Before the MPU initialization, the up_update_task(this_cpu()) function is called at a time when hardware cache coherency is not yet enabled.
In certain critical scenarios, Core 1 reads a zero value for tcb from the global variable g_assignedtask and stores this zero value into the tpidr
register. This results in subsequent interrupt handlers reading a zero tcb, causing an exception.
Signed-off-by: hujun5 <hujun5@xiaomi.com>