Again the patch is only compile tested.

Regards,
Lino

---
 drivers/net/ethernet/stmicro/stmmac/stmmac.h      |  1 +
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 95 +++++++++++++++--------
 2 files changed, 63 insertions(+), 33 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
index eab04ae..9c240d7 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
@@ -131,6 +131,7 @@ struct stmmac_priv {
 	u32 rx_tail_addr;
 	u32 tx_tail_addr;
 	u32 mss;
+	struct work_struct tx_err_work;
 
 #ifdef CONFIG_DEBUG_FS
 	struct dentry *dbgfs_dir;
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 3e40578..5762750 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -1403,37 +1403,6 @@ static inline void stmmac_disable_dma_irq(struct stmmac_priv *priv)
 }
 
 /**
- * stmmac_tx_err - to manage the tx error
- * @priv: driver private structure
- * Description: it cleans the descriptors and restarts the transmission
- * in case of transmission errors.
- */
-static void stmmac_tx_err(struct stmmac_priv *priv)
-{
-	int i;
-	netif_stop_queue(priv->dev);
-
-	priv->hw->dma->stop_tx(priv->ioaddr);
-	dma_free_tx_skbufs(priv);
-	for (i = 0; i < DMA_TX_SIZE; i++)
-		if (priv->extend_desc)
-			priv->hw->desc->init_tx_desc(&priv->dma_etx[i].basic,
-						     priv->mode,
-						     (i == DMA_TX_SIZE - 1));
-		else
-			priv->hw->desc->init_tx_desc(&priv->dma_tx[i],
-						     priv->mode,
-						     (i == DMA_TX_SIZE - 1));
-	priv->dirty_tx = 0;
-	priv->cur_tx = 0;
-	netdev_reset_queue(priv->dev);
-	priv->hw->dma->start_tx(priv->ioaddr);
-
-	priv->dev->stats.tx_errors++;
-	netif_wake_queue(priv->dev);
-}
-
-/**
  * stmmac_dma_interrupt - DMA ISR
  * @priv: driver private structure
  * Description: this is the DMA ISR. It is called by the main ISR.
@@ -1466,7 +1435,7 @@ static void stmmac_dma_interrupt(struct stmmac_priv *priv)
 			priv->xstats.threshold = tc;
 		}
 	} else if (unlikely(status == tx_hard_error))
-		stmmac_tx_err(priv);
+		schedule_work(&priv->tx_err_work);
 }
 
 /**
@@ -1902,6 +1871,7 @@ static int stmmac_release(struct net_device *dev)
 	if (priv->lpi_irq > 0)
 		free_irq(priv->lpi_irq, dev);
 
+	cancel_work_sync(&priv->tx_err_work);
 	/* Stop TX/RX DMA and clear the descriptors */
 	priv->hw->dma->stop_tx(priv->ioaddr);
 	priv->hw->dma->stop_rx(priv->ioaddr);
@@ -1920,9 +1890,67 @@ static int stmmac_release(struct net_device *dev)
 
 	stmmac_release_ptp(priv);
 
+
 	return 0;
 }
 
+static void stmmac_shutdown(struct net_device *dev)
+{
+	struct stmmac_priv *priv = netdev_priv(dev);
+
+	/* make sure xmit is not scheduled any more */
+	netif_tx_disable(dev);
+
+	if (priv->eee_enabled)
+		del_timer_sync(&priv->eee_ctrl_timer);
+
+	/* Stop and disconnect the PHY */
+	if (dev->phydev) {
+		phy_stop(dev->phydev);
+		phy_disconnect(dev->phydev);
+	}
+
+	napi_disable(&priv->napi);
+
+	del_timer_sync(&priv->txtimer);
+
+	/* Free the IRQ lines */
+	free_irq(dev->irq, dev);
+	if (priv->wol_irq != dev->irq)
+		free_irq(priv->wol_irq, dev);
+	if (priv->lpi_irq > 0)
+		free_irq(priv->lpi_irq, dev);
+
+	/* Stop TX/RX DMA and clear the descriptors */
+	priv->hw->dma->stop_tx(priv->ioaddr);
+	priv->hw->dma->stop_rx(priv->ioaddr);
+
+	/* Release and free the Rx/Tx resources */
+	free_dma_desc_resources(priv);
+
+	/* Disable the MAC Rx/Tx */
+	stmmac_set_mac(priv->ioaddr, false);
+
+	netif_carrier_off(dev);
+
+#ifdef CONFIG_DEBUG_FS
+	stmmac_exit_fs(dev);
+#endif
+
+	stmmac_release_ptp(priv);
+}
+
+static void stmmac_tx_err_work(struct work_struct *work)
+{
+	struct stmmac_priv *priv = container_of(work, struct stmmac_priv,
+						tx_err_work);
+	/* restart netdev */
+	rtnl_lock();
+	stmmac_shutdown(priv->dev);
+	stmmac_open(priv->dev);
+	rtnl_unlock();
+}
+
 /**
  *  stmmac_tso_allocator - close entry point of the driver
  *  @priv: driver private structure
@@ -2688,7 +2716,7 @@ static void stmmac_tx_timeout(struct net_device *dev)
 	struct stmmac_priv *priv = netdev_priv(dev);
 
 	/* Clear Tx resources and restart transmitting again */
-	stmmac_tx_err(priv);
+	schedule_work(&priv->tx_err_work);
 }
 
 /**
@@ -3338,6 +3366,7 @@ int stmmac_dvr_probe(struct device *device,
 	netif_napi_add(ndev, &priv->napi, stmmac_poll, 64);
 
 	spin_lock_init(&priv->lock);
+	INIT_WORK(&priv->tx_err_work, stmmac_tx_err_work);
 
 	ret = register_netdev(ndev);
 	if (ret) {
-- 
1.9.1

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#1544178 — Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

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Hi!

> > - e1efa87241272104d6a12c8b9fcdc4f62634d447
> 
> Yep, a sync of the dma descriptors before the hardware gets ownership of the tx tail
> idx is missing in the stmmac, too. 

Thanks for the hint. Actually, the driver uses smp_wmb() which is
completely crazy, and probably misses rmb() in clean_tx, too. Anyway,
I did not notice there are dma_ variants, too... we clearly need them.

Thanks and best regards,
								Pavel
								
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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