Date:	Mon, 9 Mar 2009 09:52:20 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Jiaying Zhang <jiayingz@...gle.com>,
	Martin Bligh <mbligh@...gle.com>
Subject: Re: [RFC][PATCH 1/2] tracing/ftrace: syscall tracing
 infrastructure


On Sat, 7 Mar 2009, Frederic Weisbecker wrote:
> +
> +
> +static atomic_t refcount;
> +
> +enum print_line_t
> +print_syscall_enter(struct trace_iterator *iter, int flags)
> +{
> +	struct trace_seq *s = &iter->seq;
> +	struct trace_entry *ent = iter->ent;
> +	struct syscall_trace_enter *trace;
> +	enum syscall_trace_nr syscall;
> +	const struct syscall_trace_entry *entry;
> +	char *str = NULL;
> +	int i, ret;
> +
> +	trace_assign_type(trace, ent);
> +
> +	syscall = trace->nr;
> +
> +	if (!syscall || syscall >= __SYSCALL_TRACE_END)

You still need to print a "\n" otherwise the output of the next line
will start on the current line.

> +		return TRACE_TYPE_HANDLED;
> +
> +	entry = &syscall_trace_entries[syscall];
> +	if (!entry->simple_format) {
> +		ret = entry->output.print(trace->args);
> +		if (!ret)
> +			return TRACE_TYPE_PARTIAL_LINE;
> +		return TRACE_TYPE_HANDLED;
> +	}
> +
> +	ret = trace_seq_printf(s, "syscall %s :", entry->name);
> +	if (!ret)
> +		return TRACE_TYPE_PARTIAL_LINE;
> +
> +	for (i = 0; i < entry->nb_args; i++) {
> +		/*
> +		 * FIXME: the string comes from the user, but on tracing
> +		 * output time, it may have disappeared from the memory.
> +		 * May be better to strdup it on tracing time.
> +		 */
> +		if (entry->output.string_mask & (1 << i)) {
> +			/* 128 is enough for most path */
> +			str = strndup_user((char *)trace->args[i], 128);
> +
> +			/* If it faulted badly, the error shoud have been
> +			 * handled while servicing the syscall, just ignore.
> +			 */
> +			if (str == ERR_PTR(-EFAULT) || str == ERR_PTR(-EINVAL)
> +			    || str == ERR_PTR(-ENOMEM))
> +				return TRACE_TYPE_HANDLED;
> +
> +			ret = trace_seq_printf(s, " %s", str);
> +		} else {
> +			ret = trace_seq_printf(s, " 0x%lx", trace->args[i]);
> +		}
> +		if (!ret)
> +			goto end_partial;
> +	}
> +	if (!trace_seq_printf(s, "\n"))
> +		goto end_partial;
> +
> +	kfree(str);
> +	return TRACE_TYPE_HANDLED;
> +
> +end_partial:
> +	kfree(str);
> +	return TRACE_TYPE_PARTIAL_LINE;
> +}
> +
> +enum print_line_t
> +print_syscall_exit(struct trace_iterator *iter, int flags)
> +{
> +	struct trace_seq *s = &iter->seq;
> +	struct trace_entry *ent = iter->ent;
> +	struct syscall_trace_exit *trace;
> +	enum syscall_trace_nr syscall;
> +	const struct syscall_trace_entry *entry;
> +	int ret;
> +
> +	trace_assign_type(trace, ent);
> +
> +	syscall = trace->nr;
> +
> +	if (!syscall || syscall >= __SYSCALL_TRACE_END)
> +		return TRACE_TYPE_HANDLED;
> +
> +	entry = &syscall_trace_entries[syscall];
> +
> +	ret = trace_seq_printf(s, "syscall %s -> 0x%lx\n", entry->name,
> +				trace->ret);
> +	if (!ret)
> +		return TRACE_TYPE_PARTIAL_LINE;
> +
> +	return TRACE_TYPE_HANDLED;
> +}
> +
> +void start_ftrace_syscalls(void)
> +{
> +	unsigned long flags;
> +	struct task_struct *g, *t;
> +
> +	if (atomic_inc_return(&refcount) != 1)
> +		goto out;
> +
> +	read_lock_irqsave(&tasklist_lock, flags);
> +
> +	do_each_thread(g, t) {
> +		set_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
> +	} while_each_thread(g, t);
> +
> +	read_unlock_irqrestore(&tasklist_lock, flags);
> +
> +	return;
> +out:
> +	atomic_dec(&refcount);
> +}
> +
> +void stop_ftrace_syscalls(void)
> +{
> +	unsigned long flags;
> +	struct task_struct *g, *t;
> +
> +	if (atomic_dec_return(&refcount))
> +		return;
> +
> +	read_lock_irqsave(&tasklist_lock, flags);
> +
> +	do_each_thread(g, t) {
> +		clear_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
> +	} while_each_thread(g, t);
> +
> +	read_unlock_irqrestore(&tasklist_lock, flags);
> +}
> +
> +void ftrace_syscall_enter(struct pt_regs *regs)
> +{
> +	struct trace_array *tr = __get_global_trace();
> +	struct syscall_trace_enter *entry;
> +	const struct syscall_trace_entry *sys_data;
> +	struct ring_buffer_event *event;
> +	struct trace_array_cpu *data;
> +	int size;
> +	int syscall_nr;
> +	int nr_offset;
> +	int cpu;
> +
> +	syscall_nr = syscall_get_nr(current, regs);
> +	nr_offset = arch_syscall_trace_nr[syscall_nr];
> +	if (!nr_offset || nr_offset >= __SYSCALL_TRACE_END)
> +		return;
> +
> +	cpu = raw_smp_processor_id();
> +	data = tr->data[cpu];
> +
> +	if (unlikely(atomic_read(&data->disabled)))
> +		return;
> +
> +	sys_data = &syscall_trace_entries[nr_offset];
> +	size = sizeof(*entry) + sizeof(unsigned long) * sys_data->nb_args;
> +
> +	event = trace_buffer_lock_reserve(tr, TRACE_SYSCALL_ENTER, size, 0, 0);
> +	if (!event)
> +		return;
> +
> +	entry = ring_buffer_event_data(event);
> +	entry->nr = nr_offset;
> +	syscall_get_arguments(current, regs, 0, sys_data->nb_args, entry->args);
> +
> +	ring_buffer_unlock_commit(tr->buffer, event);

