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

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

(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.)

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);
> +	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:
> 


-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com