[PATCH 50/51] net/core/flow.c: Fix CPU hotplug callback registration

[PATCH 50/51] net/core/flow.c: Fix CPU hotplug callback registration

[Srivatsa S. Bhat]

Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	register_cpu_notifier(&foobar_cpu_notifier);

	put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

	cpu_maps_update_begin();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	/* Note the use of the double underscored version of the API */
	__register_cpu_notifier(&foobar_cpu_notifier);

	cpu_maps_update_done();


Fix the code in net/core/flow.c by using this latter form of callback
registration.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Li RongQing <roy.qing.li@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: netdev@vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

 net/core/flow.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/core/flow.c b/net/core/flow.c
index dfa602c..0f2c995 100644
--- a/net/core/flow.c
+++ b/net/core/flow.c
@@ -456,6 +456,8 @@ static int __init flow_cache_init(struct flow_cache *fc)
 	if (!fc->percpu)
 		return -ENOMEM;
 
+	cpu_maps_update_begin();
+
 	for_each_online_cpu(i) {
 		if (flow_cache_cpu_prepare(fc, i))
 			goto err;
@@ -463,7 +465,9 @@ static int __init flow_cache_init(struct flow_cache *fc)
 	fc->hotcpu_notifier = (struct notifier_block){
 		.notifier_call = flow_cache_cpu,
 	};
-	register_hotcpu_notifier(&fc->hotcpu_notifier);
+	__register_hotcpu_notifier(&fc->hotcpu_notifier);
+
+	cpu_maps_update_done();
 
 	setup_timer(&fc->rnd_timer, flow_cache_new_hashrnd,
 		    (unsigned long) fc);
@@ -479,6 +483,8 @@ err:
 		fcp->hash_table = NULL;
 	}
 
+	cpu_maps_update_done();
+
 	free_percpu(fc->percpu);
 	fc->percpu = NULL;
 

[PATCH 51/51] net/iucv/iucv.c: Fix CPU hotplug callback registration

[Srivatsa S. Bhat]

Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	register_cpu_notifier(&foobar_cpu_notifier);

	put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

	cpu_maps_update_begin();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	/* Note the use of the double underscored version of the API */
	__register_cpu_notifier(&foobar_cpu_notifier);

	cpu_maps_update_done();


Fix the code in net/iucv/iucv.c by using this latter form of callback
registration. Also, provide helper functions to perform the common memory
allocations and frees, to condense repetitive code.

Cc: Ursula Braun <ursula.braun@de.ibm.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-s390@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

 net/iucv/iucv.c |  121 ++++++++++++++++++++++++++-----------------------------
 1 file changed, 57 insertions(+), 64 deletions(-)

diff --git a/net/iucv/iucv.c b/net/iucv/iucv.c
index cd5b8ec..f92348b 100644
--- a/net/iucv/iucv.c
+++ b/net/iucv/iucv.c
@@ -621,6 +621,42 @@ static void iucv_disable(void)
 	put_online_cpus();
 }
 
