On Mon 2016-01-11 18:17:18, Jacob Pan wrote:

On Fri, 8 Jan 2016 17:49:31 +0100
Petr Mladek [off-list ref] wrote:

quoted

Is the __preempt_schedule() a problem? It allows to switch the process
when needed. I thought that it was safe because try_to_freeze() might
have slept as well.

not a problem. i originally thought queue_kthread_work() may add
delay but it doesn't since there is no other work on this kthread.

Great.
 

quoted

quoted

- vulnerable to future changes of queuing work  

The question is if it is safe to sleep, freeze, or even migrate
the system between the works. It looks like because of the
try_to_freeze() and schedule_interrupt() calls in the original code.

BTW: I wonder if the original code correctly handle freezing after
the schedule_timeout(). It does not call try_to_freeze()
there and the forced idle states might block freezing.
I think that the small overhead of kthread works is worth
solving such bugs. It makes it easier to maintain these
sleeping states.

it is in a while loop, so try_to_freeze() gets called. Am I missing
something?

But it might take some time until try_to_freeze() is called.
If I get it correctly. try_to_freeze_tasks() wakes freezable
tasks to get them into the fridge. If clamp_thread() is waken
from that schedule_timeout_interruptible(), it still might inject
the idle state before calling try_to_freeze(). It means that freezer
needs to wait "quite" some time until the kthread ends up in the
fridge.

Hmm, even my conversion does not solve this entirely. We might
need to call freezing(current) in the

   while (time_before(jiffies, target_jiffies)) {

cycle. And break injecting the idle state when freezing is requested.

Or do I miss something, please?

Best Regards,
Petr







Best Regards,
Petr

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