This release cycle is rather small. Just a few fixes to tracing.

The big change is the addition of the hwlat tracer. It not only detects
 SMIs, but also other latency that's caused by the hardware. I have detected
 some latency from large boxes having bus contention.
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Merge tag 'trace-v4.9' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:
 "This release cycle is rather small.  Just a few fixes to tracing.

  The big change is the addition of the hwlat tracer. It not only
  detects SMIs, but also other latency that's caused by the hardware. I
  have detected some latency from large boxes having bus contention"

* tag 'trace-v4.9' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Call traceoff trigger after event is recorded
  ftrace/scripts: Add helper script to bisect function tracing problem functions
  tracing: Have max_latency be defined for HWLAT_TRACER as well
  tracing: Add NMI tracing in hwlat detector
  tracing: Have hwlat trace migrate across tracing_cpumask CPUs
  tracing: Add documentation for hwlat_detector tracer
  tracing: Added hardware latency tracer
  ftrace: Access ret_stack->subtime only in the function profiler
  function_graph: Handle TRACE_BPUTS in print_graph_comment
  tracing/uprobe: Drop isdigit() check in create_trace_uprobe

Documentation/trace/ftrace.txt

@@ -858,11 +858,11 @@ x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
 	       When enabled, it will account time the task has been
 	       scheduled out as part of the function call.
 
-  graph-time - When running function graph tracer, to include the
+  graph-time - When running function profiler with function graph tracer,
-  	       time to call nested functions. When this is not set,
+	       to include the time to call nested functions. When this is
-	       the time reported for the function will only include
+	       not set, the time reported for the function will only
-	       the time the function itself executed for, not the time
+	       include the time the function itself executed for, not the
-	       for functions that it called.
+	       time for functions that it called.
 
   record-cmd - When any event or tracer is enabled, a hook is enabled
   	       in the sched_switch trace point to fill comm cache

Documentation/trace/hwlat_detector.txt

@@ -0,0 +1,79 @@
+Introduction:
+-------------
+
+The tracer hwlat_detector is a special purpose tracer that is used to
+detect large system latencies induced by the behavior of certain underlying
+hardware or firmware, independent of Linux itself. The code was developed
+originally to detect SMIs (System Management Interrupts) on x86 systems,
+however there is nothing x86 specific about this patchset. It was
+originally written for use by the "RT" patch since the Real Time
+kernel is highly latency sensitive.
+
+SMIs are not serviced by the Linux kernel, which means that it does not
+even know that they are occuring. SMIs are instead set up by BIOS code
+and are serviced by BIOS code, usually for "critical" events such as
+management of thermal sensors and fans. Sometimes though, SMIs are used for
+other tasks and those tasks can spend an inordinate amount of time in the
+handler (sometimes measured in milliseconds). Obviously this is a problem if
+you are trying to keep event service latencies down in the microsecond range.
+
+The hardware latency detector works by hogging one of the cpus for configurable
+amounts of time (with interrupts disabled), polling the CPU Time Stamp Counter
+for some period, then looking for gaps in the TSC data. Any gap indicates a
+time when the polling was interrupted and since the interrupts are disabled,
+the only thing that could do that would be an SMI or other hardware hiccup
+(or an NMI, but those can be tracked).
+
+Note that the hwlat detector should *NEVER* be used in a production environment.
+It is intended to be run manually to determine if the hardware platform has a
+problem with long system firmware service routines.
+
+Usage:
+------
+
+Write the ASCII text "hwlat" into the current_tracer file of the tracing system
+(mounted at /sys/kernel/tracing or /sys/kernel/tracing). It is possible to
+redefine the threshold in microseconds (us) above which latency spikes will
+be taken into account.
+
+Example:
+
+	# echo hwlat > /sys/kernel/tracing/current_tracer
+	# echo 100 > /sys/kernel/tracing/tracing_thresh
+
+The /sys/kernel/tracing/hwlat_detector interface contains the following files:
+
+width			- time period to sample with CPUs held (usecs)
+			  must be less than the total window size (enforced)
+window			- total period of sampling, width being inside (usecs)
+
+By default the width is set to 500,000 and window to 1,000,000, meaning that
+for every 1,000,000 usecs (1s) the hwlat detector will spin for 500,000 usecs
+(0.5s). If tracing_thresh contains zero when hwlat tracer is enabled, it will
+change to a default of 10 usecs. If any latencies that exceed the threshold is
+observed then the data will be written to the tracing ring buffer.
+
+The minimum sleep time between periods is 1 millisecond. Even if width
+is less than 1 millisecond apart from window, to allow the system to not
+be totally starved.
+
+If tracing_thresh was zero when hwlat detector was started, it will be set
+back to zero if another tracer is loaded. Note, the last value in
+tracing_thresh that hwlat detector had will be saved and this value will
+be restored in tracing_thresh if it is still zero when hwlat detector is
+started again.
+
+The following tracing directory files are used by the hwlat_detector:
+
+in /sys/kernel/tracing:
+
+ tracing_threshold	- minimum latency value to be considered (usecs)
+ tracing_max_latency	- maximum hardware latency actually observed (usecs)
+ tracing_cpumask	- the CPUs to move the hwlat thread across
+ hwlat_detector/width	- specified amount of time to spin within window (usecs)
+ hwlat_detector/window	- amount of time between (width) runs (usecs)
+
+The hwlat detector's kernel thread will migrate across each CPU specified in
+tracing_cpumask between each window. To limit the migration, either modify
+tracing_cpumask, or modify the hwlat kernel thread (named [hwlatd]) CPU
+affinity directly, and the migration will stop.

