sched/group: prevent mm_free() of static g_kthread_group

When building for small systems with CONFIG_DEFAULT_SMALL=y, this
implies CONFIG_DISABLE_PTHREAD and thus HAVE_GROUP_MEMBERS is
undefined. When the AppBringUp task finishes, it will in this case
try to free g_kthread_group which is obviously not possible.

Add a guard with a new flag "GROUP_FLAG_STATIC" which indicates
the memory allocation type. Before freeing, check for this flag.

Signed-off-by: Maarten Zanders <maarten@zanders.be>

Author: mzanders

include/nuttx/sched.h

@@ -117,7 +117,8 @@
 #define GROUP_FLAG_PRIVILEGED      (1 << 1)                      /* Bit 1: Group is privileged */
 #define GROUP_FLAG_DELETED         (1 << 2)                      /* Bit 2: Group has been deleted but not yet freed */
 #define GROUP_FLAG_EXITING         (1 << 3)                      /* Bit 3: Group exit is in progress */
-                                                                 /* Bits 3-7: Available */
+#define GROUP_FLAG_STATIC          (1 << 4)                      /* Bit 4: Group is statically allocated */
+                                                                 /* Bits 5-7: Available */
 
 /* Values for struct child_status_s ch_flags */
 

sched/group/group_create.c

@@ -131,6 +131,7 @@ int group_allocate(FAR struct tcb_s *tcb, uint8_t ttype)
     {
       group = &g_kthread_group;
       tcb->group = group;
+      group->tg_flags |= GROUP_FLAG_STATIC;
       if (group->tg_info)
         {
           return OK;

sched/group/group_leave.c

@@ -238,7 +238,8 @@ void group_drop(FAR struct task_group_s *group)
 
   /* Finally, if no one needs the group and it has been deleted, remove it */
 
-  if (group->tg_flags & GROUP_FLAG_DELETED)
+  if ((group->tg_flags & GROUP_FLAG_DELETED) &&
+      !(group->tg_flags & GROUP_FLAG_STATIC))
     {
       /* Release the group container itself */