diff mbox series

[RFC,v2,12/31] function_graph: Have the instances use their own ftrace_ops for filtering

Message ID 169945360154.55307.2938894711228282149.stgit@devnote2 (mailing list archive)
State RFC
Headers show
Series tracing: fprobe: function_graph: Multi-function graph and fprobe on fgraph | expand

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Commit Message

Masami Hiramatsu (Google) Nov. 8, 2023, 2:26 p.m. UTC 
From: Steven Rostedt (VMware) <rostedt@goodmis.org>

Allow for instances to have their own ftrace_ops part of the fgraph_ops
that makes the funtion_graph tracer filter on the set_ftrace_filter file
of the instance and not the top instance.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 Changes in v2:
  - Use ftrace_graph_func and FTRACE_OPS_GRAPH_STUB instead of
    ftrace_stub and FTRACE_OPS_FL_STUB for new ftrace based fgraph.
---
 include/linux/ftrace.h               |    1 +
 kernel/trace/fgraph.c                |   60 +++++++++++++++++++++-------------
 kernel/trace/ftrace.c                |    6 ++-
 kernel/trace/trace.h                 |   16 +++++----
 kernel/trace/trace_functions.c       |    2 +
 kernel/trace/trace_functions_graph.c |    8 +++--
 6 files changed, 58 insertions(+), 35 deletions(-)

Comments

Masami Hiramatsu (Google) Nov. 10, 2023, 1:51 a.m. UTC | #1 
Hi,

I found strange behavior that if we set two or more probes on the same function,
its callback called twice or more. Also, the stacktrace failed.
And I found the root cause is here;

On Wed,  8 Nov 2023 23:26:42 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> @@ -910,9 +917,10 @@ int register_ftrace_graph(struct fgraph_ops *gops)
>  		 */
>  		ftrace_graph_return = return_run;
>  		ftrace_graph_entry = entry_run;
> -
> -		ret = ftrace_startup(&graph_ops, FTRACE_START_FUNC_RET);
> +		command = FTRACE_START_FUNC_RET;
>  	}
> +
> +	ret = ftrace_startup(&gops->ops, command);

So this patch registers ftrace_ops for each fgraph_ops to ftrace.
This means that the ftrace_graph_func() will be called twice or more
on the same function.
Thus should I call ftrace_startup() once when the first fgraph_ops
is registered? 
No, it's not enough. Actually each fgraph_ops can have different filters.
We need to define a shared filter and combine new filters to one and
use it. We also need to do it when a fgraph is unregistered.

Is there any function which makes a new filter from two (or more) filters?

Or, maybe we can make the common callback to find the previous ret entry on
the ret_stack and reuse it. (In this case we don't need loop on each
fgraph_array entry)

Thank you,
Steven Rostedt Nov. 10, 2023, 2:18 a.m. UTC | #2 
On Fri, 10 Nov 2023 10:51:54 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> So this patch registers ftrace_ops for each fgraph_ops to ftrace.
> This means that the ftrace_graph_func() will be called twice or more
> on the same function.
> Thus should I call ftrace_startup() once when the first fgraph_ops
> is registered? 
> No, it's not enough. Actually each fgraph_ops can have different filters.
> We need to define a shared filter and combine new filters to one and
> use it. We also need to do it when a fgraph is unregistered.
> 
> Is there any function which makes a new filter from two (or more) filters?

So I'm guessing that we need to have a fgraph_set_filter*() operations?

When one gets added, it needs to update the ftrace_ops to include the added
functions. Or we need to have a way to create a new hash from all the
registered fgraph_ops, and have that for the ftrace_ops. Then when it gets
called, if it has more than one registered function, it needs to iterate
over the list?