arch/sh/kernel/ftrace.c

@@ -139,7 +139,7 @@ static void ftrace_mod_code(void)
 		clear_mod_flag();
 }
 
-void ftrace_nmi_enter(void)
+void arch_ftrace_nmi_enter(void)
 {
 	if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
 		smp_rmb();
@@ -150,7 +150,7 @@ void ftrace_nmi_enter(void)
 	smp_mb();
 }
 
-void ftrace_nmi_exit(void)
+void arch_ftrace_nmi_exit(void)
 {
 	/* Finish all executions before clearing nmi_running */
 	smp_mb();

include/linux/ftrace.h

@@ -794,7 +794,9 @@ struct ftrace_ret_stack {
 	unsigned long ret;
 	unsigned long func;
 	unsigned long long calltime;
+#ifdef CONFIG_FUNCTION_PROFILER
 	unsigned long long subtime;
+#endif
 #ifdef HAVE_FUNCTION_GRAPH_FP_TEST
 	unsigned long fp;
 #endif

include/linux/ftrace_irq.h

@@ -3,11 +3,34 @@
 
 
 #ifdef CONFIG_FTRACE_NMI_ENTER
-extern void ftrace_nmi_enter(void);
+extern void arch_ftrace_nmi_enter(void);
-extern void ftrace_nmi_exit(void);
+extern void arch_ftrace_nmi_exit(void);
 #else
-static inline void ftrace_nmi_enter(void) { }
+static inline void arch_ftrace_nmi_enter(void) { }
-static inline void ftrace_nmi_exit(void) { }
+static inline void arch_ftrace_nmi_exit(void) { }
 #endif
 
+#ifdef CONFIG_HWLAT_TRACER
+extern bool trace_hwlat_callback_enabled;
+extern void trace_hwlat_callback(bool enter);
+#endif
+
+static inline void ftrace_nmi_enter(void)
+{
+#ifdef CONFIG_HWLAT_TRACER
+	if (trace_hwlat_callback_enabled)
+		trace_hwlat_callback(true);
+#endif
+	arch_ftrace_nmi_enter();
+}
+
+static inline void ftrace_nmi_exit(void)
+{
+	arch_ftrace_nmi_exit();
+#ifdef CONFIG_HWLAT_TRACER
+	if (trace_hwlat_callback_enabled)
+		trace_hwlat_callback(false);
+#endif
+}
+
 #endif /* _LINUX_FTRACE_IRQ_H */

kernel/trace/Kconfig

@@ -216,6 +216,41 @@ config SCHED_TRACER
 	  This tracer tracks the latency of the highest priority task
 	  to be scheduled in, starting from the point it has woken up.
 