+static void free_iucv_data(int cpu)
+{
+	kfree(iucv_param_irq[cpu]);
+	iucv_param_irq[cpu] = NULL;
+	kfree(iucv_param[cpu]);
+	iucv_param[cpu] = NULL;
+	kfree(iucv_irq_data[cpu]);
+	iucv_irq_data[cpu] = NULL;
+}
+
+static int alloc_iucv_data(int cpu)
+{
+	/* Note: GFP_DMA used to get memory below 2G */
+	iucv_irq_data[cpu] = kmalloc_node(sizeof(struct iucv_irq_data),
+			     GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
+	if (!iucv_irq_data[cpu])
+		goto out_free;
+
+	/* Allocate parameter blocks. */
+	iucv_param[cpu] = kmalloc_node(sizeof(union iucv_param),
+			  GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
+	if (!iucv_param[cpu])
+		goto out_free;
+
+	iucv_param_irq[cpu] = kmalloc_node(sizeof(union iucv_param),
+			  GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
+	if (!iucv_param_irq[cpu])
+		goto out_free;
+
+	return 0;
+
+out_free:
+	free_iucv_data(cpu);
+	return -ENOMEM;
+}
+
 static int iucv_cpu_notify(struct notifier_block *self,
 				     unsigned long action, void *hcpu)
 {
@@ -630,38 +666,14 @@ static int iucv_cpu_notify(struct notifier_block *self,
 	switch (action) {
 	case CPU_UP_PREPARE:
 	case CPU_UP_PREPARE_FROZEN:
-		iucv_irq_data[cpu] = kmalloc_node(sizeof(struct iucv_irq_data),
-					GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
-		if (!iucv_irq_data[cpu])
-			return notifier_from_errno(-ENOMEM);
-
-		iucv_param[cpu] = kmalloc_node(sizeof(union iucv_param),
-				     GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
-		if (!iucv_param[cpu]) {
-			kfree(iucv_irq_data[cpu]);
-			iucv_irq_data[cpu] = NULL;
+		if (alloc_iucv_data(cpu))
 			return notifier_from_errno(-ENOMEM);
-		}
-		iucv_param_irq[cpu] = kmalloc_node(sizeof(union iucv_param),
-					GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
-		if (!iucv_param_irq[cpu]) {
-			kfree(iucv_param[cpu]);
-			iucv_param[cpu] = NULL;
-			kfree(iucv_irq_data[cpu]);
-			iucv_irq_data[cpu] = NULL;
-			return notifier_from_errno(-ENOMEM);
-		}
 		break;
 	case CPU_UP_CANCELED:
 	case CPU_UP_CANCELED_FROZEN:
 	case CPU_DEAD:
 	case CPU_DEAD_FROZEN:
-		kfree(iucv_param_irq[cpu]);
-		iucv_param_irq[cpu] = NULL;
-		kfree(iucv_param[cpu]);
-		iucv_param[cpu] = NULL;
-		kfree(iucv_irq_data[cpu]);
-		iucv_irq_data[cpu] = NULL;
+		free_iucv_data(cpu);
 		break;
 	case CPU_ONLINE:
 	case CPU_ONLINE_FROZEN:
@@ -2025,33 +2037,20 @@ static int __init iucv_init(void)
 		goto out_int;
 	}
 
-	for_each_online_cpu(cpu) {
-		/* Note: GFP_DMA used to get memory below 2G */
-		iucv_irq_data[cpu] = kmalloc_node(sizeof(struct iucv_irq_data),
-				     GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
-		if (!iucv_irq_data[cpu]) {
-			rc = -ENOMEM;
-			goto out_free;
-		}
+	cpu_maps_update_begin();
 
-		/* Allocate parameter blocks. */
-		iucv_param[cpu] = kmalloc_node(sizeof(union iucv_param),
-				  GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
-		if (!iucv_param[cpu]) {
-			rc = -ENOMEM;
-			goto out_free;
-		}
-		iucv_param_irq[cpu] = kmalloc_node(sizeof(union iucv_param),
-				  GFP_KERNEL|GFP_DMA, cpu_to_node(cpu));
-		if (!iucv_param_irq[cpu]) {
+	for_each_online_cpu(cpu) {
+		if (alloc_iucv_data(cpu)) {
 			rc = -ENOMEM;
 			goto out_free;
 		}
-
 	}
-	rc = register_hotcpu_notifier(&iucv_cpu_notifier);
+	rc = __register_hotcpu_notifier(&iucv_cpu_notifier);
 	if (rc)
 		goto out_free;
+
+	cpu_maps_update_done();
+
 	rc = register_reboot_notifier(&iucv_reboot_notifier);
 	if (rc)
 		goto out_cpu;
@@ -2069,16 +2068,14 @@ static int __init iucv_init(void)
 out_reboot:
 	unregister_reboot_notifier(&iucv_reboot_notifier);
 out_cpu:
-	unregister_hotcpu_notifier(&iucv_cpu_notifier);
+	cpu_maps_update_begin();
+	__unregister_hotcpu_notifier(&iucv_cpu_notifier);
 out_free:
-	for_each_possible_cpu(cpu) {
-		kfree(iucv_param_irq[cpu]);
-		iucv_param_irq[cpu] = NULL;
-		kfree(iucv_param[cpu]);
-		iucv_param[cpu] = NULL;
-		kfree(iucv_irq_data[cpu]);
-		iucv_irq_data[cpu] = NULL;
-	}
+	for_each_possible_cpu(cpu)
+		free_iucv_data(cpu);
+
+	cpu_maps_update_done();
+
 	root_device_unregister(iucv_root);
 out_int:
 	unregister_external_interrupt(0x4000, iucv_external_interrupt);
@@ -2105,15 +2102,11 @@ static void __exit iucv_exit(void)
 		kfree(p);
 	spin_unlock_irq(&iucv_queue_lock);
 	unregister_reboot_notifier(&iucv_reboot_notifier);
-	unregister_hotcpu_notifier(&iucv_cpu_notifier);
-	for_each_possible_cpu(cpu) {
-		kfree(iucv_param_irq[cpu]);
-		iucv_param_irq[cpu] = NULL;
-		kfree(iucv_param[cpu]);
-		iucv_param[cpu] = NULL;
-		kfree(iucv_irq_data[cpu]);
-		iucv_irq_data[cpu] = NULL;
-	}
+	cpu_maps_update_begin();
+	__unregister_hotcpu_notifier(&iucv_cpu_notifier);
+	for_each_possible_cpu(cpu)
+		free_iucv_data(cpu);
+	cpu_maps_update_done();
 	root_device_unregister(iucv_root);
 	bus_unregister(&iucv_bus);
 	unregister_external_interrupt(0x4000, iucv_external_interrupt);

