linux-kernel - Re: [RFC][PATCH 01/18 v2] ftrace: Add hash list to save RCU unsafe functions

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Date:	Tue, 3 Sep 2013 21:51:52 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [RFC][PATCH 01/18 v2] ftrace: Add hash list to save RCU unsafe
 functions

On Tue, 3 Sep 2013 18:24:04 -0700
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:

> On Tue, Sep 03, 2013 at 07:57:05PM -0400, Steven Rostedt wrote:

> > Paul, can I still keep all your acks and reviewed-bys on this?
> 
> Yep, but some questions below.
> 
> 							Thanx, Paul
> 
> > -- Steve
> > 
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 310b727..899c8c1 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -1373,7 +1373,7 @@ ftrace_hash_rec_enable(struct ftrace_ops *ops, int filter_hash);
> > 
> >  static int ftrace_convert_size_to_bits(int size)
> >  {
> > -	int bits;
> > +	int bits = 0;
> > 
> >  	/*
> >  	 * Make the hash size about 1/2 the # found
> > diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
> > index f5a9031..0883069 100644
> > --- a/kernel/trace/trace_functions.c
> > +++ b/kernel/trace/trace_functions.c
> > @@ -561,16 +561,21 @@ static inline int init_func_cmd_traceon(void)
> > 
> >  #ifdef CONFIG_FTRACE_UNSAFE_RCU_CHECKER
> > 
> > +static DEFINE_PER_CPU(int, ftrace_rcu_running);
> >  static atomic_t ftrace_unsafe_rcu_disabled;
> > 
> >  void ftrace_unsafe_rcu_checker_disable(void)
> >  {
> >  	atomic_inc(&ftrace_unsafe_rcu_disabled);
> > +	/* Make sure the update is seen immediately */
> > +	smp_wmb();
> 
> 	smp_mb__after_atomic_inc()?

Yep.

> 
> >  }
> > 
> >  void ftrace_unsafe_rcu_checker_enable(void)
> >  {
> >  	atomic_dec(&ftrace_unsafe_rcu_disabled);
> > +	/* Make sure the update is seen immediately */
> > +	smp_wmb();
> 
> 	smp_mb__after_atomic_dec()?

Yep.

> 
> >  }
> > 
> >  static DEFINE_PER_CPU(unsigned long, ftrace_rcu_func);
> > @@ -588,15 +593,14 @@ static void
> >  ftrace_unsafe_callback(unsigned long ip, unsigned long parent_ip,
> >  		       struct ftrace_ops *op, struct pt_regs *pt_regs)
> >  {
> > -	int bit;
> > -
> > +	/* Make sure we see disabled or not first */
> > +	smp_rmb();
> 
> 	smp_mb__before_atomic_inc()?

Yep.

I'll update it and restart my tests.

Thanks!

-- Steve

> 
> >  	if (atomic_read(&ftrace_unsafe_rcu_disabled))
> >  		return;
> > 
> >  	preempt_disable_notrace();
> > 
> > -	bit = trace_test_and_set_recursion(TRACE_FTRACE_START, TRACE_FTRACE_MAX);
> > -	if (bit < 0)
> > +	if (this_cpu_read(ftrace_rcu_running))
> >  		goto out;
> > 
> >  	if (WARN_ONCE(ftrace_rcu_unsafe(ip),
> > @@ -604,13 +608,15 @@ ftrace_unsafe_callback(unsigned long ip, unsigned long parent_ip,
> >  		      (void *)ip))
> >  		goto out;
> > 
> > +	this_cpu_write(ftrace_rcu_running, 1);
> >  	this_cpu_write(ftrace_rcu_func, ip);
> > +
> >  	/* Should trigger a RCU splat if called from unsafe RCU function */
> >  	rcu_read_lock();
> >  	rcu_read_unlock();
> >  	this_cpu_write(ftrace_rcu_func, 0);
> > 
> > -	trace_clear_recursion(bit);
> > +	this_cpu_write(ftrace_rcu_running, 0);
> >   out:
> >  	preempt_enable_notrace();
> >  }
> > 

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