+config HWLAT_TRACER
+	bool "Tracer to detect hardware latencies (like SMIs)"
+	select GENERIC_TRACER
+	help
+	 This tracer, when enabled will create one or more kernel threads,
+	 depening on what the cpumask file is set to, which each thread
+	 spinning in a loop looking for interruptions caused by
+	 something other than the kernel. For example, if a
+	 System Management Interrupt (SMI) takes a noticeable amount of
+	 time, this tracer will detect it. This is useful for testing
+	 if a system is reliable for Real Time tasks.
+
+	 Some files are created in the tracing directory when this
+	 is enabled:
+
+	   hwlat_detector/width   - time in usecs for how long to spin for
+	   hwlat_detector/window  - time in usecs between the start of each
+				     iteration
+
+	 A kernel thread is created that will spin with interrupts disabled
+	 for "width" microseconds in every "widow" cycle. It will not spin
+	 for "window - width" microseconds, where the system can
+	 continue to operate.
+
+	 The output will appear in the trace and trace_pipe files.
+
+	 When the tracer is not running, it has no affect on the system,
+	 but when it is running, it can cause the system to be
+	 periodically non responsive. Do not run this tracer on a
+	 production system.
+
+	 To enable this tracer, echo in "hwlat" into the current_tracer
+	 file. Every time a latency is greater than tracing_thresh, it will
+	 be recorded into the ring buffer.
+
 config ENABLE_DEFAULT_TRACERS
 	bool "Trace process context switches and events"
 	depends on !GENERIC_TRACER

kernel/trace/Makefile

@@ -41,6 +41,7 @@ obj-$(CONFIG_FUNCTION_TRACER) += trace_functions.o
 obj-$(CONFIG_IRQSOFF_TRACER) += trace_irqsoff.o
 obj-$(CONFIG_PREEMPT_TRACER) += trace_irqsoff.o
 obj-$(CONFIG_SCHED_TRACER) += trace_sched_wakeup.o
+obj-$(CONFIG_HWLAT_TRACER) += trace_hwlat.o
 obj-$(CONFIG_NOP_TRACER) += trace_nop.o
 obj-$(CONFIG_STACK_TRACER) += trace_stack.o
 obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o

kernel/trace/ftrace.c

@@ -872,7 +872,13 @@ function_profile_call(unsigned long ip, unsigned long parent_ip,
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 static int profile_graph_entry(struct ftrace_graph_ent *trace)
 {
+	int index = trace->depth;
+
 	function_profile_call(trace->func, 0, NULL, NULL);
+
+	if (index >= 0 && index < FTRACE_RETFUNC_DEPTH)
+		current->ret_stack[index].subtime = 0;
+
 	return 1;
 }
 

kernel/trace/trace.c

@@ -1047,7 +1047,7 @@ void disable_trace_on_warning(void)
  *
  * Shows real state of the ring buffer if it is enabled or not.
  */
-static int tracer_tracing_is_on(struct trace_array *tr)
+int tracer_tracing_is_on(struct trace_array *tr)
 {
 	if (tr->trace_buffer.buffer)
 		return ring_buffer_record_is_on(tr->trace_buffer.buffer);
@@ -4969,7 +4969,7 @@ out:
 	return ret;
 }
 
-#ifdef CONFIG_TRACER_MAX_TRACE
+#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
 
 static ssize_t
 tracing_max_lat_read(struct file *filp, char __user *ubuf,
@@ -5892,7 +5892,7 @@ static const struct file_operations tracing_thresh_fops = {
 	.llseek		= generic_file_llseek,
 };
 
-#ifdef CONFIG_TRACER_MAX_TRACE
+#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
 static const struct file_operations tracing_max_lat_fops = {
 	.open		= tracing_open_generic,
 	.read		= tracing_max_lat_read,
@@ -7222,7 +7222,7 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
 
 	create_trace_options_dir(tr);
 
-#ifdef CONFIG_TRACER_MAX_TRACE
+#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
 	trace_create_file("tracing_max_latency", 0644, d_tracer,
 			&tr->max_latency, &tracing_max_lat_fops);
 #endif

kernel/trace/trace.h

@@ -38,6 +38,7 @@ enum trace_type {
 	TRACE_USER_STACK,
 	TRACE_BLK,
 	TRACE_BPUTS,
+	TRACE_HWLAT,
 
