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[PATCH net 0/6] mvneta fixes for SMP

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  [PATCH net 0/6] mvneta fixes for SMP Gregory CLEMENT <gregory.clement@free-electrons.com> - 2016-01-29 17:30 +0100
    [PATCH net 4/6] net: mvneta: Modify the queue related fields from each cpu Gregory CLEMENT <gregory.clement@free-electrons.com> - 2016-01-29 17:30 +0100
    [PATCH net 5/6] net: mvneta: The mvneta_percpu_elect function should be atomic Gregory CLEMENT <gregory.clement@free-electrons.com> - 2016-01-29 17:30 +0100
      Re: [PATCH net 5/6] net: mvneta: The mvneta_percpu_elect function  should be atomic David Miller <davem@davemloft.net> - 2016-01-30 05:40 +0100
        Re: [PATCH net 5/6] net: mvneta: The mvneta_percpu_elect function should be atomic Gregory CLEMENT <gregory.clement@free-electrons.com> - 2016-02-01 11:30 +0100
    [PATCH net 6/6] net: mvneta: Fix race condition during stopping Gregory CLEMENT <gregory.clement@free-electrons.com> - 2016-01-29 17:30 +0100
    [PATCH net 1/6] net: mvneta: Fix for_each_present_cpu usage Gregory CLEMENT <gregory.clement@free-electrons.com> - 2016-01-29 17:30 +0100

#1321864 — [PATCH net 0/6] mvneta fixes for SMP

Hi,

Following this bug report:
http://thread.gmane.org/gmane.linux.ports.arm.kernel/468173 and the
suggestions from Russell King, I reviewed all the code involving
multi-CPU. It ended with this series of patches which should improve
the stability of the driver.

The first patch fix a real bug, the other fix potential issues in the
driver.

Thanks,

Gregory

Gregory CLEMENT (6):
  net: mvneta: Fix for_each_present_cpu usage
  net: mvneta: Use on_each_cpu when possible
  net: mvneta: Remove unused code
  net: mvneta: Modify the queue related fields from each cpu
  net: mvneta: The mvneta_percpu_elect function should be atomic
  net: mvneta: Fix race condition during stopping

 drivers/net/ethernet/marvell/mvneta.c | 160 +++++++++++++++++-----------------
 1 file changed, 82 insertions(+), 78 deletions(-)

-- 
2.5.0

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#1321868 — [PATCH net 4/6] net: mvneta: Modify the queue related fields from each cpu

In the MVNETA_INTR_* registers, the queues related fields are per cpu,
according to the datasheet (comment in [] are added by me):
"In a multi-CPU system, bits of RX[or TX] queues for which the access by
the reading[or writing] CPU is disabled are read as 0, and cannot be
cleared[or written]."

That means that each time we want to manipulate these bits we had to do
it on each cpu and not only on the current cpu.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
---
 drivers/net/ethernet/marvell/mvneta.c | 100 ++++++++++++++++------------------
 1 file changed, 46 insertions(+), 54 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 861b7e0d7d5f..1ed813d478e8 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -1038,6 +1038,43 @@ static void mvneta_set_autoneg(struct mvneta_port *pp, int enable)
 	}
 }
 
