diff mbox

mm/hotplug: Remove stop_machine() from try_offline_node()

Message ID 1376336071-9128-1-git-send-email-toshi.kani@hp.com (mailing list archive)
State Not Applicable, archived
Headers show

Commit Message

Toshi Kani Aug. 12, 2013, 7:34 p.m. UTC 
lock_device_hotplug() serializes hotplug & online/offline operations.
The lock is held in common sysfs online/offline interfaces and ACPI
hotplug code paths.

try_offline_node() off-lines a node if all memory sections and cpus
are removed on the node.  It is called from acpi_processor_remove()
and acpi_memory_remove_memory()->remove_memory() paths, both of which
are in the ACPI hotplug code.

try_offline_node() calls stop_machine() to stop all cpus while checking
all cpu status with the assumption that the caller is not protected from
CPU hotplug or CPU online/offline operations.  However, the caller is
always serialized with lock_device_hotplug().  Also, the code needs to
be properly serialized with a lock, not by stopping all cpus at a random
place with stop_machine().

This patch removes the use of stop_machine() in try_offline_node() and
adds comments to try_offline_node() and remove_memory() that
lock_device_hotplug() is required.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
---
 mm/memory_hotplug.c |   31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

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Comments

Rafael Wysocki Aug. 13, 2013, 11:41 a.m. UTC | #1 
On Monday, August 12, 2013 01:34:31 PM Toshi Kani wrote:
> lock_device_hotplug() serializes hotplug & online/offline operations.
> The lock is held in common sysfs online/offline interfaces and ACPI
> hotplug code paths.
> 
> try_offline_node() off-lines a node if all memory sections and cpus
> are removed on the node.  It is called from acpi_processor_remove()
> and acpi_memory_remove_memory()->remove_memory() paths, both of which
> are in the ACPI hotplug code.
> 
> try_offline_node() calls stop_machine() to stop all cpus while checking
> all cpu status with the assumption that the caller is not protected from
> CPU hotplug or CPU online/offline operations.  However, the caller is
> always serialized with lock_device_hotplug().  Also, the code needs to
> be properly serialized with a lock, not by stopping all cpus at a random
> place with stop_machine().
> 
> This patch removes the use of stop_machine() in try_offline_node() and
> adds comments to try_offline_node() and remove_memory() that
> lock_device_hotplug() is required.
> 
> Signed-off-by: Toshi Kani <toshi.kani@hp.com>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
>  mm/memory_hotplug.c |   31 ++++++++++++++++++++++---------
>  1 file changed, 22 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index ca1dd3a..0b4b0f7 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1674,9 +1674,8 @@ static int is_memblock_offlined_cb(struct memory_block *mem, void *arg)
>  	return ret;
>  }
>  
> -static int check_cpu_on_node(void *data)
> +static int check_cpu_on_node(pg_data_t *pgdat)
>  {
> -	struct pglist_data *pgdat = data;
>  	int cpu;
>  
>  	for_each_present_cpu(cpu) {
> @@ -1691,10 +1690,9 @@ static int check_cpu_on_node(void *data)
>  	return 0;
>  }
>  
> -static void unmap_cpu_on_node(void *data)
> +static void unmap_cpu_on_node(pg_data_t *pgdat)
>  {
>  #ifdef CONFIG_ACPI_NUMA
> -	struct pglist_data *pgdat = data;
>  	int cpu;
>  
>  	for_each_possible_cpu(cpu)
> @@ -1703,10 +1701,11 @@ static void unmap_cpu_on_node(void *data)
>  #endif
>  }
>  
> -static int check_and_unmap_cpu_on_node(void *data)
> +static int check_and_unmap_cpu_on_node(pg_data_t *pgdat)
>  {
> -	int ret = check_cpu_on_node(data);
> +	int ret;
>  
> +	ret = check_cpu_on_node(pgdat);
>  	if (ret)
>  		return ret;
>  
> @@ -1715,11 +1714,18 @@ static int check_and_unmap_cpu_on_node(void *data)
>  	 * the cpu_to_node() now.
>  	 */
>  
> -	unmap_cpu_on_node(data);
> +	unmap_cpu_on_node(pgdat);
>  	return 0;
>  }
>  
> -/* offline the node if all memory sections of this node are removed */
> +/**
> + * try_offline_node
> + *
> + * Offline a node if all memory sections and cpus of the node are removed.
> + *
> + * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
> + * and online/offline operations before this call.
> + */
>  void try_offline_node(int nid)
>  {
>  	pg_data_t *pgdat = NODE_DATA(nid);
> @@ -1745,7 +1751,7 @@ void try_offline_node(int nid)
>  		return;
>  	}
>  
> -	if (stop_machine(check_and_unmap_cpu_on_node, pgdat, NULL))
> +	if (check_and_unmap_cpu_on_node(pgdat))
>  		return;
>  
>  	/*
> @@ -1782,6 +1788,13 @@ void try_offline_node(int nid)
>  }
>  EXPORT_SYMBOL(try_offline_node);
>  
> +/**
> + * remove_memory
> + *
> + * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
> + * and online/offline operations before this call, as required by
> + * try_offline_node().
> + */
>  void __ref remove_memory(int nid, u64 start, u64 size)
>  {
>  	int ret;
Toshi Kani Aug. 13, 2013, 2:44 p.m. UTC | #2 
On Tue, 2013-08-13 at 13:41 +0200, Rafael J. Wysocki wrote:
> On Monday, August 12, 2013 01:34:31 PM Toshi Kani wrote:
> > lock_device_hotplug() serializes hotplug & online/offline operations.
> > The lock is held in common sysfs online/offline interfaces and ACPI
> > hotplug code paths.
> > 
> > try_offline_node() off-lines a node if all memory sections and cpus
> > are removed on the node.  It is called from acpi_processor_remove()
> > and acpi_memory_remove_memory()->remove_memory() paths, both of which
> > are in the ACPI hotplug code.
> > 
> > try_offline_node() calls stop_machine() to stop all cpus while checking
> > all cpu status with the assumption that the caller is not protected from
> > CPU hotplug or CPU online/offline operations.  However, the caller is
> > always serialized with lock_device_hotplug().  Also, the code needs to
> > be properly serialized with a lock, not by stopping all cpus at a random
> > place with stop_machine().
> > 
> > This patch removes the use of stop_machine() in try_offline_node() and
> > adds comments to try_offline_node() and remove_memory() that
> > lock_device_hotplug() is required.
> > 
> > Signed-off-by: Toshi Kani <toshi.kani@hp.com>
> 
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Thanks!
-Toshi


