linux-kernel - Re: [BUG] ftrace: available_filter_functions empty after unloading module

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Date:	Thu, 13 Dec 2012 12:08:05 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Piotr Haber <phaber@...adcom.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] ftrace: available_filter_functions empty after unloading
 module

On Thu, 2012-12-13 at 08:34 -0500, Steven Rostedt wrote:
> On Mon, 2012-12-10 at 12:45 +0100, Piotr Haber wrote:
> 
> > > So you unloaded a module that you were tracing, correct? Hmm, the
> > > warning that you hit was an accounting error. The accounting of what
> > > functions are traced and what isn't. For some reason it tried to disable
> > > a function that wasn't being traced.
> > Yes, it happens when i unload a module that i traced before
> > 
> > > Can you easily reproduce this? If so, can you give my your .config and
> > > the steps you used to trigger it.
> > Not 100% but it happens often enough to be annoying
> > Attached is the config
> > As for reproduction, i load the brcmsmac module, add all it symbols to
> > set_ftrace_filter, associate with AP and unload the module
> > nothing fancy, i use 'function' tracer
> 
> Thanks, I'll see if I can reproduce it.
> 

I'm having trouble reproducing. Can you apply the below patch and try to
reproduce it. And then show me the contents
of /debug/tracing/enabled_functions.

Thanks,

-- Steve

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4451aa3..e069227 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2390,9 +2390,6 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
 	struct ftrace_ops *ops = iter->ops;
 	struct dyn_ftrace *rec = NULL;
 
-	if (unlikely(ftrace_disabled))
-		return NULL;
-
 	if (iter->flags & FTRACE_ITER_HASH)
 		return t_hash_next(m, pos);
 
@@ -2449,9 +2446,6 @@ static void *t_start(struct seq_file *m, loff_t *pos)
 
 	mutex_lock(&ftrace_lock);
 
-	if (unlikely(ftrace_disabled))
-		return NULL;
-
 	/*
 	 * If an lseek was done, then reset and start from beginning.
 	 */
@@ -2557,9 +2551,6 @@ ftrace_enabled_open(struct inode *inode, struct file *file)
 {
 	struct ftrace_iterator *iter;
 
-	if (unlikely(ftrace_disabled))
-		return -ENODEV;
-
 	iter = __seq_open_private(file, &show_ftrace_seq_ops, sizeof(*iter));
 	if (iter) {
 		iter->pg = ftrace_pages_start;


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