Re: [PATCH 50/51] net/core/flow.c: Fix CPU hotplug callback registration

[David Miller]

From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Date: Thu, 06 Feb 2014 03:43:46 +0530

> Subsystems that want to register CPU hotplug callbacks, as well as perform
> initialization for the CPUs that are already online, often do it as shown
> below:
 ...
> This is wrong, since it is prone to ABBA deadlocks involving the
> cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
> with CPU hotplug operations).
> 
> Instead, the correct and race-free way of performing the callback
> registration is:
 ...
> Fix the code in net/core/flow.c by using this latter form of callback
> registration.
> 
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Li RongQing <roy.qing.li@gmail.com>
> Cc: Sasha Levin <sasha.levin@oracle.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Chris Metcalf <cmetcalf@tilera.com>
> Cc: netdev@vger.kernel.org
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

Applied.

Re: [PATCH 51/51] net/iucv/iucv.c: Fix CPU hotplug callback registration

[David Miller]

From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Date: Thu, 06 Feb 2014 03:43:55 +0530

> Subsystems that want to register CPU hotplug callbacks, as well as perform
> initialization for the CPUs that are already online, often do it as shown
> below:
 ...
> This is wrong, since it is prone to ABBA deadlocks involving the
> cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
> with CPU hotplug operations).
> 
> Instead, the correct and race-free way of performing the callback
> registration is:
 ...
> Fix the code in net/iucv/iucv.c by using this latter form of callback
> registration. Also, provide helper functions to perform the common memory
> allocations and frees, to condense repetitive code.
> 
> Cc: Ursula Braun <ursula.braun@de.ibm.com>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: linux-s390@vger.kernel.org
> Cc: netdev@vger.kernel.org
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

Applied.

Re: [PATCH 51/51] net/iucv/iucv.c: Fix CPU hotplug callback registration

[David Miller]

From: David Miller <davem@davemloft.net>
Date: Thu, 06 Feb 2014 20:39:35 -0800 (PST)

> Applied.

I just realized that this has a dependency not in the 'net'
tree, so I reverted and assume you will merge this with the
patch that provides the necessary interface(s).

Signed-off-by: David S. Miller <davem@davemloft.net>

Re: [PATCH 50/51] net/core/flow.c: Fix CPU hotplug callback registration

[David Miller]

From: David Miller <davem@davemloft.net>
Date: Thu, 06 Feb 2014 20:39:21 -0800 (PST)

> From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
> Date: Thu, 06 Feb 2014 03:43:46 +0530
> 
>> Subsystems that want to register CPU hotplug callbacks, as well as perform
>> initialization for the CPUs that are already online, often do it as shown
>> below:
>  ...
>> This is wrong, since it is prone to ABBA deadlocks involving the
>> cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
>> with CPU hotplug operations).
>> 
>> Instead, the correct and race-free way of performing the callback
>> registration is:
>  ...
>> Fix the code in net/core/flow.c by using this latter form of callback
>> registration.
>> 
>> Cc: "David S. Miller" <davem@davemloft.net>
>> Cc: Li RongQing <roy.qing.li@gmail.com>
>> Cc: Sasha Levin <sasha.levin@oracle.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Chris Metcalf <cmetcalf@tilera.com>
>> Cc: netdev@vger.kernel.org
>> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> 
> Applied.

I just realized that this has a dependency not in the 'net'
tree, so I reverted and assume you will merge this with the
patch that provides the necessary interface(s).

Signed-off-by: David S. Miller <davem@davemloft.net>