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Fix xTaskNotifyWait & ulTaskNotifyTake determinism. #833

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merged 6 commits into from
Oct 17, 2023
Merged

Fix xTaskNotifyWait & ulTaskNotifyTake determinism. #833

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e654143
Fix task notification determinism.
Oct 13, 2023
1043460
Fix formatting.
Oct 13, 2023
acbb51b
Remove duplicate statement
kar-rahul-aws Oct 13, 2023
2c7e573
Merge branch 'main' into pr_625_final
aggarg Oct 16, 2023
3df0cba
Code review suggestions
aggarg Oct 16, 2023
3d8e07e
Merge branch 'main' into pr_625_final
aggarg Oct 17, 2023
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147 changes: 116 additions & 31 deletions tasks.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5198,7 +5198,7 @@ void vTaskPlaceOnEventList( List_t * const pxEventList,

configASSERT( pxEventList );

/* THIS FUNCTION MUST BE CALLED WITH EITHER INTERRUPTS DISABLED OR THE
/* THIS FUNCTION MUST BE CALLED WITH THE
* SCHEDULER SUSPENDED AND THE QUEUE BEING ACCESSED LOCKED. */

/* Place the event list item of the TCB in the appropriate event list.
Expand Down Expand Up @@ -7480,28 +7480,68 @@ TickType_t uxTaskResetEventItemValue( void )
TickType_t xTicksToWait )
{
uint32_t ulReturn;
BaseType_t xAlreadyYielded;

traceENTER_ulTaskGenericNotifyTake( uxIndexToWaitOn, xClearCountOnExit, xTicksToWait );

configASSERT( uxIndexToWaitOn < configTASK_NOTIFICATION_ARRAY_ENTRIES );

taskENTER_CRITICAL();

/* Only block if the notification count is not already non-zero. */
if( pxCurrentTCB->ulNotifiedValue[ uxIndexToWaitOn ] == 0UL )
{
/* Only block if the notification count is not already non-zero. */
if( pxCurrentTCB->ulNotifiedValue[ uxIndexToWaitOn ] == 0UL )
/* Mark this task as waiting for a notification. */
pxCurrentTCB->ucNotifyState[ uxIndexToWaitOn ] = taskWAITING_NOTIFICATION;

if( xTicksToWait > ( TickType_t ) 0 )
{
/* Mark this task as waiting for a notification. */
pxCurrentTCB->ucNotifyState[ uxIndexToWaitOn ] = taskWAITING_NOTIFICATION;
traceTASK_NOTIFY_TAKE_BLOCK( uxIndexToWaitOn );

if( xTicksToWait > ( TickType_t ) 0 )
/* We MUST suspend the scheduler before exiting the critical
* section (i.e. before enabling interrupts).
*
* If we do not do so, a notification sent from an ISR, which
* happens after exiting the critical section and before
* suspending the scheduler, will get lost. The sequence of
* events will be:
* 1. Exit critical section.
* 2. Interrupt - ISR calls xTaskNotifyFromISR which adds the
* task to the Ready list.
* 3. Suspend scheduler.
* 4. prvAddCurrentTaskToDelayedList moves the task to the
* delayed or suspended list.
* 5. Resume scheduler does not touch the task (because it is
* not on the pendingReady list), effectively losing the
* notification from the ISR.
*
* The same does not happen when we suspend the scheduler before
* exiting the critical section. The sequence of events in this
* case will be:
* 1. Suspend scheduler.
* 2. Exit critical section.
* 3. Interrupt - ISR calls xTaskNotifyFromISR which adds the
* task to the pendingReady list as the scheduler is
* suspended.
* 4. prvAddCurrentTaskToDelayedList adds the task to delayed or
* suspended list. Note that this operation does not nullify
* the add to pendingReady list done in the above step because
* a different list item, namely xEventListItem, is used for
* adding the task to the pendingReady list. In other words,
* the task still remains on the pendingReady list.
* 5. Resume scheduler moves the task from pendingReady list to
* the Ready list.
*/
vTaskSuspendAll();
{
taskEXIT_CRITICAL();

prvAddCurrentTaskToDelayedList( xTicksToWait, pdTRUE );
traceTASK_NOTIFY_TAKE_BLOCK( uxIndexToWaitOn );
}
xAlreadyYielded = xTaskResumeAll();

