Re: [PATCH] tracing/uprobes: Support ftrace_event_file base multibuffer

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Fri, Jun 14, 2013 at 11:31:58AM -0400, Steven Rostedt wrote:
> On Fri, 2013-06-14 at 22:21 +0900, Masami Hiramatsu wrote:
> > (2013/06/14 10:44), zhangwei(Jovi) wrote:
> > > Support multi-buffer on uprobe-based dynamic events by
> > > using ftrace_event_file.
> > > 
> > > The code change is based on kprobe-based dynamic events
> > > multibuffer support work commited by Masami(commit 41a7dd420c)
> > 
> > I'm not so sure that rcu_dereference_raw() can ensure the safety
> > of accessing pointer in uprobe handler. ( since kprobes disables
> > irq and preempt, it could use rcu.)
> 
> Correct.
> 
> > 
> > Srikar, Oleg, could you check that?
> > 
> > Thank you,
> > 
> > > 
> > > Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
> > > Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> > > Cc: Frederic Weisbecker <fweisbec@gmail.com>
> > > Cc: Oleg Nesterov <oleg@redhat.com>
> > > Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> > > ---
> > >  kernel/trace/trace_uprobe.c |  183 +++++++++++++++++++++++++++++++++++++------
> > >  1 file changed, 161 insertions(+), 22 deletions(-)
> > > 
> > > diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> > > index d5d0cd3..31f08d6 100644
> > > --- a/kernel/trace/trace_uprobe.c
> > > +++ b/kernel/trace/trace_uprobe.c
> > > @@ -53,6 +53,7 @@ struct trace_uprobe {
> > >  	struct list_head		list;
> > >  	struct ftrace_event_class	class;
> > >  	struct ftrace_event_call	call;
> > > +	struct ftrace_event_file * __rcu *files;
> > >  	struct trace_uprobe_filter	filter;
> > >  	struct uprobe_consumer		consumer;
> > >  	struct inode			*inode;
> > > @@ -513,7 +514,8 @@ static const struct file_operations uprobe_profile_ops = {
> > >  };
> > > 
> > >  static void uprobe_trace_print(struct trace_uprobe *tu,
> > > -				unsigned long func, struct pt_regs *regs)
> > > +				unsigned long func, struct pt_regs *regs,
> > > +				struct ftrace_event_file *ftrace_file)
> > >  {
> > >  	struct uprobe_trace_entry_head *entry;
> > >  	struct ring_buffer_event *event;
> > > @@ -522,9 +524,15 @@ static void uprobe_trace_print(struct trace_uprobe *tu,
> > >  	int size, i;
> > >  	struct ftrace_event_call *call = &tu->call;
> > > 
> > > +	WARN_ON(call != ftrace_file->event_call);
> > > +
> > > +	if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &ftrace_file->flags))
> > > +		return;
> > > +
> > >  	size = SIZEOF_TRACE_ENTRY(is_ret_probe(tu));
> > > -	event = trace_current_buffer_lock_reserve(&buffer, call->event.type,
> > > -						  size + tu->size, 0, 0);
> > > +	event = trace_event_buffer_lock_reserve(&buffer, ftrace_file,
> > > +						call->event.type,
> > > +						size + tu->size, 0, 0);
> > >  	if (!event)
> > >  		return;
> > > 
> > > @@ -548,15 +556,35 @@ static void uprobe_trace_print(struct trace_uprobe *tu,
> > >  /* uprobe handler */
> > >  static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
> > >  {
> > > -	if (!is_ret_probe(tu))
> > > -		uprobe_trace_print(tu, 0, regs);
> > > +	struct ftrace_event_file **file;
> > > +
> > > +	if (is_ret_probe(tu))
> > > +		return 0;
> > > +
> > > +	file = rcu_dereference_raw(tu->files);
> 
> Why are you using rcu_dereference_raw() and not rcu_dereference(). The
> _raw() is a bit special, and unless you know what you are doing with RCU
> here, don't use it.
> 
> As I see you using rcu_dereference_raw() all over this patch, along with
> mutexes, I believe that you are not using RCU correctly here.

If irqs and preempt are disabled, I suggest using rcu_dereference_sched().
