arm64: stacktrace: WARN_ON(state->common.pc == orig_pc) in kunwind_recover_return_address()

[Oleg Nesterov]

I don't know the details but people report that
kunwind_recover_return_address() hits this warning.

I know absolutely nothing about arm64 or kernel/trace/fgraph.c, but at
first glance this code looks broken:

	kunwind_recover_return_address:

		...

		orig_pc = ftrace_graph_ret_addr(state->task, NULL,
						state->common.pc,
						(void *)state->common.fp);
		if (WARN_ON_ONCE(state->common.pc == orig_pc))

	ftrace_graph_ret_addr:

		...

		if (!idx)
			return ret;


given that kunwind_recover_return_address() passes idx == NULL to
ftrace_graph_ret_addr(), it should always return ret == state->common.pc ?


Perhaps this connects to 29c1c24a27 ("function_graph: Fix up ftrace_graph_ret_addr()")
and I have no idea if something like the patch below makes any sense.

Oleg.

--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -106,7 +106,8 @@ kunwind_recover_return_address(struct kunwind_state *state)
 	if (state->task->ret_stack &&
 	    (state->common.pc == (unsigned long)return_to_handler)) {
 		unsigned long orig_pc;
-		orig_pc = ftrace_graph_ret_addr(state->task, NULL,
+		orig_pc = ftrace_graph_ret_addr(state->task,
+						&state->task->curr_ret_stack,
 						state->common.pc,
 						(void *)state->common.fp);
 		if (WARN_ON_ONCE(state->common.pc == orig_pc))