Re: [PATCH] workqueue: Restore cpus_allowed mask for sleeping workqueue rescue threads

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2011-08-31 at 14:17 +0100, Ripduman Sohan wrote:
> Rescuer threads may be migrated (and are bound) to particular CPUs when
> active.  However, the allowed_cpus mask is not restored when they return
> to sleep rendering inconsistent the presented and actual set of CPUs the
> process may potentially run on.  This patch fixes this oversight by
> recording the allowed_cpus mask for rescuer threads when it enters the
> rescuer_thread() main loop and restoring it every time the thread sleeps.
> 
> Signed-off-by: Ripduman Sohan <ripduman.sohan@cl.cam.ac.uk>
> ---
>  kernel/workqueue.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 25fb1b0..0a4e785 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -2031,6 +2031,7 @@ static int rescuer_thread(void *__wq)
>  	struct list_head *scheduled = &rescuer->scheduled;
>  	bool is_unbound = wq->flags & WQ_UNBOUND;
>  	unsigned int cpu;
> +        cpumask_t allowed_cpus = current->cpus_allowed;

except you cannot just allocate a cpumask_t like that on the stack,
those things can be massive.

>  	set_user_nice(current, RESCUER_NICE_LEVEL);
>  repeat:
> @@ -2078,6 +2079,8 @@ repeat:
>  		spin_unlock_irq(&gcwq->lock);
>  	}
>  
> +        set_cpus_allowed_ptr(current, &allowed_cpus);
> +
>  	schedule();
>  	goto repeat;
>  }