linux-kernel - Re: [PATCH v7 01/10] tracing: Add support for SOFT

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Date:	Tue, 27 Aug 2013 18:32:16 -0500
From:	Tom Zanussi <tom.zanussi@...ux.intel.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	masami.hiramatsu.pt@...achi.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 01/10] tracing: Add support for SOFT_DISABLE to
 syscall events

On Tue, 2013-08-27 at 16:08 -0400, Steven Rostedt wrote:
> On Tue, 27 Aug 2013 14:40:13 -0500
> Tom Zanussi <tom.zanussi@...ux.intel.com> wrote:
> 
> > @@ -415,9 +429,14 @@ static void unreg_event_syscall_enter(struct ftrace_event_file *file,
> >  		return;
> >  	mutex_lock(&syscall_trace_lock);
> >  	tr->sys_refcount_enter--;
> > -	clear_bit(num, tr->enabled_enter_syscalls);
> > +	rcu_assign_pointer(tr->enter_syscall_files[num], NULL);
> >  	if (!tr->sys_refcount_enter)
> >  		unregister_trace_sys_enter(ftrace_syscall_enter, tr);
> > +	/*
> > +	 * Callers expect the event to be completely disabled on
> > +	 * return, so wait for current handlers to finish.
> > +	 */
> > +	synchronize_sched();
> >  	mutex_unlock(&syscall_trace_lock);
> >  }
> >  
> > @@ -435,7 +454,7 @@ static int reg_event_syscall_exit(struct ftrace_event_file *file,
> >  	if (!tr->sys_refcount_exit)
> >  		ret = register_trace_sys_exit(ftrace_syscall_exit, tr);
> >  	if (!ret) {
> > -		set_bit(num, tr->enabled_exit_syscalls);
> > +		rcu_assign_pointer(tr->exit_syscall_files[num], file);
> >  		tr->sys_refcount_exit++;
> >  	}
> >  	mutex_unlock(&syscall_trace_lock);
> > @@ -453,9 +472,14 @@ static void unreg_event_syscall_exit(struct ftrace_event_file *file,
> >  		return;
> >  	mutex_lock(&syscall_trace_lock);
> >  	tr->sys_refcount_exit--;
> > -	clear_bit(num, tr->enabled_exit_syscalls);
> > +	rcu_assign_pointer(tr->exit_syscall_files[num], NULL);
> >  	if (!tr->sys_refcount_exit)
> >  		unregister_trace_sys_exit(ftrace_syscall_exit, tr);
> > +	/*
> > +	 * Callers expect the event to be completely disabled on
> > +	 * return, so wait for current handlers to finish.
> > +	 */
> > +	synchronize_sched();
> >  	mutex_unlock(&syscall_trace_lock);
> 
> Can we do the synchronize_sched() after the mutex unlock in these two
> places?
> 

Yeah, I think that should be ok and there should be no need to delay
waiters for that mutex - I'll look at moving it out for the next
revision.

Thanks,

Tom

> -- Steve
> 
> 
> >  }
> >  
> 


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