/* All ports are written to allow a yield in a critical
* section (some will yield immediately, others wait until the
* critical section exits) - but it is not something that
* application code should ever do. */
if( xAlreadyYielded == pdFALSE )
{
taskYIELD_WITHIN_API();
}
else
Expand All @@ -7511,10 +7551,13 @@ TickType_t uxTaskResetEventItemValue( void )
}
else
{
mtCOVERAGE_TEST_MARKER();
taskEXIT_CRITICAL();
}
}
taskEXIT_CRITICAL();
else
{
taskEXIT_CRITICAL();
}

taskENTER_CRITICAL();
{
Expand Down Expand Up @@ -7557,34 +7600,73 @@ TickType_t uxTaskResetEventItemValue( void )
uint32_t * pulNotificationValue,
TickType_t xTicksToWait )
{
BaseType_t xReturn;
BaseType_t xReturn, xAlreadyYielded;

traceENTER_xTaskGenericNotifyWait( uxIndexToWaitOn, ulBitsToClearOnEntry, ulBitsToClearOnExit, pulNotificationValue, xTicksToWait );

configASSERT( uxIndexToWaitOn < configTASK_NOTIFICATION_ARRAY_ENTRIES );

taskENTER_CRITICAL();

/* Only block if a notification is not already pending. */
if( pxCurrentTCB->ucNotifyState[ uxIndexToWaitOn ] != taskNOTIFICATION_RECEIVED )
{
/* Only block if a notification is not already pending. */
if( pxCurrentTCB->ucNotifyState[ uxIndexToWaitOn ] != taskNOTIFICATION_RECEIVED )
{
/* Clear bits in the task's notification value as bits may get
* set by the notifying task or interrupt. This can be used to
* clear the value to zero. */
pxCurrentTCB->ulNotifiedValue[ uxIndexToWaitOn ] &= ~ulBitsToClearOnEntry;
/* Clear bits in the task's notification value as bits may get
* set by the notifying task or interrupt. This can be used to
* clear the value to zero. */
pxCurrentTCB->ulNotifiedValue[ uxIndexToWaitOn ] &= ~ulBitsToClearOnEntry;

/* Mark this task as waiting for a notification. */
pxCurrentTCB->ucNotifyState[ uxIndexToWaitOn ] = taskWAITING_NOTIFICATION;
/* Mark this task as waiting for a notification. */
pxCurrentTCB->ucNotifyState[ uxIndexToWaitOn ] = taskWAITING_NOTIFICATION;

if( xTicksToWait > ( TickType_t ) 0 )
if( xTicksToWait > ( TickType_t ) 0 )
{
traceTASK_NOTIFY_WAIT_BLOCK( uxIndexToWaitOn );

/* We MUST suspend the scheduler before exiting the critical
* section (i.e. before enabling interrupts).
*
* If we do not do so, a notification sent from an ISR, which
* happens after exiting the critical section and before
* suspending the scheduler, will get lost. The sequence of
* events will be:
* 1. Exit critical section.
* 2. Interrupt - ISR calls xTaskNotifyFromISR which adds the
* task to the Ready list.
* 3. Suspend scheduler.
* 4. prvAddCurrentTaskToDelayedList moves the task to the
* delayed or suspended list.
* 5. Resume scheduler does not touch the task (because it is
* not on the pendingReady list), effectively losing the
* notification from the ISR.
*
* The same does not happen when we suspend the scheduler before
* exiting the critical section. The sequence of events in this
* case will be:
* 1. Suspend scheduler.
* 2. Exit critical section.
* 3. Interrupt - ISR calls xTaskNotifyFromISR which adds the
* task to the pendingReady list as the scheduler is
* suspended.
* 4. prvAddCurrentTaskToDelayedList adds the task to delayed or
* suspended list. Note that this operation does not nullify
* the add to pendingReady list done in the above step because
* a different list item, namely xEventListItem, is used for
* adding the task to the pendingReady list. In other words,
* the task still remains on the pendingReady list.
* 5. Resume scheduler moves the task from pendingReady list to
* the Ready list.
*/
vTaskSuspendAll();
{
taskEXIT_CRITICAL();

prvAddCurrentTaskToDelayedList( xTicksToWait, pdTRUE );
traceTASK_NOTIFY_WAIT_BLOCK( uxIndexToWaitOn );
}
xAlreadyYielded = xTaskResumeAll();

/* All ports are written to allow a yield in a critical
* section (some will yield immediately, others wait until the
* critical section exits) - but it is not something that
* application code should ever do. */
if( xAlreadyYielded == pdFALSE )
{
taskYIELD_WITHIN_API();
}
else
Expand All @@ -7594,10 +7676,13 @@ TickType_t uxTaskResetEventItemValue( void )
}
else
{
mtCOVERAGE_TEST_MARKER();
taskEXIT_CRITICAL();
}
}
taskEXIT_CRITICAL();
else
{
taskEXIT_CRITICAL();
}

taskENTER_CRITICAL();
{
Expand Down
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