Re: [PATCH 0/7] Containers (V8): Generic Process Containers

[Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>]

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Hi Paul,

In [patch 3/7] Containers (V8): Add generic multi-subsystem API to
containers, you have forcefully enabled interrupt in
container_init_subsys() with spin_unlock_irq() which breaks on PPC64.


> +static void container_init_subsys(struct container_subsys *ss) {
> +	int retval;
> +	struct list_head *l;
> +	printk(KERN_ERR "Initializing container subsys %s\n",
> ss->name);
> +
> +	/* Create the top container state for this subsystem */
> +	ss->root = &rootnode;
> +	retval = ss->create(ss, dummytop);
> +	BUG_ON(retval);
> +	init_container_css(ss, dummytop);
> +
> +	/* Update all container groups to contain a subsys
> +	 * pointer to this state - since the subsystem is
> +	 * newly registered, all tasks and hence all container
> +	 * groups are in the subsystem's top container. */
> +	spin_lock_irq(&container_group_lock);
> +	l = &init_container_group.list;
> +	do {
> +		struct container_group *cg =
> +			list_entry(l, struct container_group, list);
> +		cg->subsys[ss->subsys_id] =
> dummytop->subsys[ss->subsys_id];
> +		l = l->next;
> +	} while (l != &init_container_group.list);
> +	spin_unlock_irq(&container_group_lock);

Interrupt gets enabled here and on PPC64, the kernel takes a pending
decrementer and crashes because it is too early to handle them.

Use of irqsave and restore routines would fix the problem.
I have included the fix along with minor Kconfig correction.

Also your 3/7 patch did not showup on LKML.

--Vaidy

> +
> +	need_forkexit_callback |= ss->fork || ss->exit;

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Index: linux-2.6.20/kernel/container.c
===================================================================
--- linux-2.6.20.orig/kernel/container.c
+++ linux-2.6.20/kernel/container.c
@@ -1638,6 +1638,7 @@ int container_is_descendant(const struct
 
 static void container_init_subsys(struct container_subsys *ss) {
 	int retval;
+	unsigned long flags;
 	struct list_head *l;
 	printk(KERN_ERR "Initializing container subsys %s\n", ss->name);
 
@@ -1651,7 +1652,7 @@ static void container_init_subsys(struct
 	 * pointer to this state - since the subsystem is
 	 * newly registered, all tasks and hence all container
 	 * groups are in the subsystem's top container. */
-	spin_lock_irq(&container_group_lock);
+	spin_lock_irqsave(&container_group_lock, flags);
 	l = &init_container_group.list;
 	do {
 		struct container_group *cg =
@@ -1659,7 +1660,7 @@ static void container_init_subsys(struct
 		cg->subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];
 		l = l->next;
 	} while (l != &init_container_group.list);
-	spin_unlock_irq(&container_group_lock);
+	spin_unlock_irqrestore(&container_group_lock, flags);
 
 	need_forkexit_callback |= ss->fork || ss->exit;
 
Index: linux-2.6.20/init/Kconfig
===================================================================
--- linux-2.6.20.orig/init/Kconfig
+++ linux-2.6.20/init/Kconfig
@@ -239,8 +239,13 @@ config IKCONFIG_PROC
 	  through /proc/config.gz.
 
 config CONTAINERS
-	bool
-	
+	bool "Container support"
+	help
+	  This option will let you create and manage process containers,
+	  which can be used to aggregate multiple processes, e.g. for
+	  the purposes of resource tracking.
+
+	  Say N if unsure
 
 config CPUSETS
 	bool "Cpuset support"