Was last Barrier Patch OK?

Tue Mar 7 13:57:33 UTC 2006

Joel,

how often will I look at the patch and find bugs again, sigh!

In the macro _Thread_Disable_dispatch(), the memory barrier seems to be 
misplaced.

I have corrected it (hopefully) and nothing else in the attached patch.

So the temperature in Alabama is almost similar to munich, it seems. we 
got half a meter of snow this weekend, this is the absolute record at 
least for a century. And it just starts snowing again =8>

wkr,
Thomas.

Joel Sherrill wrote:
> Thomas Doerfler (nt) wrote:
> 
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> Till,
>>
>> ups, you got it, I actually missed that one when I checked the patch.
>>
>> Joel, can you fix it (AFTER! the camping trip with your boys)?
>>
>> wkr,
>> Thomas.
>>
>>
>>
>> Till Straumann schrieb:
>>  
>>
>>> Sorry, NO, it's still *not* OK.
>>>
>>> - the '.inl' version of _Thread_Unnest_dispatch()
>>>  has the barrier after the decrement operation instead
>>>  of before.
>>>
>>> Looks like you could use some vacation...
>>>
>>> ;-)
>>>
>>> -- T.
>>>   
> 
> 
> Yeah and time to recover from it afterwards. :)  We were near Auburn 
> Alabama and it got down
> below freezing Friday night.  The days were warm and sunny while the 
> nights were cold.  Combine
> that with the 4 hour drive there and I didn't get much sleep the first 
> night.  I will barely have time to
> catch up on my sleep before doing another trip to Montgomery this 
> weekend.  One of my sons is on
> the school Science Olympiad team which won the regional competition and 
> is going to state!
> 
> Anyway I think I have this all fixed in the attached patch.
>  critical section enter
>  barrier
>    protected operation
>  barrier
>  critical section exit
> 
> One other thought.  Can gcc move the critical section enter earlier and 
> exit later to include more
> in the critical section?
> --joel
> 
> 
> ------------------------------------------------------------------------
> 
> Index: cpukit/score/include/rtems/system.h
> ===================================================================
> RCS file: /usr1/CVS/rtems/cpukit/score/include/rtems/system.h,v
> retrieving revision 1.32.2.5
> diff -u -r1.32.2.5 system.h
> --- cpukit/score/include/rtems/system.h	14 Jan 2005 05:23:21 -0000	1.32.2.5
> +++ cpukit/score/include/rtems/system.h	7 Mar 2006 12:14:04 -0000
> @@ -102,6 +102,17 @@
>  #endif
>  
>  /*
> + *  The following macro is a compiler specific way to ensure that memory
> + *  writes are not reordered around certian points.  This specifically can
> + *  impact interrupt disable and thread dispatching critical sections.
> + */
> +#ifdef __GNUC__
> +  #define RTEMS_COMPILER_MEMORY_BARRIER() asm volatile("" ::: "memory")
> +#else
> +  #define RTEMS_COMPILER_MEMORY_BARRIER()
> +#endif
> +
> +/*
>   *  The following are used by the POSIX implementation to catch bad paths.
>   */
>  
> Index: cpukit/score/include/rtems/score/isr.h
> ===================================================================
> RCS file: /usr1/CVS/rtems/cpukit/score/include/rtems/score/isr.h,v
> retrieving revision 1.17.2.1
> diff -u -r1.17.2.1 isr.h
> --- cpukit/score/include/rtems/score/isr.h	4 Sep 2003 18:55:05 -0000	1.17.2.1
> +++ cpukit/score/include/rtems/score/isr.h	7 Mar 2006 12:14:04 -0000
> @@ -111,7 +111,10 @@
>   */
>  
>  #define _ISR_Disable( _level ) \
> -        _CPU_ISR_Disable( _level )
