[PATCH] cpukit/score: avoid NULL and races in priority mutex

[Mathew Benson]

This piqued my interest due to an issue we ran into several months ago.
Just so I can better understand this, what is "PIP"?  Are you referring to
maybe Priority Inversion Protection?


On Thu, Jan 2, 2020 at 5:25 PM Gedare Bloom <gedare at rtems.org> wrote:

> The PIP modifications from #3359 introduced new data structures
> to track priority inheritance. Prioritized mutexes without PIP
> share some of the code paths, and may result in NULL pointer
> accesses. This patch checks for NULL, and also adds ISR critical
> sections to an uncovered corner case during thread restarts.
>
> Closes #3829.
> ---
>  cpukit/score/src/threadqextractpriority.c | 4 +++-
>  cpukit/score/src/threadreset.c            | 5 +++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/cpukit/score/src/threadqextractpriority.c
> b/cpukit/score/src/threadqextractpriority.c
> index 5c8188d661..9288d17980 100644
> --- a/cpukit/score/src/threadqextractpriority.c
> +++ b/cpukit/score/src/threadqextractpriority.c
> @@ -109,7 +109,9 @@ bool _Thread_queue_Extract_priority_helper(
>    }
>
>    mutex = _Thread_Dequeue_priority_node( &the_thread->Priority_node );
> -  _Thread_Evaluate_priority( mutex->holder );
> +  if ( mutex != NULL ) {
> +    _Thread_Evaluate_priority( mutex->holder );
> +  }
>
>    if ( !_Watchdog_Is_active( &the_thread->Timer ) ) {
>      _ISR_Enable( level );
> diff --git a/cpukit/score/src/threadreset.c
> b/cpukit/score/src/threadreset.c
> index 464a611391..dfc85c93aa 100644
> --- a/cpukit/score/src/threadreset.c
> +++ b/cpukit/score/src/threadreset.c
> @@ -48,6 +48,7 @@ void _Thread_Reset(
>  )
>  {
>    CORE_mutex_Control *mutex;
> +  ISR_Level              level;
>
>    the_thread->resource_count   = 0;
>    #if defined(RTEMS_ITRON_API)
> @@ -66,17 +67,21 @@ void _Thread_Reset(
>        (void) _Watchdog_Remove( &the_thread->Timer );
>    }
>
> +  _ISR_Disable( level );
>    if ( the_thread->Priority_node.waiting_to_hold != NULL ) {
>      mutex = _Thread_Dequeue_priority_node( &the_thread->Priority_node );
>      _Thread_Evaluate_priority( mutex->holder );
>    }
> +  _ISR_Enable( level );
>
>    while ( !_Chain_Is_empty(
> &the_thread->Priority_node.Inherited_priorities ) ) {
> +    _ISR_Disable( level );
>      _Thread_Dequeue_priority_node(
>        ((Thread_Priority_node*)_Chain_First(
>          &the_thread->Priority_node.Inherited_priorities
>        ))
>      );
> +    _ISR_Enable( level );
>    }
>
>    if ( the_thread->Priority_node.current_priority !=
> the_thread->Start.initial_priority ) {
> --
> 2.17.1
>
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>


-- 
*Mathew Benson*
CEO | Chief Engineer
Windhover Labs, LLC
832-640-4018


www.windhoverlabs.com
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