That is what it is there for.  ;-)

							Thanx, Paul

> -- Steve
> 
> > > +	if (unlikely(!file))
> > > +		return 0;
> > > +
> > > +	while (*file) {
> > > +		uprobe_trace_print(tu, 0, regs, *file);
> > > +		file++;
> > > +	}
> > > +
> > >  	return 0;
> > >  }
> > > 
> > >  static void uretprobe_trace_func(struct trace_uprobe *tu, unsigned long func,
> > >  				struct pt_regs *regs)
> > >  {
> > > -	uprobe_trace_print(tu, func, regs);
> > > +	struct ftrace_event_file **file = rcu_dereference_raw(tu->files);
> > > +
> > > +	if (unlikely(!file))
> > > +		return;
> > > +
> > > +	while (*file) {
> > > +		uprobe_trace_print(tu, func, regs, *file);
> > > +		file++;
> > > +	}
> > >  }
> > > 
> > >  /* Event entry printers */
> > > @@ -597,6 +625,26 @@ partial:
> > >  	return TRACE_TYPE_PARTIAL_LINE;
> > >  }
> > > 
> > > +
> > > +static int trace_uprobe_nr_files(struct trace_uprobe *tu)
> > > +{
> > > +	struct ftrace_event_file **file;
> > > +	int ret = 0;
> > > +
> > > +	/*
> > > +	 * Since all tu->files updater is protected by uprobe_enable_lock,
> > > +	 * we don't need to lock an rcu_read_lock.
> > > +	 */
> > > +	file = rcu_dereference_raw(tu->files);
> > > +	if (file)
> > > +		while (*(file++))
> > > +			ret++;
> > > +
> > > +	return ret;
> > > +}
> > > +
> > > +static DEFINE_MUTEX(uprobe_enable_lock);
> > > +
> > >  static inline bool is_trace_uprobe_enabled(struct trace_uprobe *tu)
> > >  {
> > >  	return tu->flags & (TP_FLAG_TRACE | TP_FLAG_PROFILE);
> > > @@ -607,33 +655,123 @@ typedef bool (*filter_func_t)(struct uprobe_consumer *self,
> > >  				struct mm_struct *mm);
> > > 
> > >  static int
> > > -probe_event_enable(struct trace_uprobe *tu, int flag, filter_func_t filter)
> > > +probe_event_enable(struct trace_uprobe *tu, struct ftrace_event_file *file,
> > > +		   filter_func_t filter)
> > >  {
> > > +	int enabled = 0;
> > >  	int ret = 0;
> > > 
> > > +	mutex_lock(&uprobe_enable_lock);
> > > +
> > >  	if (is_trace_uprobe_enabled(tu))
> > > -		return -EINTR;
> > > +		enabled = 1;
> > > +
> > > +	if (file) {
> > > +		struct ftrace_event_file **new, **old;
> > > +		int n = trace_uprobe_nr_files(tu);
> > > +
> > > +		old = rcu_dereference_raw(tu->files);
> > > +		/* 1 is for new one and 1 is for stopper */
> > > +		new = kzalloc((n + 2) * sizeof(struct ftrace_event_file *),
> > > +			      GFP_KERNEL);
> > > +		if (!new) {
> > > +			ret = -ENOMEM;
> > > +			goto out_unlock;
> > > +		}
> > > +		memcpy(new, old, n * sizeof(struct ftrace_event_file *));
> > > +		new[n] = file;
> > > +		/* The last one keeps a NULL */
> > > +
> > > +		rcu_assign_pointer(tu->files, new);
> > > +		tu->flags |= TP_FLAG_TRACE;
> > > +
> > > +		if (old) {
> > > +			/* Make sure the probe is done with old files */
> > > +			synchronize_sched();
> > > +			kfree(old);
> > > +		}
> > > +	} else
> > > +		tu->flags |= TP_FLAG_PROFILE;
> > > 
> > >  	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
> > > 
> > > -	tu->flags |= flag;
> > > -	tu->consumer.filter = filter;
> > > -	ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> > > -	if (ret)
> > > -		tu->flags &= ~flag;
> > > +	if (!enabled) {
> > > +		tu->consumer.filter = filter;
> > > +		ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> > > +		if (ret)
> > > +			tu->flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
> > > +	}
> > > 
> > > + out_unlock:
> > > +	mutex_unlock(&uprobe_enable_lock);
> > >  	return ret;
> > >  }
> > > 
> > > -static void probe_event_disable(struct trace_uprobe *tu, int flag)
> > > +static int
> > > +trace_uprobe_file_index(struct trace_uprobe *tu, struct ftrace_event_file *file)
> > >  {
> > > -	if (!is_trace_uprobe_enabled(tu))
> > > -		return;
> > > +	struct ftrace_event_file **files;
> > > +	int i;
> > > +
> > > +	/*
> > > +	 * Since all tu->files updater is protected by uprobe_enable_lock,
> > > +	 * we don't need to lock an rcu_read_lock.
