When CONFIG_DISABLE_PTHREAD=y, HAVE_GROUP_MEMBERS is undefined and
group_leave() unconditionally calls group_release() for every exiting
thread. This destroys the shared g_kthread_group resources (mutex,
fdlist, task_info) while other kernel threads are still using them,
causing use-after-free crashes.
Fix by checking TCB_FLAG_TTYPE_KERNEL in group_leave() before calling
group_release(), so the entire release path is skipped for kernel
threads. This is safe because g_kthread_group is statically allocated
and its lifetime is the entire system.
Signed-off-by: wangyongrong <wangyongrong@xiaomi.com>