arm64: Export save_stack_trace_tsk()

The kernel watchdog is a great debugging tool for finding tasks that
consume a disproportionate amount of CPU time in contiguous chunks. One
can imagine building a similar watchdog for arbitrary driver threads
using save_stack_trace_tsk() and print_stack_trace(). However, this is
not viable for dynamically loaded driver modules on ARM platforms
because save_stack_trace_tsk() is not exported for those architectures.
Export save_stack_trace_tsk() for the ARM64 architecture to align with
x86 and support various debugging use cases such as arbitrary driver
thread watchdog timers.
Signed-off-by: NDustin Brown <dustinb@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/kernel/stacktrace.c

@@ -210,6 +210,7 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 
 	put_task_stack(tsk);
 }
+EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
 
 void save_stack_trace(struct stack_trace *trace)
 {