function_graph: Add pid tracing back to function graph tracer

Now that the function_graph has a main callback that handles the function
graph subops tracing, it no longer honors the pid filtering of ftrace. Add
back this logic in the function_graph code to update the gops callback for
the entry function to test if it should trace the current task or not.

Link: https://lore.kernel.org/linux-trace-kernel/20240603190822.991720703@goodmis.org

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: bpf <bpf@vger.kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alan Maguire <alan.maguire@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Guo Ren <guoren@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

include/linux/ftrace.h

@@ -1040,6 +1040,7 @@ typedef int (*trace_func_graph_ent_t)(struct ftrace_graph_ent *,
 				      struct fgraph_ops *); /* entry */
 
 extern int ftrace_graph_entry_stub(struct ftrace_graph_ent *trace, struct fgraph_ops *gops);
+bool ftrace_pids_enabled(struct ftrace_ops *ops);
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 
@@ -1048,6 +1049,7 @@ struct fgraph_ops {
 	trace_func_graph_ret_t		retfunc;
 	struct ftrace_ops		ops; /* for the hash lists */
 	void				*private;
+	trace_func_graph_ent_t		saved_func;
 	int				idx;
 };
 

kernel/trace/fgraph.c

@@ -854,6 +854,41 @@ void ftrace_graph_exit_task(struct task_struct *t)
 	kfree(ret_stack);
 }
 
+static int fgraph_pid_func(struct ftrace_graph_ent *trace,
+			   struct fgraph_ops *gops)
+{
+	struct trace_array *tr = gops->ops.private;
+	int pid;
+
+	if (tr) {
+		pid = this_cpu_read(tr->array_buffer.data->ftrace_ignore_pid);
+		if (pid == FTRACE_PID_IGNORE)
+			return 0;
+		if (pid != FTRACE_PID_TRACE &&
+		    pid != current->pid)
+			return 0;
+	}
+
+	return gops->saved_func(trace, gops);
+}
+
+void fgraph_update_pid_func(void)
+{
+	struct fgraph_ops *gops;
+	struct ftrace_ops *op;
+
+	if (!(graph_ops.flags & FTRACE_OPS_FL_INITIALIZED))
+		return;
+
+	list_for_each_entry(op, &graph_ops.subop_list, list) {
+		if (op->flags & FTRACE_OPS_FL_PID) {
+			gops = container_of(op, struct fgraph_ops, ops);
+			gops->entryfunc = ftrace_pids_enabled(op) ?
+				fgraph_pid_func : gops->saved_func;
+		}
+	}
+}
+
 /* Allocate a return stack for each task */
 static int start_graph_tracing(void)
 {
@@ -931,11 +966,15 @@ int register_ftrace_graph(struct fgraph_ops *gops)
 		command = FTRACE_START_FUNC_RET;
 	}
 
+	/* Always save the function, and reset at unregistering */
+	gops->saved_func = gops->entryfunc;
+
 	ret = ftrace_startup_subops(&graph_ops, &gops->ops, command);
 error:
 	if (ret) {
 		fgraph_array[i] = &fgraph_stub;
 		ftrace_graph_active--;
+		gops->saved_func = NULL;
 	}
 out:
 	mutex_unlock(&ftrace_lock);
@@ -979,5 +1018,6 @@ void unregister_ftrace_graph(struct fgraph_ops *gops)
 		unregister_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);
 	}
  out:
+	gops->saved_func = NULL;
 	mutex_unlock(&ftrace_lock);
 }

kernel/trace/ftrace.c

@@ -100,7 +100,7 @@ struct ftrace_ops *function_trace_op __read_mostly = &ftrace_list_end;
 /* What to set function_trace_op to */
 static struct ftrace_ops *set_function_trace_op;
 
-static bool ftrace_pids_enabled(struct ftrace_ops *ops)
+bool ftrace_pids_enabled(struct ftrace_ops *ops)
 {
 	struct trace_array *tr;
 
@@ -402,10 +402,11 @@ static void ftrace_update_pid_func(void)
 		if (op->flags & FTRACE_OPS_FL_PID) {
 			op->func = ftrace_pids_enabled(op) ?
 				ftrace_pid_func : op->saved_func;
-			ftrace_update_trampoline(op);
 		}
 	} while_for_each_ftrace_op(op);
 
+	fgraph_update_pid_func();
+
 	update_ftrace_function();
 }
 

kernel/trace/ftrace_internal.h

@@ -43,8 +43,10 @@ ftrace_ops_test(struct ftrace_ops *ops, unsigned long ip, void *regs)
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 extern int ftrace_graph_active;
+extern void fgraph_update_pid_func(void);
 #else /* !CONFIG_FUNCTION_GRAPH_TRACER */
 # define ftrace_graph_active 0
+static inline void fgraph_update_pid_func(void) {}
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 
 #else /* !CONFIG_FUNCTION_TRACER */