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SubjectRe: [PATCH 3/9] [I/OAT] Setup the networking subsystem as a DMA client
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From: Chris Leech <christopher.leech@intel.com>
Date: Tue, 23 May 2006 17:20:15 -0700

> +static void net_dma_rebalance(void)
> +{
> + unsigned int cpu, i, n;
> + struct dma_chan *chan;
> +
> + lock_cpu_hotplug();

You can't call lock_cpu_hotplug(), because that sleeps and takes
semaphores and we currently hold a spinlock taken here:

> +static void netdev_dma_event(struct dma_client *client, struct dma_chan *chan,
> + enum dma_event event)
> +{
> + spin_lock(&net_dma_event_lock);
> + switch (event) {
> + case DMA_RESOURCE_ADDED:
> + net_dma_count++;
> + net_dma_rebalance();
> + break;

You'll need to run this DMA rebalancing asynchronously in process
context via keventd or similar to deal with this locking bug.
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