On 08/16/2017 02:17 PM, Steven Rostedt wrote:

On Wed, 16 Aug 2017 14:14:36 -0400
Waiman Long [off-list ref] wrote:

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You also just turned the mutex into a spinlock. What happens if we ju=

st

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preempted the owner of bdev->bd_mutex and are an RT task with higher
priority? This will turn into a live lock.
=20

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+		schedule();
+	}
  =20

That is OK because I used schedule() instead of cpu_relax() for
inserting delay.

Please explain to me how that is OK? schedule is a nop if the current
task is the highest priority task running, and it preempted the owner
of the lock. Nothing will actually schedule.

-- Steve

I haven't been thinking about RT tasks. You are right that it can be a
problem in this case. I think I will have to revert back to use
mutex_lock() if a RT task is running. Though in this case, the lock
inversion problem will still be there. However, it is highly unlikely
that a RT task will need to read write the block trace sysfs files.

Thanks for the input.

Cheers,
Longman