Re: [PATCH 1/1] hotplug cpu: move tasks in empty cpusets to parent

["Paul Menage" <menage@google.com>]

On 5/22/07, Cliff Wickman <cpw@sgi.com> wrote:
> - * Call with both manage_mutex and callback_mutex held.
> + * Call with both manage_sem and callback_sem held so
> + * that this function can modify cpus_allowed and mems_allowed.
>   *
> - * Recursive, on depth of cpuset subtree.
> + * This walk processes the tree from top to bottom, completing one layer
> + * before dropping down to the next.  It always processes a node before
> + * any of its children.
>   */
> +static void remove_tasks_from_empty_cpusets(const struct cpuset *root, int *count)
> +{
> +       struct cpuset *cp;      /* scans cpusets being updated */
> +       struct cpuset *child;   /* scans child cpusets of cp */
> +       struct kfifo *queue;    /* fifo queue of cpusets to be updated */
> +
> +       queue = kfifo_alloc(number_of_cpusets * sizeof(cp), GFP_KERNEL, NULL);
> +       if (queue == ERR_PTR(-ENOMEM))
> +               return;

You can't call memory allocation functions while holding
callback_mutex - otherwise you can theoretically deadlock if
_alloc_pages() calls cpuset_zone_allowed_*()

Paul

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