linux-kernel - Re: [PATCH RFC tip/perf/core] ftrace/x86: Let dynamic trampolines call ops->func even for dynamic fops

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Message-ID: <20150402161242.06bbcfdf@gandalf.local.home>
Date:	Thu, 2 Apr 2015 16:12:42 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Miroslav Benes <mbenes@...e.cz>
Cc:	mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org, x86@...nel.org, jkosina@...e.cz
Subject: Re: [PATCH RFC tip/perf/core] ftrace/x86: Let dynamic trampolines
 call ops->func even for dynamic fops

On Thu, 2 Apr 2015 13:11:16 +0200 (CEST)
Miroslav Benes <mbenes@...e.cz> wrote:

> On Thu, 5 Mar 2015, Steven Rostedt wrote:
> 
> > On Thu, 5 Mar 2015 16:56:43 +0100 (CET)
> > Miroslav Benes <mbenes@...e.cz> wrote:
> > 
> > > I don't know if you plan to do something about this patch or if you just 
> > > missed it in your e-mail pile. Should I resend it or have you already 
> > > scratched that?
> > 
> > Thanks for the reminder. It was marked as "todo" but fell in the noise.
> > It's worse that I was traveling when you sent this, which makes it more
> > likely to be missed :-/
> > 
> > Anyway, I'm still trying to catch up. If you don't hear from me by next
> > Thursday, please send me another reminder.
> 
> ping...
> 

Thanks for the reminder. I modified your patch to this. Would this work
for you? It only needs to touch the generic ftrace.c file. I kept your
change log though.

-- Steve

>From 00ccbf2f5b7580cd7dcdaeda84828d14f0cba3c9 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
Date: Thu, 19 Feb 2015 15:56:14 +0100
Subject: [PATCH] ftrace: Let dynamic trampolines call ops->func even for
 dynamic fops

Dynamically allocated trampolines call ftrace_ops_get_func to get the
function which they should call. For dynamic fops (FTRACE_OPS_FL_DYNAMIC
flag is set) ftrace_ops_list_func is always returned. This is reasonable
for static trampolines but goes against the main advantage of dynamic
ones, that is avoidance of going through the list of all registered
callbacks for functions that are only being traced by a single callback.

We can fix it by returning ops->func (or recursion safe version) from
ftrace_ops_get_func whenever it is possible for dynamic trampolines.

Note that dynamic trampolines are not allowed for dynamic fops if
CONFIG_PREEMPT=y.

Link: http://lkml.kernel.org/r/alpine.LNX.2.00.1501291023000.25445@pobox.suse.cz
Link: http://lkml.kernel.org/r/1424357773-13536-1-git-send-email-mbenes@suse.cz

Reported-by: Miroslav Benes <mbenes@...e.cz>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 kernel/trace/ftrace.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4f228024055b..d01d238d8ef4 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -249,6 +249,19 @@ static void update_function_graph_func(void);
 static inline void update_function_graph_func(void) { }
 #endif
 
+
+static ftrace_func_t ftrace_ops_get_list_func(struct ftrace_ops *ops)
+{
+	/*
+	 * If this is a dynamic ops or we force list func,
+	 * then it needs to call the list anyway.
+	 */
+	if (ops->flags & FTRACE_OPS_FL_DYNAMIC || FTRACE_FORCE_LIST_FUNC)
+		return ftrace_ops_list_func;
+
+	return ftrace_ops_get_func(ops);
+}
+
 static void update_ftrace_function(void)
 {
 	ftrace_func_t func;
@@ -270,7 +283,7 @@ static void update_ftrace_function(void)
 	 * then have the mcount trampoline call the function directly.
 	 */
 	} else if (ftrace_ops_list->next == &ftrace_list_end) {
-		func = ftrace_ops_get_func(ftrace_ops_list);
+		func = ftrace_ops_get_list_func(ftrace_ops_list);
 
 	} else {
 		/* Just use the default ftrace_ops */
@@ -5209,13 +5222,6 @@ static void ftrace_ops_recurs_func(unsigned long ip, unsigned long parent_ip,
 ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops)
 {
 	/*
-	 * If this is a dynamic ops or we force list func,
-	 * then it needs to call the list anyway.
-	 */
-	if (ops->flags & FTRACE_OPS_FL_DYNAMIC || FTRACE_FORCE_LIST_FUNC)
-		return ftrace_ops_list_func;
-
-	/*
 	 * If the func handles its own recursion, call it directly.
 	 * Otherwise call the recursion protected function that
 	 * will call the ftrace ops function.
-- 
1.8.3.1

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