ftrace: Hide one more entry in stack trace when ftrace_pid is enabled

On setting set_ftrace_pid, a extra entry generated by ftrace_pid_func()
is shown on stack trace(CONFIG_UNWINDER_FRAME_POINTER=y).

        [004] .....    68.459382: <stack trace>
 => 0xffffffffa00090af
 => ksys_read
 => __x64_sys_read
 => x64_sys_call
 => do_syscall_64
 => entry_SYSCALL_64_after_hwframe

To resolve this issue, increment skip count
in function_stack_trace_call() if pids are set.

Link: https://lore.kernel.org/linux-trace-kernel/20240528032604.6813-3-tatsuya.s2862@gmail.com

Signed-off-by: Tatsuya S <tatsuya.s2862@gmail.com>
[ Rebased to current tree ]
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: 66542e

kernel/trace/trace_functions.c

@@ -231,6 +231,7 @@ function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
 	long disabled;
 	int cpu;
 	unsigned int trace_ctx;
+	int skip = STACK_SKIP;
 
 	if (unlikely(!tr->function_enabled))
 		return;
@@ -247,7 +248,11 @@ function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
 	if (likely(disabled == 1)) {
 		trace_ctx = tracing_gen_ctx_flags(flags);
 		trace_function(tr, ip, parent_ip, trace_ctx);
-		__trace_stack(tr, trace_ctx, STACK_SKIP);
+#ifdef CONFIG_UNWINDER_FRAME_POINTER
+		if (ftrace_pids_enabled(op))
+			skip++;
+#endif
+		__trace_stack(tr, trace_ctx, skip);
 	}
 
 	atomic_dec(&data->disabled);