 	__TRACE_LAST_TYPE,
 };
@@ -213,6 +214,8 @@ struct trace_array {
 	 */
 	struct trace_buffer	max_buffer;
 	bool			allocated_snapshot;
+#endif
+#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
 	unsigned long		max_latency;
 #endif
 	struct trace_pid_list	__rcu *filtered_pids;
@@ -326,6 +329,7 @@ extern void __ftrace_bad_type(void);
 		IF_ASSIGN(var, ent, struct print_entry, TRACE_PRINT);	\
 		IF_ASSIGN(var, ent, struct bprint_entry, TRACE_BPRINT);	\
 		IF_ASSIGN(var, ent, struct bputs_entry, TRACE_BPUTS);	\
+		IF_ASSIGN(var, ent, struct hwlat_entry, TRACE_HWLAT);	\
 		IF_ASSIGN(var, ent, struct trace_mmiotrace_rw,		\
 			  TRACE_MMIO_RW);				\
 		IF_ASSIGN(var, ent, struct trace_mmiotrace_map,		\
@@ -571,6 +575,7 @@ void tracing_reset_current(int cpu);
 void tracing_reset_all_online_cpus(void);
 int tracing_open_generic(struct inode *inode, struct file *filp);
 bool tracing_is_disabled(void);
+int tracer_tracing_is_on(struct trace_array *tr);
 struct dentry *trace_create_file(const char *name,
 				 umode_t mode,
 				 struct dentry *parent,

kernel/trace/trace_entries.h

@@ -322,3 +322,30 @@ FTRACE_ENTRY(branch, trace_branch,
 	FILTER_OTHER
 );
 
+
+FTRACE_ENTRY(hwlat, hwlat_entry,
+
+	TRACE_HWLAT,
+
+	F_STRUCT(
+		__field(	u64,			duration	)
+		__field(	u64,			outer_duration	)
+		__field(	u64,			nmi_total_ts	)
+		__field_struct( struct timespec,	timestamp	)
+		__field_desc(	long,	timestamp,	tv_sec		)
+		__field_desc(	long,	timestamp,	tv_nsec		)
+		__field(	unsigned int,		nmi_count	)
+		__field(	unsigned int,		seqnum		)
+	),
+
+	F_printk("cnt:%u\tts:%010lu.%010lu\tinner:%llu\touter:%llunmi-ts:%llu\tnmi-count:%u\n",
+		 __entry->seqnum,
+		 __entry->tv_sec,
+		 __entry->tv_nsec,
+		 __entry->duration,
+		 __entry->outer_duration,
+		 __entry->nmi_total_ts,
+		 __entry->nmi_count),
+
+	FILTER_OTHER
+);

kernel/trace/trace_events_trigger.c

@@ -1028,6 +1028,7 @@ static struct event_command trigger_traceon_cmd = {
 static struct event_command trigger_traceoff_cmd = {
 	.name			= "traceoff",
 	.trigger_type		= ETT_TRACE_ONOFF,
+	.flags			= EVENT_CMD_FL_POST_TRIGGER,
 	.func			= event_trigger_callback,
 	.reg			= register_trigger,
 	.unreg			= unregister_trigger,

kernel/trace/trace_functions_graph.c

@@ -170,7 +170,6 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth,
 	current->ret_stack[index].ret = ret;
 	current->ret_stack[index].func = func;
 	current->ret_stack[index].calltime = calltime;
-	current->ret_stack[index].subtime = 0;
 #ifdef HAVE_FUNCTION_GRAPH_FP_TEST
 	current->ret_stack[index].fp = frame_pointer;
 #endif
@@ -1183,6 +1182,11 @@ print_graph_comment(struct trace_seq *s, struct trace_entry *ent,
 	trace_seq_puts(s, "/* ");
 
 	switch (iter->ent->type) {
+	case TRACE_BPUTS:
+		ret = trace_print_bputs_msg_only(iter);
+		if (ret != TRACE_TYPE_HANDLED)
+			return ret;
+		break;
 	case TRACE_BPRINT:
 		ret = trace_print_bprintk_msg_only(iter);
 		if (ret != TRACE_TYPE_HANDLED)