> +  do { \
> +    _CPU_ISR_Disable( _level ); \
> +    RTEMS_COMPILER_MEMORY_BARRIER(); \
> +  } while (0)
>  
>  /*
>   *  _ISR_Enable
> @@ -124,7 +127,10 @@
>   */
>  
>  #define _ISR_Enable( _level ) \
> -        _CPU_ISR_Enable( _level )
> +  do { \
> +    RTEMS_COMPILER_MEMORY_BARRIER(); \
> +    _CPU_ISR_Enable( _level ); \
> +  } while (0)
>  
>  /*
>   *  _ISR_Flash
> @@ -144,7 +150,11 @@
>   */
>  
>  #define _ISR_Flash( _level ) \
> -        _CPU_ISR_Flash( _level )
> +  do { \
> +    RTEMS_COMPILER_MEMORY_BARRIER(); \
> +    _CPU_ISR_Flash( _level ); \
> +    RTEMS_COMPILER_MEMORY_BARRIER(); \
> +  } while (0)
>  
>  /*
>   *  _ISR_Install_vector
> Index: cpukit/score/inline/rtems/score/thread.inl
> ===================================================================
> RCS file: /usr1/CVS/rtems/cpukit/score/inline/rtems/score/thread.inl,v
> retrieving revision 1.17.2.2
> diff -u -r1.17.2.2 thread.inl
> --- cpukit/score/inline/rtems/score/thread.inl	15 Sep 2003 02:12:47 -0000	1.17.2.2
> +++ cpukit/score/inline/rtems/score/thread.inl	7 Mar 2006 12:14:04 -0000
> @@ -184,6 +184,7 @@
>  RTEMS_INLINE_ROUTINE void _Thread_Disable_dispatch( void )
>  {
>    _Thread_Dispatch_disable_level += 1;
> +  RTEMS_COMPILER_MEMORY_BARRIER();
>  }
>  
>  /*PAGE
> @@ -201,6 +202,7 @@
>  #if ( CPU_INLINE_ENABLE_DISPATCH == TRUE )
>  RTEMS_INLINE_ROUTINE void _Thread_Enable_dispatch()
>  {
> +  RTEMS_COMPILER_MEMORY_BARRIER();
>    if ( (--_Thread_Dispatch_disable_level) == 0 )
>      _Thread_Dispatch();
>  }
> @@ -223,6 +225,7 @@
>  
>  RTEMS_INLINE_ROUTINE void _Thread_Unnest_dispatch( void )
>  {
> +  RTEMS_COMPILER_MEMORY_BARRIER();
>    _Thread_Dispatch_disable_level -= 1;
>  }
>  
> Index: cpukit/score/macros/rtems/score/thread.inl
> ===================================================================
> RCS file: /usr1/CVS/rtems/cpukit/score/macros/rtems/score/thread.inl,v
> retrieving revision 1.12.2.1
> diff -u -r1.12.2.1 thread.inl
> --- cpukit/score/macros/rtems/score/thread.inl	4 Sep 2003 18:55:06 -0000	1.12.2.1
> +++ cpukit/score/macros/rtems/score/thread.inl	7 Mar 2006 12:14:04 -0000
> @@ -126,7 +126,10 @@
>   */
>  
>  #define _Thread_Disable_dispatch() \
> -  _Thread_Dispatch_disable_level += 1
> +  do { \
> +    RTEMS_COMPILER_MEMORY_BARRIER(); \
> +    _Thread_Dispatch_disable_level += 1; \
> +  } while (0)
>  
>  /*PAGE
>   *
> @@ -136,9 +139,11 @@
>  
>  #if ( CPU_INLINE_ENABLE_DISPATCH == TRUE )
>  #define _Thread_Enable_dispatch()  \
> -      { if ( (--_Thread_Dispatch_disable_level) == 0 ) \
> -             _Thread_Dispatch();  \
> -      }
> +  do { \
> +    RTEMS_COMPILER_MEMORY_BARRIER(); \
> +    if ( (--_Thread_Dispatch_disable_level) == 0 ) \
> +       _Thread_Dispatch(); \
> +  } while (0)
>  #endif
>  
>  #if ( CPU_INLINE_ENABLE_DISPATCH == FALSE )
> @@ -152,7 +157,10 @@
>   */
>  
>  #define _Thread_Unnest_dispatch()  \
> -  _Thread_Dispatch_disable_level -= 1
> +  do { \
> +    RTEMS_COMPILER_MEMORY_BARRIER(); \
> +    _Thread_Dispatch_disable_level -= 1; \
> +  } while (0)
>  
>  /*PAGE
>   *

-- 
--------------------------------------------
IMD Ingenieurbuero fuer Microcomputertechnik
Thomas Doerfler           Herbststrasse 8
D-82178 Puchheim          Germany
email:    Thomas.Doerfler at imd-systems.de
PGP public key available at:
      http://www.imd-systems.de/pgpkey_en.html
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