+static void mvneta_percpu_unmask_interrupt(void *arg)
+{
+	struct mvneta_port *pp = arg;
+
+	/* All the queue are unmasked, but actually only the ones
+	 * mapped to this CPU will be unmasked
+	 */
+	mvreg_write(pp, MVNETA_INTR_NEW_MASK,
+		    MVNETA_RX_INTR_MASK_ALL |
+		    MVNETA_TX_INTR_MASK_ALL |
+		    MVNETA_MISCINTR_INTR_MASK);
+}
+
+static void mvneta_percpu_mask_interrupt(void *arg)
+{
+	struct mvneta_port *pp = arg;
+
+	/* All the queue are masked, but actually only the ones
+	 * mapped to this CPU will be masked
+	 */
+	mvreg_write(pp, MVNETA_INTR_NEW_MASK, 0);
+	mvreg_write(pp, MVNETA_INTR_OLD_MASK, 0);
+	mvreg_write(pp, MVNETA_INTR_MISC_MASK, 0);
+}
+
+static void mvneta_percpu_clear_intr_cause(void *arg)
+{
+	struct mvneta_port *pp = arg;
+
+	/* All the queue are cleared, but actually only the ones
+	 * mapped to this CPU will be cleared
+	 */
+	mvreg_write(pp, MVNETA_INTR_NEW_CAUSE, 0);
+	mvreg_write(pp, MVNETA_INTR_MISC_CAUSE, 0);
+	mvreg_write(pp, MVNETA_INTR_OLD_CAUSE, 0);
+}
+
 /* This method sets defaults to the NETA port:
  *	Clears interrupt Cause and Mask registers.
  *	Clears all MAC tables.
@@ -1055,14 +1092,10 @@ static void mvneta_defaults_set(struct mvneta_port *pp)
 	int max_cpu = num_present_cpus();
 
 	/* Clear all Cause registers */
-	mvreg_write(pp, MVNETA_INTR_NEW_CAUSE, 0);
-	mvreg_write(pp, MVNETA_INTR_OLD_CAUSE, 0);
-	mvreg_write(pp, MVNETA_INTR_MISC_CAUSE, 0);
+	on_each_cpu(mvneta_percpu_clear_intr_cause, pp, true);
 
 	/* Mask all interrupts */
-	mvreg_write(pp, MVNETA_INTR_NEW_MASK, 0);
-	mvreg_write(pp, MVNETA_INTR_OLD_MASK, 0);
-	mvreg_write(pp, MVNETA_INTR_MISC_MASK, 0);
+	on_each_cpu(mvneta_percpu_mask_interrupt, pp, true);
 	mvreg_write(pp, MVNETA_INTR_ENABLE, 0);
 
 	/* Enable MBUS Retry bit16 */
@@ -2528,31 +2561,6 @@ static int mvneta_setup_txqs(struct mvneta_port *pp)
 	return 0;
 }
 
-static void mvneta_percpu_unmask_interrupt(void *arg)
-{
-	struct mvneta_port *pp = arg;
-
-	/* All the queue are unmasked, but actually only the ones
-	 * maped to this CPU will be unmasked
-	 */
-	mvreg_write(pp, MVNETA_INTR_NEW_MASK,
-		    MVNETA_RX_INTR_MASK_ALL |
-		    MVNETA_TX_INTR_MASK_ALL |
-		    MVNETA_MISCINTR_INTR_MASK);
-}
-
-static void mvneta_percpu_mask_interrupt(void *arg)
-{
-	struct mvneta_port *pp = arg;
-
-	/* All the queue are masked, but actually only the ones
-	 * maped to this CPU will be masked
-	 */
-	mvreg_write(pp, MVNETA_INTR_NEW_MASK, 0);
-	mvreg_write(pp, MVNETA_INTR_OLD_MASK, 0);
-	mvreg_write(pp, MVNETA_INTR_MISC_MASK, 0);
-}
-
 static void mvneta_start_dev(struct mvneta_port *pp)
 {
 	int cpu;
@@ -2603,13 +2611,10 @@ static void mvneta_stop_dev(struct mvneta_port *pp)
 	mvneta_port_disable(pp);
 
 	/* Clear all ethernet port interrupts */
-	mvreg_write(pp, MVNETA_INTR_MISC_CAUSE, 0);
-	mvreg_write(pp, MVNETA_INTR_OLD_CAUSE, 0);
+	on_each_cpu(mvneta_percpu_clear_intr_cause, pp, true);
 
