Merge tag 'trace-3.19-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:
"As the merge window is still open, and this code was not as complex as
I thought it might be. I'm pushing this in now.

This will allow Thomas to debug his irq work for 3.20.

This adds two new features:

1) Allow traceopoints to be enabled right after mm_init().

By passing in the trace_event= kernel command line parameter,
tracepoints can be enabled at boot up. For debugging things like
the initialization of interrupts, it is needed to have tracepoints
enabled very early. People have asked about this before and this
has been on my todo list. As it can be helpful for Thomas to debug
his upcoming 3.20 IRQ work, I'm pushing this now. This way he can
add tracepoints into the IRQ set up and have users enable them when
things go wrong.

2) Have the tracepoints printed via printk() (the console) when they
are triggered.

If the irq code locks up or reboots the box, having the tracepoint
output go into the kernel ring buffer is useless for debugging.
But being able to add the tp_printk kernel command line option
along with the trace_event= option will have these tracepoints
printed as they occur, and that can be really useful for debugging
early lock up or reboot problems.

This code is not that intrusive and it passed all my tests. Thomas
tried them out too and it works for his needs.

Link: http://lkml.kernel.org/r/[e-mail]"

* tag 'trace-3.19-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
tracing: Add tp_printk cmdline to have tracepoints go to printk()
tracing: Move enabling tracepoints to just after rcu_init()

Documentation/kernel-parameters.txt

···
 			See also Documentation/trace/ftrace.txt "trace options"
 			section.
 
+	tp_printk[FTRACE]
+			Have the tracepoints sent to printk as well as the
+			tracing ring buffer. This is useful for early boot up
+			where the system hangs or reboots and does not give the
+			option for reading the tracing buffer or performing a
+			ftrace_dump_on_oops.
+
+			To turn off having tracepoints sent to printk,
+			 echo 0 > /proc/sys/kernel/tracepoint_printk
+			Note, echoing 1 into this file without the
+			tracepoint_printk kernel cmdline option has no effect.
+
+			** CAUTION **
+
+			Having tracepoints sent to printk() and activating high
+			frequency tracepoints such as irq or sched, can cause
+			the system to live lock.
+
 	traceoff_on_warning
 			[FTRACE] enable this option to disable tracing when a
 			warning is hit. This turns off "tracing_on". Tracing can

include/linux/ftrace.h

···
 # define FTRACE_FORCE_LIST_FUNC 0
 #endif
 
+/* Main tracing buffer and events set up */
+#ifdef CONFIG_TRACING
+void trace_init(void);
+#else
+static inline void trace_init(void) { }
+#endif
 
 struct module;
 struct ftrace_hash;
···
 enum ftrace_dump_mode;
 
 extern enum ftrace_dump_mode ftrace_dump_on_oops;
+extern int tracepoint_printk;
 
 extern void disable_trace_on_warning(void);
 extern int __disable_trace_on_warning;

init/main.c

···
 		local_irq_disable();
 	idr_init_cache();
 	rcu_init();
+
+	/* trace_printk() and trace points may be used after this */
+	trace_init();
+
 	context_tracking_init();
 	radix_tree_init();
 	/* init some links before init_ISA_irqs() */

kernel/sysctl.c

···
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+	{
+		.procname	= "tracepoint_printk",
+		.data		= &tracepoint_printk,
+		.maxlen		= sizeof(tracepoint_printk),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 #endif
 #ifdef CONFIG_KEXEC
 	{

kernel/trace/trace.c

···
  */
 bool __read_mostly tracing_selftest_disabled;
 
+/* Pipe tracepoints to printk */
+struct trace_iterator *tracepoint_print_iter;
+int tracepoint_printk;
+
 /* For tracers that don't implement custom flags */
 static struct tracer_opt dummy_tracer_opt[] = {
 	{ }
···
 }
 __setup("trace_clock=", set_trace_boot_clock);
 
