From 5e15bafd26374981b4ad06e545d0c9ae65217ea0 Mon Sep 17 00:00:00 2001 From: Darian Leung Date: Tue, 19 Jul 2022 12:13:54 +0800 Subject: [PATCH 1/2] freertos: Fix event group task list race condition FreeRTOS synchronization primitives (e.g., queues, eventgroups) use various event lists (i.e., task lists) to track what tasks are blocked on a current primitive. Usually these event lists are accessed via one of the event lists functions (such as vTask[PlaceOn|RemoveFrom]UnorderedEventList()), which in turn ensure that the global task list spinlock (xTaskQueueMutex) is taken when accessing these lists. However, some functions in event_groups.c manually traverse their event lists. Thus if a tick interrupt occurs on another core during traversal and that tick interrupt unblocks a task on the event list being traversed, the event list will be corrupted. This commit modifies the following event_groups.c functions so that they take the global task list lock before traversing their event list. - xEventGroupSetBits() - vEventGroupDelete() --- components/freertos/event_groups.c | 13 +++++++++++++ components/freertos/include/freertos/task.h | 17 +++++++++++++++++ components/freertos/tasks.c | 18 +++++++++++++++--- 3 files changed, 45 insertions(+), 3 deletions(-) diff --git a/components/freertos/event_groups.c b/components/freertos/event_groups.c index 3a06e23740..ab5f06ebb9 100644 --- a/components/freertos/event_groups.c +++ b/components/freertos/event_groups.c @@ -565,6 +565,10 @@ BaseType_t xMatchFound = pdFALSE; vTaskSuspendAll(); taskENTER_CRITICAL(&pxEventBits->eventGroupMux); + /* The critical section above only takes the event groups spinlock. However, we are about to traverse a task list. + Thus we need call the function below to take the task list spinlock located in tasks.c. Not doing so will risk + the task list's being changed while be are traversing it. */ + vTaskTakeEventListLock(); { traceEVENT_GROUP_SET_BITS( xEventGroup, uxBitsToSet ); @@ -636,6 +640,8 @@ BaseType_t xMatchFound = pdFALSE; bit was set in the control word. */ pxEventBits->uxEventBits &= ~uxBitsToClear; } + /* Release the previously held task list spinlock, then release the event group spinlock. */ + vTaskReleaseEventListLock(); taskEXIT_CRITICAL(&pxEventBits->eventGroupMux); ( void ) xTaskResumeAll(); @@ -650,6 +656,10 @@ void vEventGroupDelete( EventGroupHandle_t xEventGroup ) vTaskSuspendAll(); taskENTER_CRITICAL( &pxEventBits->eventGroupMux ); + /* The critical section above only takes the event groups spinlock. However, we are about to traverse a task list. + Thus we need call the function below to take the task list spinlock located in tasks.c. Not doing so will risk + the task list's being changed while be are traversing it. */ + vTaskTakeEventListLock(); { traceEVENT_GROUP_DELETE( xEventGroup ); @@ -661,6 +671,9 @@ void vEventGroupDelete( EventGroupHandle_t xEventGroup ) ( void ) xTaskRemoveFromUnorderedEventList( pxTasksWaitingForBits->xListEnd.pxNext, eventUNBLOCKED_DUE_TO_BIT_SET ); } + /* Release the previously held task list spinlock. */ + vTaskReleaseEventListLock(); + #if( ( configSUPPORT_DYNAMIC_ALLOCATION == 1 ) && ( configSUPPORT_STATIC_ALLOCATION == 0 ) ) { /* The event group can only have been allocated dynamically - free diff --git a/components/freertos/include/freertos/task.h b/components/freertos/include/freertos/task.h index cfea1f0a77..20fc935365 100644 --- a/components/freertos/include/freertos/task.h +++ b/components/freertos/include/freertos/task.h @@ -2152,6 +2152,23 @@ void vTaskPlaceOnUnorderedEventList( List_t * pxEventList, const TickType_t xIte */ void vTaskPlaceOnEventListRestricted( List_t * const pxEventList, const TickType_t xTicksToWait ) PRIVILEGED_FUNCTION; +/* + * THIS FUNCTION MUST NOT BE USED FROM APPLICATION CODE. IT IS AN + * INTERFACE WHICH IS FOR THE EXCLUSIVE USE OF THE SCHEDULER. + * + * This function is a wrapper to take the "xTaskQueueMutex" spinlock of tasks.c. + * This lock is taken whenver any of the task lists or event lists are + * accessed/modified, such as when adding/removing tasks to/from the delayed + * task list or various event lists. + * + * This functions is meant to be called by xEventGroupSetBits() and + * vEventGroupDelete() as both those functions will access event lists (instead + * of delegating the entire responsibility to one of vTask...EventList() + * functions). + */ +void vTaskTakeEventListLock( void ); +void vTaskReleaseEventListLock( void ); + /* * THIS FUNCTION MUST NOT BE USED FROM APPLICATION CODE. IT IS AN * INTERFACE WHICH IS FOR THE EXCLUSIVE USE OF THE SCHEDULER. diff --git a/components/freertos/tasks.c b/components/freertos/tasks.c index 1d07e6c8e1..64fca604b7 100644 --- a/components/freertos/tasks.c +++ b/components/freertos/tasks.c @@ -2865,11 +2865,11 @@ void vTaskSwitchContext( void ) --uxDynamicTopReady; } -#else +#else //For Unicore targets we can keep the current FreeRTOS O(1) - //Scheduler. I hope to optimize better the scheduler for + //Scheduler. I hope to optimize better the scheduler for //Multicore settings -- This will involve to create a per - //affinity ready task list which will impact hugely on + //affinity ready task list which will impact hugely on //tasks module taskSELECT_HIGHEST_PRIORITY_TASK(); #endif @@ -3168,6 +3168,18 @@ UBaseType_t i, uxTargetCPU; } /*-----------------------------------------------------------*/ +void vTaskTakeEventListLock( void ) +{ + /* We call the tasks.c critical section macro to take xTaskQueueMutex */ + taskENTER_CRITICAL(&xTaskQueueMutex); +} + +void vTaskReleaseEventListLock( void ) +{ + /* We call the tasks.c critical section macro to release xTaskQueueMutex */ + taskEXIT_CRITICAL(&xTaskQueueMutex); +} + BaseType_t xTaskRemoveFromUnorderedEventList( ListItem_t * pxEventListItem, const TickType_t xItemValue ) { TCB_t *pxUnblockedTCB; From c7c07c5fb2776cf1ddf07b666ea4ac9bf4b11a4e Mon Sep 17 00:00:00 2001 From: Darian Leung Date: Tue, 19 Jul 2022 12:19:42 +0800 Subject: [PATCH 2/2] freertos: Fix flakey event group unit test The "FreeRTOS Event Groups" main task will only wait a single tick for the created tasks to set their response bits. This short delay may not be sufficent if the tick frequency is high. This commit updates the test so that - the main task waits indefinitely for all the response bits to be set. - created tasks are cleaned up by the main task --- .../freertos/test/test_freertos_eventgroups.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/components/freertos/test/test_freertos_eventgroups.c b/components/freertos/test/test_freertos_eventgroups.c index 9b3800a5aa..3ccb8e390f 100644 --- a/components/freertos/test/test_freertos_eventgroups.c +++ b/components/freertos/test/test_freertos_eventgroups.c @@ -7,6 +7,7 @@ #include "freertos/event_groups.h" #include "driver/timer.h" #include "unity.h" +#include "test_utils.h" #ifdef CONFIG_IDF_TARGET_ESP32S2 #define int_clr_timers int_clr @@ -40,7 +41,8 @@ static void task_event_group_call_response(void *param) printf("Task %d done\n", task_num); xSemaphoreGive(done_sem); - vTaskDelete(NULL); + // Wait to be deleted + vTaskSuspend(NULL); } TEST_CASE("FreeRTOS Event Groups", "[freertos]") @@ -48,6 +50,8 @@ TEST_CASE("FreeRTOS Event Groups", "[freertos]") eg = xEventGroupCreate(); done_sem = xSemaphoreCreateCounting(NUM_TASKS, 0); + TaskHandle_t task_handles[NUM_TASKS]; + /* Note: task_event_group_call_response all have higher priority than this task, so on this core they will always preempt this task. @@ -55,7 +59,7 @@ TEST_CASE("FreeRTOS Event Groups", "[freertos]") or they get out of sync. */ for (int c = 0; c < NUM_TASKS; c++) { - xTaskCreatePinnedToCore(task_event_group_call_response, "tsk_call_resp", 4096, (void *)c, configMAX_PRIORITIES - 1, NULL, c % portNUM_PROCESSORS); + xTaskCreatePinnedToCore(task_event_group_call_response, "tsk_call_resp", 4096, (void *)c, configMAX_PRIORITIES - 1, &task_handles[c], c % portNUM_PROCESSORS); } /* Tasks all start instantly, but this task will resume running at the same time as the higher priority tasks on the @@ -66,15 +70,19 @@ TEST_CASE("FreeRTOS Event Groups", "[freertos]") /* signal all tasks with "CALL" bit... */ xEventGroupSetBits(eg, BIT_CALL); - /* Only wait for 1 tick, the wakeup should be immediate... */ - TEST_ASSERT_EQUAL_HEX16(ALL_RESPONSE_BITS, xEventGroupWaitBits(eg, ALL_RESPONSE_BITS, true, true, 1)); + /* Wait until all tasks have set their respective response bits */ + TEST_ASSERT_EQUAL_HEX16(ALL_RESPONSE_BITS, xEventGroupWaitBits(eg, ALL_RESPONSE_BITS, true, true, portMAX_DELAY)); } - /* Ensure all tasks cleaned up correctly */ + /* Ensure all tasks have suspend themselves */ for (int c = 0; c < NUM_TASKS; c++) { TEST_ASSERT( xSemaphoreTake(done_sem, 100/portTICK_PERIOD_MS) ); } + for (int c = 0; c < NUM_TASKS; c++) { + test_utils_task_delete(task_handles[c]); + } + vSemaphoreDelete(done_sem); vEventGroupDelete(eg); }