On 2019-01-09 16:59:26 [+0100], Daniel Bristot de Oliveira wrote:
> diff --git a/kernel/padata.c b/kernel/padata.c
> index d568cc56405f..bfcbdeb20ba5 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -295,7 +295,7 @@ static void padata_reorder_timer(struct timer_list *t)
> unsigned int weight;
> int target_cpu, cpu;
>
> - cpu = get_cpu();
> + cpu = get_cpu_light();
This can become a
cpu = smp_processor_id()
> /* We don't lock pd here to not interfere with parallel processing
> * padata_reorder() calls on other CPUs. We just need any CPU out of
> @@ -321,7 +321,7 @@ static void padata_reorder_timer(struct timer_list *t)
> padata_reorder(pd);
> }
>
> - put_cpu();
> + put_cpu_light();
and this can go because this is invoked in a timer callback.
> }
>
> static void padata_serial_worker(struct work_struct *serial_work)
> @@ -369,7 +369,7 @@ void padata_do_serial(struct padata_priv *padata)
>
> pd = padata->pd;
>
> - cpu = get_cpu();
> + cpu = get_cpu_light();
this is tricky but I would also say that this can become
smp_processor_id() like in the upper hunk
> /* We need to run on the same CPU padata_do_parallel(.., padata, ..)
> * was called on -- or, at least, enqueue the padata object into the
> @@ -387,7 +387,7 @@ void padata_do_serial(struct padata_priv *padata)
> list_add_tail(&padata->list, &pqueue->reorder.list);
> spin_unlock(&pqueue->reorder.lock);
>
> - put_cpu();
> + put_cpu_light();
and than this can go, too. It looks like this invoked from a worker with
BH disabled. If it does, it is all good. If not then it might be
problematic because later we have
queue_work_on(cpu, pd->pinst->wq, &pqueue->reorder_work);
and nothing guarantees that the work is carried out by the CPU specified
if CPU-hotplug is involved.
> /* If we're running on the wrong CPU, call padata_reorder() via a
> * kernel worker.
Sebastian