+static int __init set_tracepoint_printk(char *str)
+{
+	if ((strcmp(str, "=0") != 0 && strcmp(str, "=off") != 0))
+		tracepoint_printk = 1;
+	return 1;
+}
+__setup("tp_printk", set_tracepoint_printk);
 
 unsigned long long ns2usecs(cycle_t nsec)
 {
···
 	return ret;
 }
 
+void __init trace_init(void)
+{
+	if (tracepoint_printk) {
+		tracepoint_print_iter =
+			kmalloc(sizeof(*tracepoint_print_iter), GFP_KERNEL);
+		if (WARN_ON(!tracepoint_print_iter))
+			tracepoint_printk = 0;
+	}
+	tracer_alloc_buffers();
+	init_ftrace_syscalls();
+	trace_event_init();	
+}
+
 __init static int clear_boot_tracer(void)
 {
 	/*
···
 	return 0;
 }
 
-early_initcall(tracer_alloc_buffers);
 fs_initcall(tracer_init_debugfs);
 late_initcall(clear_boot_tracer);

kernel/trace/trace.h

···
 #define perf_ftrace_event_register NULL
 #endif
 
+#ifdef CONFIG_FTRACE_SYSCALLS
+void init_ftrace_syscalls(void);
+#else
+static inline void init_ftrace_syscalls(void) { }
+#endif
+
+#ifdef CONFIG_EVENT_TRACING
+void trace_event_init(void);
+#else
+static inline void __init trace_event_init(void) { }
+#endif
+
+extern struct trace_iterator *tracepoint_print_iter;
+
 #endif /* _LINUX_KERNEL_TRACE_H */

kernel/trace/trace_events.c

···
 }
 EXPORT_SYMBOL_GPL(ftrace_event_buffer_reserve);
 
+static DEFINE_SPINLOCK(tracepoint_iter_lock);
+
+static void output_printk(struct ftrace_event_buffer *fbuffer)
+{
+	struct ftrace_event_call *event_call;
+	struct trace_event *event;
+	unsigned long flags;
+	struct trace_iterator *iter = tracepoint_print_iter;
+
+	if (!iter)
+		return;
+
+	event_call = fbuffer->ftrace_file->event_call;
+	if (!event_call || !event_call->event.funcs ||
+	    !event_call->event.funcs->trace)
+		return;
+
+	event = &fbuffer->ftrace_file->event_call->event;
+
+	spin_lock_irqsave(&tracepoint_iter_lock, flags);
+	trace_seq_init(&iter->seq);
+	iter->ent = fbuffer->entry;
+	event_call->event.funcs->trace(iter, 0, event);
+	trace_seq_putc(&iter->seq, 0);
+	printk("%s", iter->seq.buffer);
+
+	spin_unlock_irqrestore(&tracepoint_iter_lock, flags);
+}
+
 void ftrace_event_buffer_commit(struct ftrace_event_buffer *fbuffer)
 {
+	if (tracepoint_printk)
+		output_printk(fbuffer);
+
 	event_trigger_unlock_commit(fbuffer->ftrace_file, fbuffer->buffer,
 				    fbuffer->event, fbuffer->entry,
 				    fbuffer->flags, fbuffer->pc);
···
 #endif
 	return 0;
 }
-early_initcall(event_trace_memsetup);
-core_initcall(event_trace_enable);
+
+void __init trace_event_init(void)
+{
+	event_trace_memsetup();
+	init_ftrace_syscalls();
+	event_trace_enable();
+}
+
 fs_initcall(event_trace_init);
 
 #ifdef CONFIG_FTRACE_STARTUP_TEST

kernel/trace/trace_syscalls.c

···
 	return (unsigned long)sys_call_table[nr];
 }
 
-static int __init init_ftrace_syscalls(void)
+void __init init_ftrace_syscalls(void)
 {
 	struct syscall_metadata *meta;
 	unsigned long addr;
···
 				    GFP_KERNEL);
 	if (!syscalls_metadata) {
 		WARN_ON(1);
-		return -ENOMEM;
+		return;
 	}
 
 	for (i = 0; i < NR_syscalls; i++) {
···
 		meta->syscall_nr = i;
 		syscalls_metadata[i] = meta;
 	}
-
-	return 0;
 }
-early_initcall(init_ftrace_syscalls);
 
 #ifdef CONFIG_PERF_EVENTS