-- Steve


> 
> Or, maybe we can make the common callback to find the previous ret entry on
> the ret_stack and reuse it. (In this case we don't need loop on each
> fgraph_array entry)
Masami Hiramatsu (Google) Nov. 10, 2023, 3:09 a.m. UTC | #3 
On Thu, 9 Nov 2023 21:18:48 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 10 Nov 2023 10:51:54 +0900
> Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:
> 
> > So this patch registers ftrace_ops for each fgraph_ops to ftrace.
> > This means that the ftrace_graph_func() will be called twice or more
> > on the same function.
> > Thus should I call ftrace_startup() once when the first fgraph_ops
> > is registered? 
> > No, it's not enough. Actually each fgraph_ops can have different filters.
> > We need to define a shared filter and combine new filters to one and
> > use it. We also need to do it when a fgraph is unregistered.
> > 
> > Is there any function which makes a new filter from two (or more) filters?
> 
> So I'm guessing that we need to have a fgraph_set_filter*() operations?
> 
> When one gets added, it needs to update the ftrace_ops to include the added
> functions. Or we need to have a way to create a new hash from all the
> registered fgraph_ops, and have that for the ftrace_ops. Then when it gets
> called, if it has more than one registered function, it needs to iterate
> over the list?

Yes, that is one option, update a global common hash and introduce a new
common ftrace function to run function_graph_enter().

Or, I think keep the current one but iterate ftrace_ops to callback the
function_graph_enter() with ftrace_ops. Then we can get appropriate
fgraph_ops. Ftrace push return trace can skip pushing if ret == return_to_handler.
(maybe this is better to reuse ftrace)

Thank you,

> 
> -- Steve
> 
> 
> > 
> > Or, maybe we can make the common callback to find the previous ret entry on
> > the ret_stack and reuse it. (In this case we don't need loop on each
> > fgraph_array entry)
>
diff mbox series

Patch

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 84e06ad1b121..d30eb8a97a50 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -1069,6 +1069,7 @@  extern int ftrace_graph_entry_stub(struct ftrace_graph_ent *trace, struct fgraph
 struct fgraph_ops {
 	trace_func_graph_ent_t		entryfunc;
 	trace_func_graph_ret_t		retfunc;
+	struct ftrace_ops		ops; /* for the hash lists */
 	void				*private;
 };
 
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 16bbb9fa3e03..97cf320d20a8 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -17,14 +17,6 @@ 
 #include "ftrace_internal.h"
 #include "trace.h"
 
-#ifdef CONFIG_DYNAMIC_FTRACE
-#define ASSIGN_OPS_HASH(opsname, val) \
-	.func_hash		= val, \
-	.local_hash.regex_lock	= __MUTEX_INITIALIZER(opsname.local_hash.regex_lock),
-#else
-#define ASSIGN_OPS_HASH(opsname, val)
-#endif
-
 #define FGRAPH_RET_SIZE sizeof(struct ftrace_ret_stack)
 #define FGRAPH_RET_INDEX (FGRAPH_RET_SIZE / sizeof(long))
 
@@ -337,9 +329,6 @@  int function_graph_enter(unsigned long ret, unsigned long func,
 		return -EBUSY;
 #endif
 
-	if (!ftrace_ops_test(&global_ops, func, NULL))
-		return -EBUSY;
-
 	trace.func = func;
 	trace.depth = ++current->curr_ret_depth;
 
@@ -360,7 +349,8 @@  int function_graph_enter(unsigned long ret, unsigned long func,
 			atomic_inc(&current->trace_overrun);
 			break;
 		}
-		if (fgraph_array[i]->entryfunc(&trace, fgraph_array[i])) {
+		if (ftrace_ops_test(&gops->ops, func, NULL) &&
+		    gops->entryfunc(&trace, gops)) {
 			offset = current->curr_ret_stack;
 			/* Check the top level stored word */
 			type = get_fgraph_type(current, offset - 1);
@@ -655,17 +645,25 @@  unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
 }
 #endif /* HAVE_FUNCTION_GRAPH_RET_ADDR_PTR */
 
