sched/sched/sched_releasetcb.c: Handle custom stack allocations.

sched_releasetcb() will normally free the stack allocated for a task.  However, a task with a custom, user-managed stack may be created using nxtask_init() followed by nxtask_activer.  If such a custom stack is used then it must not be free in this many or a crash will most likely result.

This chagne addes a flag call TCB_FLAG_CUSTOM_STACK that may be passed in the the pre-allocted TCB to nxtask_init().  This flag is not used internally anywhere in the OS except that if set, it will prevent sched_releasetcb() from freeing that custom stack.

include/nuttx/sched.h

@@ -103,9 +103,10 @@
 #  define TCB_FLAG_SCHED_SPORADIC  (2 << TCB_FLAG_POLICY_SHIFT)  /* Sporadic scheding policy */
 #  define TCB_FLAG_SCHED_OTHER     (3 << TCB_FLAG_POLICY_SHIFT)  /* Other scheding policy */
 #define TCB_FLAG_CPU_LOCKED        (1 << 7)                      /* Bit 7: Locked to this CPU */
-#define TCB_FLAG_SIGNAL_ACTION     (1 << 8)                      /* Bit 8: In a signal handler */
-#define TCB_FLAG_SYSCALL           (1 << 9)                      /* Bit 9: In a system call */
-#define TCB_FLAG_EXIT_PROCESSING   (1 << 10)                     /* Bit 10: Exitting */
+#define TCB_FLAG_CUSTOM_STACK      (1 << 8)                      /* Bit 8: Thread uses a custom stack */
+#define TCB_FLAG_SIGNAL_ACTION     (1 << 9)                      /* Bit 9: In a signal handler */
+#define TCB_FLAG_SYSCALL           (1 << 10)                     /* Bit 10: In a system call */
+#define TCB_FLAG_EXIT_PROCESSING   (1 << 11)                     /* Bit 11: Exitting */
                                                                  /* Bits 11-15: Available */
 
 /* Values for struct task_group tg_flags */
@@ -920,6 +921,14 @@ FAR struct socketlist *nxsched_get_sockets(void);
  *     2. Allocate the stack.  The pre-allocated stack is passed in argv.
  *     3. Activate the task. This must be done by calling nxtask_activate().
  *
+ *   Certain fields of the pre-allocated TCB may be set to change the
+ *   nature of the created task.  For example:
+ *
+ *     - Task type may be set in the TCB flags to create  kernel thread
+ *     - If a custom stack is used, i.e., one allocated, managed, and freed
+ *       by the caller, then TCB_FLAG_CUSTOM_STACK should be set in the
+ *       TCB flags.
+ *
  * Input Parameters:
  *   tcb        - Address of the new task's TCB
  *   name       - Name of the new task (not used)
@@ -954,6 +963,8 @@ int nxtask_init(FAR struct tcb_s *tcb, const char *name, int priority,
  *   was when a subsequent call to task_activate fails.
  *
  *   Caution:  Freeing of the TCB itself might be an unexpected side-effect.
+ *   The stack will also be freed UNLESS TCB_FLAG_CUSTOM_STACK was set in
+ *   in the tcb->flags field when nxtask_init() was called.
  *
  * Input Parameters:
  *   tcb - Address of the TCB initialized by task_init()

sched/sched/sched_releasetcb.c

@@ -127,9 +127,12 @@ int nxsched_release_tcb(FAR struct tcb_s *tcb, uint8_t ttype)
           nxsched_releasepid(tcb->pid);
         }
 
-      /* Delete the thread's stack if one has been allocated */
+      /* Delete the thread's stack if one has been allocated and it is
+       * not some custom stack managed by the caller.
+       */
 
-      if (tcb->stack_alloc_ptr)
+      if (tcb->stack_alloc_ptr &&
+          (tcb->flags & TCB_FLAG_CUSTOM_STACK) == 0)
         {
 #ifdef CONFIG_BUILD_KERNEL
           /* If the exiting thread is not a kernel thread, then it has an

sched/task/task_init.c

@@ -54,6 +54,14 @@
  *     2. Allocate the stack.  The pre-allocated stack is passed in argv.
  *     3. Activate the task. This must be done by calling nxtask_activate().
  *
+ *   Certain fields of the pre-allocated TCB may be set to change the
+ *   nature of the created task.  For example:
+ *
+ *     - Task type may be set in the TCB flags to create  kernel thread
+ *     - If a custom stack is used, i.e., one allocated, managed, and freed
+ *       by the caller, then TCB_FLAG_CUSTOM_STACK should be set in the
+ *       TCB flags.
+ *
  * Input Parameters:
  *   tcb        - Address of the new task's TCB
  *   name       - Name of the new task (not used)
@@ -148,6 +156,8 @@ errout:
  *   was when a subsequent call to task_activate fails.
  *
  *   Caution:  Freeing of the TCB itself might be an unexpected side-effect.
+ *   The stack will also be freed UNLESS TCB_FLAG_CUSTOM_STACK was set in
+ *   in the tcb->flags field when nxtask_init() was called.
  *
  * Input Parameters:
  *   tcb - Address of the TCB initialized by task_init()