Commit a7c180aa authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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/20141214201609.126831471@goodmis.org"

* 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()
parents 2dbfca5a 0daa2302

Documentation/kernel-parameters.txt

+18 −0
Original line number Diff line number Diff line
@@ -3570,6 +3570,24 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
			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

+7 −0
Original line number Diff line number Diff line
@@ -39,6 +39,12 @@ 
# 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;
@@ -873,6 +879,7 @@ static inline int test_tsk_trace_graph(struct task_struct *tsk) 
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

+4 −0
Original line number Diff line number Diff line
@@ -578,6 +578,10 @@ asmlinkage __visible void __init start_kernel(void) 
		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

+7 −0
Original line number Diff line number Diff line
@@ -623,6 +623,13 @@ static struct ctl_table kern_table[] = { 
		.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

+24 −1
Original line number Diff line number Diff line
@@ -63,6 +63,10 @@ static bool __read_mostly tracing_selftest_running; 
 */

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[] = {

	{ }
@@ -193,6 +197,13 @@ static int __init set_trace_boot_clock(char *str) 
}

__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)

{
@@ -6898,6 +6909,19 @@ out: 
	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)

{

	/*
@@ -6917,6 +6941,5 @@ __init static int clear_boot_tracer(void) 
	return 0;

}



early_initcall(tracer_alloc_buffers);

fs_initcall(tracer_init_debugfs);

late_initcall(clear_boot_tracer);

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