[RFC PATCH 06/32] function_graph: Remove logic around ftrace_graph_entry and return

Masami Hiramatsu (Google)
2023-11-05T16:07:56Z

From: Steven Rostedt (VMware) <rostedt@goodmis.org>

The function pointers ftrace_graph_entry and ftrace_graph_return are no
longer called via the function_graph tracer. Instead, an array structure is
now used that will allow for multiple users of the function_graph
infrastructure. The variables are still used by the architecture code for
non dynamic ftrace configs, where a test is made against them to see if they
point to the default stub function or not. This is how the static function
tracing knows to call into the function graph tracer infrastructure or not.

Two new stub functions are made. entry_run() and return_run(). The
ftrace_graph_entry and ftrace_graph_return are set to them repectively when
the function graph tracer is enabled, and this will trigger the architecture
specific function graph code to be executed.

This also requires checking the global_ops hash for all calls into the
function_graph tracer.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
kernel/trace/fgraph.c | 72 +++++++++++-----------------------------
kernel/trace/ftrace.c | 2 -
kernel/trace/ftrace_internal.h | 2 -
3 files changed, 20 insertions(+), 56 deletions(-)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 58750a395313..78335be91007 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -128,6 +128,18 @@ static inline int get_fgraph_array(struct task_struct *t, int offset)
FGRAPH_ARRAY_MASK;
}

+/* ftrace_graph_entry set to this to tell some archs to run function graph */
+static int entry_run(struct ftrace_graph_ent *trace)
+{
+ return 0;
+}
+
+/* ftrace_graph_return set to this to tell some archs to run function graph */
+static void return_run(struct ftrace_graph_ret *trace)
+{
+ return;
+}
+
/*
* @offset: The index into @t->ret_stack to find the ret_stack entry
* @index: Where to place the index into @t->ret_stack of that entry
@@ -323,6 +335,10 @@ int function_graph_enter(unsigned long ret, unsigned long func,
ftrace_find_rec_direct(ret - MCOUNT_INSN_SIZE))
return -EBUSY;
#endif
+
+ if (!ftrace_ops_test(&global_ops, func, NULL))
+ return -EBUSY;
+
trace.func = func;
trace.depth = ++current->curr_ret_depth;

@@ -664,7 +680,6 @@ extern void ftrace_stub_graph(struct ftrace_graph_ret *);
/* The callbacks that hook a function */
trace_func_graph_ret_t ftrace_graph_return = ftrace_stub_graph;
trace_func_graph_ent_t ftrace_graph_entry = ftrace_graph_entry_stub;
-static trace_func_graph_ent_t __ftrace_graph_entry = ftrace_graph_entry_stub;

/* Try to assign a return stack array on FTRACE_RETSTACK_ALLOC_SIZE tasks. */
static int alloc_retstack_tasklist(unsigned long **ret_stack_list)
@@ -747,46 +762,6 @@ ftrace_graph_probe_sched_switch(void *ignore, bool preempt,
}
}

-static int ftrace_graph_entry_test(struct ftrace_graph_ent *trace)
-{
- if (!ftrace_ops_test(&global_ops, trace->func, NULL))
- return 0;
- return __ftrace_graph_entry(trace);
-}
-
-/*
- * The function graph tracer should only trace the functions defined
- * by set_ftrace_filter and set_ftrace_notrace. If another function
- * tracer ops is registered, the graph tracer requires testing the
- * function against the global ops, and not just trace any function
- * that any ftrace_ops registered.
- */
-void update_function_graph_func(void)
-{
- struct ftrace_ops *op;
- bool do_test = false;
-
- /*
- * The graph and global ops share the same set of functions
- * to test. If any other ops is on the list, then
- * the graph tracing needs to test if its the function
- * it should call.
- */
- do_for_each_ftrace_op(op, ftrace_ops_list) {
- if (op != &global_ops && op != &graph_ops &&
- op != &ftrace_list_end) {
- do_test = true;
- /* in double loop, break out with goto */
- goto out;
- }
- } while_for_each_ftrace_op(op);
- out:
- if (do_test)
- ftrace_graph_entry = ftrace_graph_entry_test;
- else
- ftrace_graph_entry = __ftrace_graph_entry;
-}
-
static DEFINE_PER_CPU(unsigned long *, idle_ret_stack);

static void
@@ -928,18 +903,12 @@ int register_ftrace_graph(struct fgraph_ops *gops)
ftrace_graph_active--;
goto out;
}
-
- ftrace_graph_return = gops->retfunc;
-
/*
- * Update the indirect function to the entryfunc, and the
- * function that gets called to the entry_test first. Then
- * call the update fgraph entry function to determine if
- * the entryfunc should be called directly or not.
+ * Some archs just test to see if these are not
+ * the default function
*/
- __ftrace_graph_entry = gops->entryfunc;
- ftrace_graph_entry = ftrace_graph_entry_test;
- update_function_graph_func();
+ ftrace_graph_return = return_run;
+ ftrace_graph_entry = entry_run;

ret = ftrace_startup(&graph_ops, FTRACE_START_FUNC_RET);
}
@@ -975,7 +944,6 @@ void unregister_ftrace_graph(struct fgraph_ops *gops)
if (!ftrace_graph_active) {
ftrace_graph_return = ftrace_stub_graph;
ftrace_graph_entry = ftrace_graph_entry_stub;
- __ftrace_graph_entry = ftrace_graph_entry_stub;
ftrace_shutdown(&graph_ops, FTRACE_STOP_FUNC_RET);
unregister_pm_notifier(&ftrace_suspend_notifier);
unregister_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 8de8bec5f366..fd64021ec52f 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -235,8 +235,6 @@ static void update_ftrace_function(void)
func = ftrace_ops_list_func;
}

- update_function_graph_func();
-
/* If there's no change, then do nothing more here */
if (ftrace_trace_function == func)
return;
diff --git a/kernel/trace/ftrace_internal.h b/kernel/trace/ftrace_internal.h
index 5012c04f92c0..19eddcb91584 100644
--- a/kernel/trace/ftrace_internal.h
+++ b/kernel/trace/ftrace_internal.h
@@ -42,10 +42,8 @@ ftrace_ops_test(struct ftrace_ops *ops, unsigned long ip, void *regs)

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
extern int ftrace_graph_active;
-void update_function_graph_func(void);
#else /* !CONFIG_FUNCTION_GRAPH_TRACER */
# define ftrace_graph_active 0
-static inline void update_function_graph_func(void) { }
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

#else /* !CONFIG_FUNCTION_TRACER */