 	/* Mask all ethernet port interrupts */
-	mvreg_write(pp, MVNETA_INTR_NEW_MASK, 0);
-	mvreg_write(pp, MVNETA_INTR_OLD_MASK, 0);
-	mvreg_write(pp, MVNETA_INTR_MISC_MASK, 0);
+	on_each_cpu(mvneta_percpu_mask_interrupt, pp, true);
 
 	mvneta_tx_reset(pp);
 	mvneta_rx_reset(pp);
@@ -2916,9 +2921,7 @@ static int mvneta_percpu_notifier(struct notifier_block *nfb,
 		}
 
 		/* Mask all ethernet port interrupts */
-		mvreg_write(pp, MVNETA_INTR_NEW_MASK, 0);
-		mvreg_write(pp, MVNETA_INTR_OLD_MASK, 0);
-		mvreg_write(pp, MVNETA_INTR_MISC_MASK, 0);
+		on_each_cpu(mvneta_percpu_mask_interrupt, pp, true);
 		napi_enable(&port->napi);
 
 
@@ -2933,14 +2936,8 @@ static int mvneta_percpu_notifier(struct notifier_block *nfb,
 		 */
 		mvneta_percpu_elect(pp);
 
-		/* Unmask all ethernet port interrupts, as this
-		 * notifier is called for each CPU then the CPU to
-		 * Queue mapping is applied
-		 */
-		mvreg_write(pp, MVNETA_INTR_NEW_MASK,
-			MVNETA_RX_INTR_MASK(rxq_number) |
-			MVNETA_TX_INTR_MASK(txq_number) |
-			MVNETA_MISCINTR_INTR_MASK);
+		/* Unmask all ethernet port interrupts */
+		on_each_cpu(mvneta_percpu_unmask_interrupt, pp, true);
 		mvreg_write(pp, MVNETA_INTR_MISC_MASK,
 			MVNETA_CAUSE_PHY_STATUS_CHANGE |
 			MVNETA_CAUSE_LINK_CHANGE |
@@ -2951,9 +2948,7 @@ static int mvneta_percpu_notifier(struct notifier_block *nfb,
 	case CPU_DOWN_PREPARE_FROZEN:
 		netif_tx_stop_all_queues(pp->dev);
 		/* Mask all ethernet port interrupts */
-		mvreg_write(pp, MVNETA_INTR_NEW_MASK, 0);
-		mvreg_write(pp, MVNETA_INTR_OLD_MASK, 0);
-		mvreg_write(pp, MVNETA_INTR_MISC_MASK, 0);
+		on_each_cpu(mvneta_percpu_mask_interrupt, pp, true);
 
 		napi_synchronize(&port->napi);
 		napi_disable(&port->napi);
@@ -2969,10 +2964,7 @@ static int mvneta_percpu_notifier(struct notifier_block *nfb,
 		/* Check if a new CPU must be elected now this on is down */
 		mvneta_percpu_elect(pp);
 		/* Unmask all ethernet port interrupts */
-		mvreg_write(pp, MVNETA_INTR_NEW_MASK,
-			MVNETA_RX_INTR_MASK(rxq_number) |
-			MVNETA_TX_INTR_MASK(txq_number) |
-			MVNETA_MISCINTR_INTR_MASK);
+		on_each_cpu(mvneta_percpu_unmask_interrupt, pp, true);
 		mvreg_write(pp, MVNETA_INTR_MISC_MASK,
 			MVNETA_CAUSE_PHY_STATUS_CHANGE |
 			MVNETA_CAUSE_LINK_CHANGE |
-- 
2.5.0

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#1321872 — [PATCH net 5/6] net: mvneta: The mvneta_percpu_elect function should be atomic

Electing a CPU must be done in an atomic way: it should be done after or
before the removal/insertion of a CPU and this function is not reentrant.

During the loop of mvneta_percpu_elect we associates the queues to the
CPUs, if there is a topology change during this loop, then the mapping
between the CPUs and the queues could be wrong. During this loop the
interrupt mask is also updating for each CPUs, It should not be changed
in the same time by other part of the driver.