> > > +	 */
> > > +	files = rcu_dereference_raw(tu->files);
> > > +	if (files) {
> > > +		for (i = 0; files[i]; i++)
> > > +			if (files[i] == file)
> > > +				return i;
> > > +	}
> > > +
> > > +	return -1;
> > > +}
> > > +
> > > +static void
> > > +probe_event_disable(struct trace_uprobe *tu, struct ftrace_event_file *file)
> > > +{
> > > +	mutex_lock(&uprobe_enable_lock);
> > > +
> > > +	if (file) {
> > > +		struct ftrace_event_file **new, **old;
> > > +		int n = trace_uprobe_nr_files(tu);
> > > +		int i, j;
> > > +
> > > +		old = rcu_dereference_raw(tu->files);
> > > +		if (n == 0 || trace_uprobe_file_index(tu, file) < 0)
> > > +			goto out_unlock;
> > > +
> > > +		if (n == 1) {	/* Remove the last file */
> > > +			tu->flags &= ~TP_FLAG_TRACE;
> > > +			new = NULL;
> > > +		} else {
> > > +			new = kzalloc(n * sizeof(struct ftrace_event_file *),
> > > +				      GFP_KERNEL);
> > > +			if (!new)
> > > +				goto out_unlock;
> > > +
> > > +			/* This copy & check loop copies the NULL stopper too */
> > > +			for (i = 0, j = 0; j < n && i < n + 1; i++)
> > > +				if (old[i] != file)
> > > +					new[j++] = old[i];
> > > +		}
> > > +
> > > +		rcu_assign_pointer(tu->files, new);
> > > +
> > > +		/* Make sure the probe is done with old files */
> > > +		synchronize_sched();
> > > +		kfree(old);
> > > +	} else
> > > +		tu->flags &= ~TP_FLAG_PROFILE;
> > > +
> > > 
> > >  	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
> > > 
> > > -	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> > > -	tu->flags &= ~flag;
> > > +	if (!is_trace_uprobe_enabled(tu))
> > > +		uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> > > +
> > > + out_unlock:
> > > +	mutex_unlock(&uprobe_enable_lock);
> > >  }
> > > 
> > >  static int uprobe_event_define_fields(struct ftrace_event_call *event_call)
> > > @@ -869,21 +1007,22 @@ static
> > >  int trace_uprobe_register(struct ftrace_event_call *event, enum trace_reg type, void *data)
> > >  {
> > >  	struct trace_uprobe *tu = event->data;
> > > +	struct ftrace_event_file *file = data;
> > > 
> > >  	switch (type) {
> > >  	case TRACE_REG_REGISTER:
> > > -		return probe_event_enable(tu, TP_FLAG_TRACE, NULL);
> > > +		return probe_event_enable(tu, file, NULL);
> > > 
> > >  	case TRACE_REG_UNREGISTER:
> > > -		probe_event_disable(tu, TP_FLAG_TRACE);
> > > +		probe_event_disable(tu, file);
> > >  		return 0;
> > > 
> > >  #ifdef CONFIG_PERF_EVENTS
> > >  	case TRACE_REG_PERF_REGISTER:
> > > -		return probe_event_enable(tu, TP_FLAG_PROFILE, uprobe_perf_filter);
> > > +		return probe_event_enable(tu, NULL, uprobe_perf_filter);
> > > 
> > >  	case TRACE_REG_PERF_UNREGISTER:
> > > -		probe_event_disable(tu, TP_FLAG_PROFILE);
> > > +		probe_event_disable(tu, NULL);
> > >  		return 0;
> > > 
> > >  	case TRACE_REG_PERF_OPEN:
> > > 
> > 
> > 
> 
>