lkml.org 
[lkml]   [2011]   [Jan]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: Bug in scheduler when using rt_mutex
From
Date
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.



\
 
 \ /
  Last update: 2011-01-17 16:01    [W:0.108 / U:1.944 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site