[patch 1/2] mm, hotplug: fix error handling in mem_online_node()

[patch 1/2] mm, hotplug: fix error handling in mem_online_node()

[David Rientjes]

The error handling in mem_online_node() is incorrect: hotadd_new_pgdat() 
returns NULL if the new pgdat could not have been allocated and a pointer 
to it otherwise.

mem_online_node() should fail if hotadd_new_pgdat() fails, not the 
inverse.  This fixes an issue when memoryless nodes are not onlined and 
their sysfs interface is not registered when their first cpu is brought 
up.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/memory_hotplug.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -521,7 +521,7 @@ int mem_online_node(int nid)
 
 	lock_memory_hotplug();
 	pgdat = hotadd_new_pgdat(nid, 0);
-	if (pgdat) {
+	if (!pgdat) {
 		ret = -ENOMEM;
 		goto out;
 	}

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[patch 2/2] mm, hotplug: protect zonelist building with zonelists_mutex

[David Rientjes]

959ecc48fc75 ("mm/memory_hotplug.c: fix building of node hotplug 
zonelist") does not protect the build_all_zonelists() call with 
zonelists_mutex as needed.  This can lead to races in constructing 
zonelist ordering if a concurrent build is underway.  Protecting this with 
lock_memory_hotplug() is insufficient since zonelists can be rebuild 
though sysfs as well.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/memory_hotplug.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -498,7 +498,9 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
 	 * The node we allocated has no zone fallback lists. For avoiding
 	 * to access not-initialized zonelist, build here.
 	 */
+	mutex_lock(&zonelists_mutex);
 	build_all_zonelists(NULL);
+	mutex_unlock(&zonelists_mutex);
 
 	return pgdat;
 }

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Re: [patch 1/2] mm, hotplug: fix error handling in mem_online_node()

[KOSAKI Motohiro]

(2011/06/23 10:13), David Rientjes wrote:
> The error handling in mem_online_node() is incorrect: hotadd_new_pgdat() 
> returns NULL if the new pgdat could not have been allocated and a pointer 
> to it otherwise.
> 
> mem_online_node() should fail if hotadd_new_pgdat() fails, not the 
> inverse.  This fixes an issue when memoryless nodes are not onlined and 
> their sysfs interface is not registered when their first cpu is brought 
> up.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

Nice catch.

The fault was introduced by commit cf23422b9d76(cpu/mem hotplug: enable CPUs
online before local memory online) iow v2.6.35.

 Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>


> ---
>  mm/memory_hotplug.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -521,7 +521,7 @@ int mem_online_node(int nid)
>  
>  	lock_memory_hotplug();
>  	pgdat = hotadd_new_pgdat(nid, 0);
> -	if (pgdat) {
> +	if (!pgdat) {
>  		ret = -ENOMEM;
>  		goto out;
>  	}
> 
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> 
> 


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Re: [patch 2/2] mm, hotplug: protect zonelist building with zonelists_mutex

[KOSAKI Motohiro]

(2011/06/23 10:13), David Rientjes wrote:
> 959ecc48fc75 ("mm/memory_hotplug.c: fix building of node hotplug 
> zonelist") does not protect the build_all_zonelists() call with 
> zonelists_mutex as needed.  This can lead to races in constructing 
> zonelist ordering if a concurrent build is underway.  Protecting this with 
> lock_memory_hotplug() is insufficient since zonelists can be rebuild 
> though sysfs as well.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

Indeed.

 Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

> ---
>  mm/memory_hotplug.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -498,7 +498,9 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
>  	 * The node we allocated has no zone fallback lists. For avoiding
>  	 * to access not-initialized zonelist, build here.
>  	 */
> +	mutex_lock(&zonelists_mutex);
>  	build_all_zonelists(NULL);
> +	mutex_unlock(&zonelists_mutex);
>  
>  	return pgdat;
>  }
> 
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> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
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> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
> 
> 


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