On Wed 05-04-17 09:19:27, Michal Hocko wrote:
> On Wed 05-04-17 14:33:50, NeilBrown wrote:
[...]
> > diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> > index 0ecb6461ed81..44b3506fd086 100644
> > --- a/drivers/block/loop.c
> > +++ b/drivers/block/loop.c
> > @@ -852,6 +852,7 @@ static int loop_prepare_queue(struct loop_device *lo)
> > if (IS_ERR(lo->worker_task))
> > return -ENOMEM;
> > set_user_nice(lo->worker_task, MIN_NICE);
> > + lo->worker_task->flags |= PF_LESS_THROTTLE;
> > return 0;
>
> As mentioned elsewhere, PF flags should be updated only on the current
> task otherwise there is potential rmw race. Is this safe? The code runs
> concurrently with the worker thread.
I believe you need something like this instead
---
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index f347285c67ec..07b2a909e4fb 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -844,10 +844,16 @@ static void loop_unprepare_queue(struct loop_device *lo)
kthread_stop(lo->worker_task);
}
+int loop_kthread_worker_fn(void *worker_ptr)
+{
+ current->flags |= PF_LESS_THROTTLE;
+ return kthread_worker_fn(worker_ptr);
+}
+
static int loop_prepare_queue(struct loop_device *lo)
{
kthread_init_worker(&lo->worker);
- lo->worker_task = kthread_run(kthread_worker_fn,
+ lo->worker_task = kthread_run(loop_kthread_worker_fn,
&lo->worker, "loop%d", lo->lo_number);
if (IS_ERR(lo->worker_task))
return -ENOMEM;
--
Michal Hocko
SUSE Labs
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