BTW, you should always use the matching lock. Above you used 
trace_buffer_lock_reserve, and here you use ring_buffer_unlock_commit. 
This may not work in the future. There is a trace_buffer_unlock_commit 
too.

But you are going to change these to trace_current_buffer_lock_reserve and 
trace_current_buffer_unlock_commit anyway ;-)


> +	trace_wake_up();
> +}
> +
> +void ftrace_syscall_exit(struct pt_regs *regs)
> +{
> +	struct trace_array *tr = __get_global_trace();
> +	struct syscall_trace_exit *entry;
> +	const struct syscall_trace_entry *sys_data;
> +	struct ring_buffer_event *event;
> +	struct trace_array_cpu *data;
> +	int syscall_nr;
> +	int nr_offset;
> +	int cpu;
> +
> +	syscall_nr = syscall_get_nr(current, regs);
> +	nr_offset = arch_syscall_trace_nr[syscall_nr];
> +	if (!nr_offset || nr_offset >= __SYSCALL_TRACE_END)
> +		return;
> +
> +	cpu = raw_smp_processor_id();
> +	data = tr->data[cpu];
> +
> +	if (unlikely(atomic_read(&data->disabled)))
> +		return;
> +
> +	sys_data = &syscall_trace_entries[nr_offset];
> +
> +	event = trace_buffer_lock_reserve(tr, TRACE_SYSCALL_EXIT,
> +				sizeof(*entry), 0, 0);
> +	if (!event)
> +		return;
> +
> +	entry = ring_buffer_event_data(event);
> +	entry->nr = nr_offset;
> +	entry->ret = syscall_get_return_value(current, regs);
> +
> +	ring_buffer_unlock_commit(tr->buffer, event);

Same here.

-- Steve

> +	trace_wake_up();
> +}
> +
> +static int init_syscall_tracer(struct trace_array *tr)
> +{
> +	start_ftrace_syscalls();
> +
> +	return 0;
> +}
> +
> +static void reset_syscall_tracer(struct trace_array *tr)
> +{
> +	stop_ftrace_syscalls();
> +}
> +
> +static struct trace_event syscall_enter_event = {
> +	.type	 	= TRACE_SYSCALL_ENTER,
> +	.trace		= print_syscall_enter,
> +};
> +
> +static struct trace_event syscall_exit_event = {
> +	.type	 	= TRACE_SYSCALL_EXIT,
> +	.trace		= print_syscall_exit,
> +};
> +
> +static struct tracer syscall_tracer __read_mostly = {
> +	.name	     	= "syscall",
> +	.init		= init_syscall_tracer,
> +	.reset		= reset_syscall_tracer
> +};
> +
> +__init int register_ftrace_syscalls(void)
> +{
> +	int ret;
> +
> +	ret = register_ftrace_event(&syscall_enter_event);
> +	if (!ret) {
> +		printk(KERN_WARNING "event %d failed to register\n",
> +		       syscall_enter_event.type);
> +		WARN_ON_ONCE(1);
> +	}
> +
> +	ret = register_ftrace_event(&syscall_exit_event);
> +	if (!ret) {
> +		printk(KERN_WARNING "event %d failed to register\n",
> +		       syscall_exit_event.type);
> +		WARN_ON_ONCE(1);
> +	}
> +
> +	return register_tracer(&syscall_tracer);
> +}
> +device_initcall(register_ftrace_syscalls);
> -- 
> 1.6.1
> 
> 
> 
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