This patch adds spinlock to create the needed critical sections.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
---
 drivers/net/ethernet/marvell/mvneta.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 1ed813d478e8..3358c9a70467 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -370,6 +370,8 @@ struct mvneta_port {
 	struct net_device *dev;
 	struct notifier_block cpu_notifier;
 	int rxq_def;
+	/* protect  */
+	spinlock_t lock;
 
 	/* Core clock */
 	struct clk *clk;
@@ -2855,6 +2857,11 @@ static void mvneta_percpu_elect(struct mvneta_port *pp)
 {
 	int online_cpu_idx, max_cpu, cpu, i = 0;
 
+	/* Electing a CPU must done in an atomic way: it should be
+	 * done after or before the removal/insertion of a CPU and
+	 * this function is not reentrant.
+	 */
+	spin_lock(&pp->lock);
 	online_cpu_idx = pp->rxq_def % num_online_cpus();
 	max_cpu = num_present_cpus();
 
@@ -2893,6 +2900,7 @@ static void mvneta_percpu_elect(struct mvneta_port *pp)
 		i++;
 
 	}
+	spin_unlock(&pp->lock);
 };
 
 static int mvneta_percpu_notifier(struct notifier_block *nfb,
@@ -2947,8 +2955,13 @@ static int mvneta_percpu_notifier(struct notifier_block *nfb,
 	case CPU_DOWN_PREPARE:
 	case CPU_DOWN_PREPARE_FROZEN:
 		netif_tx_stop_all_queues(pp->dev);
+		/* Thanks to this lock we are sure that any pending
+		 * cpu election is done
+		 */
+		spin_lock(&pp->lock);
 		/* Mask all ethernet port interrupts */
 		on_each_cpu(mvneta_percpu_mask_interrupt, pp, true);
+		spin_unlock(&pp->lock);
 
 		napi_synchronize(&port->napi);
 		napi_disable(&port->napi);
-- 
2.5.0

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#1322258 — Re: [PATCH net 5/6] net: mvneta: The mvneta_percpu_elect function should be atomic

From: Gregory CLEMENT <gregory.clement@free-electrons.com>
Date: Fri, 29 Jan 2016 17:26:06 +0100

> @@ -370,6 +370,8 @@ struct mvneta_port {
>  	struct net_device *dev;
>  	struct notifier_block cpu_notifier;
>  	int rxq_def;
> +	/* protect  */
> +	spinlock_t lock;
>  
>  	/* Core clock */
>  	struct clk *clk;

Protect what?  This comment needs a lot of improvement.

Everyone knows a spinlock "protects" things, so if you aren't going
to actually describe what this lock protects, and in what contexts
the lock is used, you might as well not say anything at all.

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#1322974 — Re: [PATCH net 5/6] net: mvneta: The mvneta_percpu_elect function should be atomic

Hi David,
 
 On sam., janv. 30 2016, David Miller <davem@davemloft.net> wrote:

> From: Gregory CLEMENT <gregory.clement@free-electrons.com>
> Date: Fri, 29 Jan 2016 17:26:06 +0100
>
>> @@ -370,6 +370,8 @@ struct mvneta_port {
>>  	struct net_device *dev;
>>  	struct notifier_block cpu_notifier;
>>  	int rxq_def;
>> +	/* protect  */
>> +	spinlock_t lock;
>>  
>>  	/* Core clock */
>>  	struct clk *clk;
>
> Protect what?  This comment needs a lot of improvement.

Sorry about it, this was a left-over.

>
> Everyone knows a spinlock "protects" things, so if you aren't going
> to actually describe what this lock protects, and in what contexts
> the lock is used, you might as well not say anything at all.

I can only agree with you, I will fix it for next version.

Thanks,

Gregory


-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com

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#1321873 — [PATCH net 6/6] net: mvneta: Fix race condition during stopping

When stopping the port, the CPU notifier are still there whereas the
mvneta_stop_dev function calls mvneta_percpu_disable() on each CPUs.
It was possible to have a new CPU coming at this point which could be
racy.

