Messages in this thread | | | Subject | Re: Bug in scheduler when using rt_mutex | From | Peter Zijlstra <> | Date | Mon, 17 Jan 2011 16:00:01 +0100 |
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On Mon, 2011-01-17 at 16:42 +0200, Onkalo Samu wrote: > Hi > > I believe that there are some problems in the scheduling when > the following happens: > - Normal priority process locks rt_mutex and sleeps while keeping it > locked.
There's your fail, don't do that!
> - RT priority process blocks on the rt_mutex while normal priority > process is sleeping > > This sequence can occur with I2C access when both normal priority > thread and irq-thread access the same I2C bus. I2C core > contains rt_mutex and I2C drivers can sleep with wait_for_completion.
Why does I2C core use rt_mutex, that's utterly broken.
> Based on my debugging following sequence occurs (single CPU > system): > > 1) There is some user process running at the background (like > cat /dev/zero..) > 2) User process reads sysfs entry which causes I2C acccess > 3) User process locks rt_mutex in the I2C-core > 4) User process sleeps while it keeps rt_mutex locked > (wait_for_completion in I2C transfer function)
That's where things go wrong, there's absolutely nothing you can do to fix the system once you block while holding a mutex.
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