[PATCH] cgroups: fix lockdep subclasses overflow

[PATCH] cgroups: fix lockdep subclasses overflow

[Li Zefan]

I enabled all cgroup subsystems when compiling kernel, and then:
 # mount -t cgroup -o net_cls xxx /mnt
 # mkdir /mnt/0

This showed up immediately:
 BUG: MAX_LOCKDEP_SUBCLASSES too low!
 turning off the locking correctness validator.

It's caused by the cgroup hierarchy lock:
	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
		struct cgroup_subsys *ss = subsys[i];
		if (ss->root == root)
			mutex_lock_nested(&ss->hierarchy_mutex, i);
	}

Now we have 9 cgroup subsystems, and the above 'i' for net_cls is 9, but
MAX_LOCKDEP_SUBCLASSES is 8.

This patch uses different lockdep keys for different subsystems.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 include/linux/cgroup.h |    1 +
 kernel/cgroup.c        |    3 ++-
 2 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e4e8e11..499900d 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -378,6 +378,7 @@ struct cgroup_subsys {
 	 * - initiating hotplug events
 	 */
 	struct mutex hierarchy_mutex;
+	struct lock_class_key subsys_key;
 
 	/*
 	 * Link to parent, and list entry in parent's children.
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5a54ff4..e14db9c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2351,7 +2351,7 @@ static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
 	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 		struct cgroup_subsys *ss = subsys[i];
 		if (ss->root == root)
-			mutex_lock_nested(&ss->hierarchy_mutex, i);
+			mutex_lock(&ss->hierarchy_mutex);
 	}
 }
 
@@ -2637,6 +2637,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
 	BUG_ON(!list_empty(&init_task.tasks));
 
 	mutex_init(&ss->hierarchy_mutex);
+	lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
 	ss->active = 1;
 }
 
-- 
1.5.4.rc3

Re: [PATCH] cgroups: fix lockdep subclasses overflow

[Li Zefan]

Li Zefan wrote:
> I enabled all cgroup subsystems when compiling kernel, and then:
>  # mount -t cgroup -o net_cls xxx /mnt
>  # mkdir /mnt/0
> 
> This showed up immediately:
>  BUG: MAX_LOCKDEP_SUBCLASSES too low!
>  turning off the locking correctness validator.
> 
> It's caused by the cgroup hierarchy lock:
> 	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
> 		struct cgroup_subsys *ss = subsys[i];
> 		if (ss->root == root)
> 			mutex_lock_nested(&ss->hierarchy_mutex, i);
> 	}
> 
> Now we have 9 cgroup subsystems, and the above 'i' for net_cls is 9, but

sorry, a typo here: the above 'i' for net_cls is 8.

> MAX_LOCKDEP_SUBCLASSES is 8.
> 
> This patch uses different lockdep keys for different subsystems.
> 
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> ---

Re: [PATCH] cgroups: fix lockdep subclasses overflow

[Paul Menage]

On Wed, Feb 4, 2009 at 1:11 AM, Li Zefan <lizf@cn.fujitsu.com> wrote:
>
> This patch uses different lockdep keys for different subsystems.
>
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

Acked-by: Paul Menage <menage@google.com>

Looks good, thanks.

Paul

> ---
>  include/linux/cgroup.h |    1 +
>  kernel/cgroup.c        |    3 ++-
>  2 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index e4e8e11..499900d 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -378,6 +378,7 @@ struct cgroup_subsys {
>         * - initiating hotplug events
>         */
>        struct mutex hierarchy_mutex;
> +       struct lock_class_key subsys_key;
>
>        /*
>         * Link to parent, and list entry in parent's children.
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 5a54ff4..e14db9c 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -2351,7 +2351,7 @@ static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
>        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
>                struct cgroup_subsys *ss = subsys[i];
>                if (ss->root == root)
> -                       mutex_lock_nested(&ss->hierarchy_mutex, i);
> +                       mutex_lock(&ss->hierarchy_mutex);
>        }
>  }
>
> @@ -2637,6 +2637,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
>        BUG_ON(!list_empty(&init_task.tasks));
>
>        mutex_init(&ss->hierarchy_mutex);
> +       lockdep_set_class(&ss->hierarchy_mutex, &ss->subsys_key);
>        ss->active = 1;
>  }
>
> --
> 1.5.4.rc3
>
>
>
>