LoongArch: Check unwind_error() in arch_stack_walk()

We can see the following messages with CONFIG_PROVE_LOCKING=y on
LoongArch:

  BUG: MAX_STACK_TRACE_ENTRIES too low!
  turning off the locking correctness validator.

This is because stack_trace_save() returns a big value after call
arch_stack_walk(), here is the call trace:

  save_trace()
    stack_trace_save()
      arch_stack_walk()
        stack_trace_consume_entry()

arch_stack_walk() should return immediately if unwind_next_frame()
failed, no need to do the useless loops to increase the value of c->len
in stack_trace_consume_entry(), then we can fix the above problem.

Cc: stable@vger.kernel.org
Reported-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/all/8a44ad71-68d2-4926-892f-72bfc7a67e2a@roeck-us.net/Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/kernel/stacktrace.c

@@ -30,7 +30,7 @@ void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
 
 	regs->regs[1] = 0;
 	for (unwind_start(&state, task, regs);
-	      !unwind_done(&state); unwind_next_frame(&state)) {
+	     !unwind_done(&state) && !unwind_error(&state); unwind_next_frame(&state)) {
 		addr = unwind_get_return_address(&state);
 		if (!addr || !consume_entry(cookie, addr))
 			break;

arch/loongarch/kernel/unwind.c

@@ -28,5 +28,6 @@ bool default_next_frame(struct unwind_state *state)
 
 	} while (!get_stack_info(state->sp, state->task, info));
 
+	state->error = true;
 	return false;
 }

arch/loongarch/kernel/unwind_prologue.c

@@ -211,7 +211,7 @@ static bool next_frame(struct unwind_state *state)
 			pc = regs->csr_era;
 
 			if (user_mode(regs) || !__kernel_text_address(pc))
-				return false;
+				goto out;
 
 			state->first = true;
 			state->pc = pc;
@@ -226,6 +226,8 @@ static bool next_frame(struct unwind_state *state)
 
 	} while (!get_stack_info(state->sp, state->task, info));
 
+out:
+	state->error = true;
 	return false;
 }