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Motohiro KOSAKI Aug. 15, 2013, 1:21 a.m. UTC | #3 
(8/12/13 3:34 PM), Toshi Kani wrote:
> lock_device_hotplug() serializes hotplug & online/offline operations.
> The lock is held in common sysfs online/offline interfaces and ACPI
> hotplug code paths.
> 
> try_offline_node() off-lines a node if all memory sections and cpus
> are removed on the node.  It is called from acpi_processor_remove()
> and acpi_memory_remove_memory()->remove_memory() paths, both of which
> are in the ACPI hotplug code.
> 
> try_offline_node() calls stop_machine() to stop all cpus while checking
> all cpu status with the assumption that the caller is not protected from
> CPU hotplug or CPU online/offline operations.  However, the caller is
> always serialized with lock_device_hotplug().  Also, the code needs to
> be properly serialized with a lock, not by stopping all cpus at a random
> place with stop_machine().
> 
> This patch removes the use of stop_machine() in try_offline_node() and
> adds comments to try_offline_node() and remove_memory() that
> lock_device_hotplug() is required.

This patch need more verbose explanation. check_cpu_on_node() traverse cpus
and cpu hotplug seems to use cpu_hotplug_driver_lock() instead of lock_device_hotplug().

That said, the race is not happen against another memeory happen. It's likely happen
another cpu hotplug. So commenting remove_memory() doesn't make much sense.

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Toshi Kani Aug. 15, 2013, 4:35 p.m. UTC | #4 
On Wed, 2013-08-14 at 21:21 -0400, KOSAKI Motohiro wrote:
> (8/12/13 3:34 PM), Toshi Kani wrote:
> > lock_device_hotplug() serializes hotplug & online/offline operations.
> > The lock is held in common sysfs online/offline interfaces and ACPI
> > hotplug code paths.
> > 
> > try_offline_node() off-lines a node if all memory sections and cpus
> > are removed on the node.  It is called from acpi_processor_remove()
> > and acpi_memory_remove_memory()->remove_memory() paths, both of which
> > are in the ACPI hotplug code.
> > 
> > try_offline_node() calls stop_machine() to stop all cpus while checking
> > all cpu status with the assumption that the caller is not protected from
> > CPU hotplug or CPU online/offline operations.  However, the caller is
> > always serialized with lock_device_hotplug().  Also, the code needs to
> > be properly serialized with a lock, not by stopping all cpus at a random
> > place with stop_machine().
> > 
> > This patch removes the use of stop_machine() in try_offline_node() and
> > adds comments to try_offline_node() and remove_memory() that
> > lock_device_hotplug() is required.
> 
> This patch need more verbose explanation. check_cpu_on_node() traverse cpus
> and cpu hotplug seems to use cpu_hotplug_driver_lock() instead of lock_device_hotplug().