-static struct ftrace_ops graph_ops = {
-	.func			= ftrace_graph_func,
-	.flags			= FTRACE_OPS_FL_INITIALIZED |
-				   FTRACE_OPS_FL_PID |
-				   FTRACE_OPS_GRAPH_STUB,
+void fgraph_init_ops(struct ftrace_ops *dst_ops,
+		     struct ftrace_ops *src_ops)
+{
+	dst_ops->func = ftrace_graph_func;
+	dst_ops->flags = FTRACE_OPS_FL_PID | FTRACE_OPS_GRAPH_STUB;
+
 #ifdef FTRACE_GRAPH_TRAMP_ADDR
-	.trampoline		= FTRACE_GRAPH_TRAMP_ADDR,
+	dst_ops->trampoline = FTRACE_GRAPH_TRAMP_ADDR;
 	/* trampoline_size is only needed for dynamically allocated tramps */
 #endif
-	ASSIGN_OPS_HASH(graph_ops, &global_ops.local_hash)
-};
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+	if (src_ops) {
+		dst_ops->func_hash = &src_ops->local_hash;
+		mutex_init(&dst_ops->local_hash.regex_lock);
+		dst_ops->flags |= FTRACE_OPS_FL_INITIALIZED;
+	}
+#endif
+}
 
 void ftrace_graph_sleep_time_control(bool enable)
 {
@@ -870,11 +868,20 @@  static int start_graph_tracing(void)
 
 int register_ftrace_graph(struct fgraph_ops *gops)
 {
+	int command = 0;
 	int ret = 0;
 	int i;
 
 	mutex_lock(&ftrace_lock);
 
+	if (!gops->ops.func) {
+		gops->ops.flags |= FTRACE_OPS_GRAPH_STUB;
+		gops->ops.func = ftrace_graph_func;
+#ifdef FTRACE_GRAPH_TRAMP_ADDR
+		gops->ops.trampoline = FTRACE_GRAPH_TRAMP_ADDR;
+#endif
+	}
+
 	if (!fgraph_array[0]) {
 		/* The array must always have real data on it */
 		for (i = 0; i < FGRAPH_ARRAY_SIZE; i++)
@@ -910,9 +917,10 @@  int register_ftrace_graph(struct fgraph_ops *gops)
 		 */
 		ftrace_graph_return = return_run;
 		ftrace_graph_entry = entry_run;
-
-		ret = ftrace_startup(&graph_ops, FTRACE_START_FUNC_RET);
+		command = FTRACE_START_FUNC_RET;
 	}
+
+	ret = ftrace_startup(&gops->ops, command);
 out:
 	mutex_unlock(&ftrace_lock);
 	return ret;
@@ -920,6 +928,7 @@  int register_ftrace_graph(struct fgraph_ops *gops)
 
 void unregister_ftrace_graph(struct fgraph_ops *gops)
 {
+	int command = 0;
 	int i;
 
 	mutex_lock(&ftrace_lock);
@@ -942,10 +951,15 @@  void unregister_ftrace_graph(struct fgraph_ops *gops)
 	}
 
 	ftrace_graph_active--;
+
+	if (!ftrace_graph_active)
+		command = FTRACE_STOP_FUNC_RET;
+
+	ftrace_shutdown(&gops->ops, command);
+
 	if (!ftrace_graph_active) {
 		ftrace_graph_return = ftrace_stub_graph;
 		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 83fbfb7b48f8..c4cc2a9d0047 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3050,6 +3050,8 @@  int ftrace_startup(struct ftrace_ops *ops, int command)
 	if (unlikely(ftrace_disabled))
 		return -ENODEV;
 
+	ftrace_ops_init(ops);
+
 	ret = __register_ftrace_function(ops);
 	if (ret)
 		return ret;
@@ -7319,7 +7321,7 @@  __init void ftrace_init_global_array_ops(struct trace_array *tr)
 	tr->ops = &global_ops;
 	tr->ops->private = tr;
 	ftrace_init_trace_array(tr);
-	init_array_fgraph_ops(tr);
+	init_array_fgraph_ops(tr, tr->ops);
 }
 
 void ftrace_init_array_ops(struct trace_array *tr, ftrace_func_t func)
@@ -8051,7 +8053,7 @@  static int register_ftrace_function_nolock(struct ftrace_ops *ops)
  */
 int register_ftrace_function(struct ftrace_ops *ops)
 {
-	int ret;
+	int ret = -1;
 