This patch adds a flag preventing executing the code notifier for a new CPU
when the port is stopping.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
---
 drivers/net/ethernet/marvell/mvneta.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 3358c9a70467..22962fac47c2 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -372,6 +372,7 @@ struct mvneta_port {
 	int rxq_def;
 	/* protect  */
 	spinlock_t lock;
+	bool is_stopping;
 
 	/* Core clock */
 	struct clk *clk;
@@ -2914,6 +2915,11 @@ static int mvneta_percpu_notifier(struct notifier_block *nfb,
 	switch (action) {
 	case CPU_ONLINE:
 	case CPU_ONLINE_FROZEN:
+		/* Configuring the driver for a new CPU while the
+		 * driver is stopping is racy, so just avoid it.
+		 */
+		if (pp->is_stopping)
+			break;
 		netif_tx_stop_all_queues(pp->dev);
 
 		/* We have to synchronise on tha napi of each CPU
@@ -3052,9 +3058,17 @@ static int mvneta_stop(struct net_device *dev)
 {
 	struct mvneta_port *pp = netdev_priv(dev);
 
+	/* Inform that we are stopping so we don't want to setup the
+	 * driver for new CPUs in the notifiers
+	 */
+	pp->is_stopping = true;
 	mvneta_stop_dev(pp);
 	mvneta_mdio_remove(pp);
 	unregister_cpu_notifier(&pp->cpu_notifier);
+	/* Now that the notifier are unregistered, we can clear the
+	 * flag
+	 */
+	pp->is_stopping = false;
 	on_each_cpu(mvneta_percpu_disable, pp, true);
 	free_percpu_irq(dev->irq, pp->ports);
 	mvneta_cleanup_rxqs(pp);
-- 
2.5.0

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#1321874 — [PATCH net 1/6] net: mvneta: Fix for_each_present_cpu usage

This patch convert the for_each_present in on_each_cpu, instead of
applying on the present cpus it will be applied only on the online cpus.
This fix a bug reported on
http://thread.gmane.org/gmane.linux.ports.arm.kernel/468173.

Using the macro on_each_cpu (instead of a for_each_* loop) also ensures
that all the calls will be done all at once.

Fixes: f86428854480 ("net: mvneta: Statically assign queues to CPUs")
Reported-by: Stefan Roese <stefan.roese@gmail.com>
Suggested-by: Jisheng Zhang <jszhang@marvell.com>
Suggested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
---
 drivers/net/ethernet/marvell/mvneta.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 662c2ee268c7..90ff5c7e19ea 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -2564,7 +2564,7 @@ static void mvneta_start_dev(struct mvneta_port *pp)
 	mvneta_port_enable(pp);
 
 	/* Enable polling on the port */
-	for_each_present_cpu(cpu) {
+	for_each_online_cpu(cpu) {
 		struct mvneta_pcpu_port *port = per_cpu_ptr(pp->ports, cpu);
 
 		napi_enable(&port->napi);
@@ -2589,7 +2589,7 @@ static void mvneta_stop_dev(struct mvneta_port *pp)
 
 	phy_stop(pp->phy_dev);
 
-	for_each_present_cpu(cpu) {
+	for_each_online_cpu(cpu) {
 		struct mvneta_pcpu_port *port = per_cpu_ptr(pp->ports, cpu);
 
 		napi_disable(&port->napi);
@@ -3057,13 +3057,11 @@ err_cleanup_rxqs:
 static int mvneta_stop(struct net_device *dev)
 {
 	struct mvneta_port *pp = netdev_priv(dev);
-	int cpu;
 
 	mvneta_stop_dev(pp);
 	mvneta_mdio_remove(pp);
 	unregister_cpu_notifier(&pp->cpu_notifier);
-	for_each_present_cpu(cpu)
-		smp_call_function_single(cpu, mvneta_percpu_disable, pp, true);
+	on_each_cpu(mvneta_percpu_disable, pp, true);
 	free_percpu_irq(dev->irq, pp->ports);
 	mvneta_cleanup_rxqs(pp);
 	mvneta_cleanup_txqs(pp);
-- 
2.5.0

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