As described: 

| lock_device_hotplug() serializes hotplug & online/offline operations.
| The lock is held in common sysfs online/offline interfaces and ACPI
| hotplug code paths.

And here are their code paths.

- CPU & Mem online/offline via sysfs online
	store_online()->lock_device_hotplug()

- Mem online via sysfs state:
	store_mem_state()->lock_device_hotplug()

- ACPI CPU & Mem hot-add:
	acpi_scan_bus_device_check()->lock_device_hotplug()

- ACPI CPU & Mem hot-delete:
	acpi_scan_hot_remove()->lock_device_hotplug()

> That said, the race is not happen against another memeory happen. It's likely happen
> another cpu hotplug. So commenting remove_memory() doesn't make much sense.

This lock scheme protects from both CPU and memory hotplug, and requires
the caller to call lock_device_hotplug().

Thanks,
-Toshi


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Motohiro KOSAKI Aug. 16, 2013, 8:31 p.m. UTC | #5 
>>> This patch removes the use of stop_machine() in try_offline_node() and
>>> adds comments to try_offline_node() and remove_memory() that
>>> lock_device_hotplug() is required.
>>
>> This patch need more verbose explanation. check_cpu_on_node() traverse cpus
>> and cpu hotplug seems to use cpu_hotplug_driver_lock() instead of lock_device_hotplug().
>
> As described:
>
> | lock_device_hotplug() serializes hotplug & online/offline operations.
> | The lock is held in common sysfs online/offline interfaces and ACPI
> | hotplug code paths.
>
> And here are their code paths.
>
> - CPU & Mem online/offline via sysfs online
> 	store_online()->lock_device_hotplug()
>
> - Mem online via sysfs state:
> 	store_mem_state()->lock_device_hotplug()
>
> - ACPI CPU & Mem hot-add:
> 	acpi_scan_bus_device_check()->lock_device_hotplug()
>
> - ACPI CPU & Mem hot-delete:
> 	acpi_scan_hot_remove()->lock_device_hotplug()

O.K.


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diff mbox

Patch

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index ca1dd3a..0b4b0f7 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1674,9 +1674,8 @@  static int is_memblock_offlined_cb(struct memory_block *mem, void *arg)
 	return ret;
 }
 
-static int check_cpu_on_node(void *data)
+static int check_cpu_on_node(pg_data_t *pgdat)
 {
-	struct pglist_data *pgdat = data;
 	int cpu;
 
 	for_each_present_cpu(cpu) {
@@ -1691,10 +1690,9 @@  static int check_cpu_on_node(void *data)
 	return 0;
 }
 
-static void unmap_cpu_on_node(void *data)
+static void unmap_cpu_on_node(pg_data_t *pgdat)
 {
 #ifdef CONFIG_ACPI_NUMA
-	struct pglist_data *pgdat = data;
 	int cpu;
 
 	for_each_possible_cpu(cpu)
@@ -1703,10 +1701,11 @@  static void unmap_cpu_on_node(void *data)
 #endif
 }
 
-static int check_and_unmap_cpu_on_node(void *data)
+static int check_and_unmap_cpu_on_node(pg_data_t *pgdat)
 {
-	int ret = check_cpu_on_node(data);
+	int ret;
 
+	ret = check_cpu_on_node(pgdat);
 	if (ret)
 		return ret;
 
@@ -1715,11 +1714,18 @@  static int check_and_unmap_cpu_on_node(void *data)
 	 * the cpu_to_node() now.
 	 */
 
-	unmap_cpu_on_node(data);
+	unmap_cpu_on_node(pgdat);
 	return 0;
 }
 
-/* offline the node if all memory sections of this node are removed */
+/**
+ * try_offline_node
+ *
+ * Offline a node if all memory sections and cpus of the node are removed.
+ *
+ * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
+ * and online/offline operations before this call.
+ */
 void try_offline_node(int nid)
 {
 	pg_data_t *pgdat = NODE_DATA(nid);
@@ -1745,7 +1751,7 @@  void try_offline_node(int nid)
 		return;
 	}
 
-	if (stop_machine(check_and_unmap_cpu_on_node, pgdat, NULL))
+	if (check_and_unmap_cpu_on_node(pgdat))
 		return;
 
 	/*
@@ -1782,6 +1788,13 @@  void try_offline_node(int nid)
 }
 EXPORT_SYMBOL(try_offline_node);
 
+/**
+ * remove_memory
+ *
+ * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
+ * and online/offline operations before this call, as required by
+ * try_offline_node().
+ */
 void __ref remove_memory(int nid, u64 start, u64 size)
 {
 	int ret;