linux-kernel - Re: [PATCH 3/7] containers (V7): Add generic multi-subsystem API to containers

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Date:	Thu, 8 Mar 2007 23:22:33 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	menage@...gle.com
Cc:	akpm@...l.org, pj@....com, sekharan@...ibm.com, dev@...ru,
	xemul@...ru, serue@...ibm.com, ebiederm@...ssion.com,
	ckrm-tech@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	rohitseth@...gle.com, mbligh@...gle.com, winget@...gle.com,
	containers@...ts.osdl.org, devel@...nvz.org
Subject: Re: [PATCH 3/7] containers (V7): Add generic multi-subsystem API to containers

On Mon, Feb 12, 2007 at 12:15:24AM -0800, menage@...gle.com wrote:
> +static struct container_group *find_container_group(
> +	struct container_group *oldcg, struct container *cont)
> +{
> +	struct container_group *res;
> +	struct container_subsys *ss;
> +	int h = cont->hierarchy;
> +	int i;
> +
> +	BUG_ON(oldcg->container[h] == cont);
> +	/* First see if we already have a container group that matches
> +	 * the desired set */
> +	spin_lock(&container_group_lock);

I think this should be spin_lock_irq().

I have been bitten by lockdep warning in the rcfs patchs. But I think
they should apply here as well.

Essentially, container_task_count() is called from cpuset.c after doing
write_lock_irq(tasklist_lock). This creates the dependency:

	tasklist_lock (irqs disabled)  -> container_group_lock

However in above function, find_container_group (and several other
functions) we take container_group_lock w/o blocking interrupts. An
interrupt handler now trying to take tasklist_lock will cause a
deadlock.

-- 
Regards,
vatsa
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