 	lock_direct_mutex();
 	ret = prepare_direct_functions_for_ipmodify(ops);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index febb9c6d01c7..f77322e3b177 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -885,8 +885,8 @@  extern int __trace_graph_entry(struct trace_array *tr,
 extern void __trace_graph_return(struct trace_array *tr,
 				 struct ftrace_graph_ret *trace,
 				 unsigned int trace_ctx);
-extern void init_array_fgraph_ops(struct trace_array *tr);
-extern int allocate_fgraph_ops(struct trace_array *tr);
+extern void init_array_fgraph_ops(struct trace_array *tr, struct ftrace_ops *ops);
+extern int allocate_fgraph_ops(struct trace_array *tr, struct ftrace_ops *ops);
 extern void free_fgraph_ops(struct trace_array *tr);
 
 #ifdef CONFIG_DYNAMIC_FTRACE
@@ -969,6 +969,7 @@  static inline int ftrace_graph_notrace_addr(unsigned long addr)
 	preempt_enable_notrace();
 	return ret;
 }
+
 #else
 static inline int ftrace_graph_addr(struct ftrace_graph_ent *trace)
 {
@@ -994,18 +995,19 @@  static inline bool ftrace_graph_ignore_func(struct ftrace_graph_ent *trace)
 		(fgraph_max_depth && trace->depth >= fgraph_max_depth);
 }
 
+void fgraph_init_ops(struct ftrace_ops *dst_ops,
+		     struct ftrace_ops *src_ops);
+
 #else /* CONFIG_FUNCTION_GRAPH_TRACER */
 static inline enum print_line_t
 print_graph_function_flags(struct trace_iterator *iter, u32 flags)
 {
 	return TRACE_TYPE_UNHANDLED;
 }
-static inline void init_array_fgraph_ops(struct trace_array *tr) { }
-static inline int allocate_fgraph_ops(struct trace_array *tr)
-{
-	return 0;
-}
 static inline void free_fgraph_ops(struct trace_array *tr) { }
+/* ftrace_ops may not be defined */
+#define init_array_fgraph_ops(tr, ops) do { } while (0)
+#define allocate_fgraph_ops(tr, ops) ({ 0; })
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 
 extern struct list_head ftrace_pids;
diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 8e8da0d0ee52..13bf2415245d 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -91,7 +91,7 @@  int ftrace_create_function_files(struct trace_array *tr,
 	if (!tr->ops)
 		return -EINVAL;
 
-	ret = allocate_fgraph_ops(tr);
+	ret = allocate_fgraph_ops(tr, tr->ops);
 	if (ret) {
 		kfree(tr->ops);
 		return ret;
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 9ccc904a7703..7f30652f0e97 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -288,7 +288,7 @@  static struct fgraph_ops funcgraph_ops = {
 	.retfunc = &trace_graph_return,
 };
 
-int allocate_fgraph_ops(struct trace_array *tr)
+int allocate_fgraph_ops(struct trace_array *tr, struct ftrace_ops *ops)
 {
 	struct fgraph_ops *gops;
 
@@ -301,6 +301,9 @@  int allocate_fgraph_ops(struct trace_array *tr)
 
 	tr->gops = gops;
 	gops->private = tr;
+
+	fgraph_init_ops(&gops->ops, ops);
+
 	return 0;
 }
 
@@ -309,10 +312,11 @@  void free_fgraph_ops(struct trace_array *tr)
 	kfree(tr->gops);
 }
 
-__init void init_array_fgraph_ops(struct trace_array *tr)
+__init void init_array_fgraph_ops(struct trace_array *tr, struct ftrace_ops *ops)
 {
 	tr->gops = &funcgraph_ops;
 	funcgraph_ops.private = tr;
+	fgraph_init_ops(&tr->gops->ops, ops);
 }
 
 static int graph_trace_init(struct trace_array *tr)