kernel/trace/trace_hwlat.c

@@ -0,0 +1,633 @@
+/*
+ * trace_hwlatdetect.c - A simple Hardware Latency detector.
+ *
+ * Use this tracer to detect large system latencies induced by the behavior of
+ * certain underlying system hardware or firmware, independent of Linux itself.
+ * The code was developed originally to detect the presence of SMIs on Intel
+ * and AMD systems, although there is no dependency upon x86 herein.
+ *
+ * The classical example usage of this tracer is in detecting the presence of
+ * SMIs or System Management Interrupts on Intel and AMD systems. An SMI is a
+ * somewhat special form of hardware interrupt spawned from earlier CPU debug
+ * modes in which the (BIOS/EFI/etc.) firmware arranges for the South Bridge
+ * LPC (or other device) to generate a special interrupt under certain
+ * circumstances, for example, upon expiration of a special SMI timer device,
+ * due to certain external thermal readings, on certain I/O address accesses,
+ * and other situations. An SMI hits a special CPU pin, triggers a special
+ * SMI mode (complete with special memory map), and the OS is unaware.
+ *
+ * Although certain hardware-inducing latencies are necessary (for example,
+ * a modern system often requires an SMI handler for correct thermal control
+ * and remote management) they can wreak havoc upon any OS-level performance
+ * guarantees toward low-latency, especially when the OS is not even made
+ * aware of the presence of these interrupts. For this reason, we need a
+ * somewhat brute force mechanism to detect these interrupts. In this case,
+ * we do it by hogging all of the CPU(s) for configurable timer intervals,
+ * sampling the built-in CPU timer, looking for discontiguous readings.
+ *
+ * WARNING: This implementation necessarily introduces latencies. Therefore,
+ *          you should NEVER use this tracer while running in a production
+ *          environment requiring any kind of low-latency performance
+ *          guarantee(s).
+ *
+ * Copyright (C) 2008-2009 Jon Masters, Red Hat, Inc. <jcm@redhat.com>
+ * Copyright (C) 2013-2016 Steven Rostedt, Red Hat, Inc. <srostedt@redhat.com>
+ *
+ * Includes useful feedback from Clark Williams <clark@redhat.com>
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ */
+#include <linux/kthread.h>
+#include <linux/tracefs.h>
+#include <linux/uaccess.h>
+#include <linux/cpumask.h>
+#include <linux/delay.h>
+#include "trace.h"
+
+static struct trace_array	*hwlat_trace;
+
+#define U64STR_SIZE		22			/* 20 digits max */
+
+#define BANNER			"hwlat_detector: "
+#define DEFAULT_SAMPLE_WINDOW	1000000			/* 1s */
+#define DEFAULT_SAMPLE_WIDTH	500000			/* 0.5s */
+#define DEFAULT_LAT_THRESHOLD	10			/* 10us */
+
+/* sampling thread*/
+static struct task_struct *hwlat_kthread;
+
+static struct dentry *hwlat_sample_width;	/* sample width us */
+static struct dentry *hwlat_sample_window;	/* sample window us */
+
+/* Save the previous tracing_thresh value */
+static unsigned long save_tracing_thresh;
+
+/* NMI timestamp counters */
+static u64 nmi_ts_start;
+static u64 nmi_total_ts;
+static int nmi_count;
+static int nmi_cpu;
+
+/* Tells NMIs to call back to the hwlat tracer to record timestamps */
+bool trace_hwlat_callback_enabled;
+
+/* If the user changed threshold, remember it */
+static u64 last_tracing_thresh = DEFAULT_LAT_THRESHOLD * NSEC_PER_USEC;
+
+/* Individual latency samples are stored here when detected. */
+struct hwlat_sample {
+	u64		seqnum;		/* unique sequence */
+	u64		duration;	/* delta */
+	u64		outer_duration;	/* delta (outer loop) */
+	u64		nmi_total_ts;	/* Total time spent in NMIs */
+	struct timespec	timestamp;	/* wall time */
+	int		nmi_count;	/* # NMIs during this sample */
+};
+
+/* keep the global state somewhere. */
+static struct hwlat_data {
+
+	struct mutex lock;		/* protect changes */
+
+	u64	count;			/* total since reset */
+
+	u64	sample_window;		/* total sampling window (on+off) */
+	u64	sample_width;		/* active sampling portion of window */
+
+} hwlat_data = {
+	.sample_window		= DEFAULT_SAMPLE_WINDOW,
+	.sample_width		= DEFAULT_SAMPLE_WIDTH,
+};
+
+static void trace_hwlat_sample(struct hwlat_sample *sample)
+{
+	struct trace_array *tr = hwlat_trace;
+	struct trace_event_call *call = &event_hwlat;
+	struct ring_buffer *buffer = tr->trace_buffer.buffer;
+	struct ring_buffer_event *event;
+	struct hwlat_entry *entry;
+	unsigned long flags;
+	int pc;
+
+	pc = preempt_count();
+	local_save_flags(flags);
+
+	event = trace_buffer_lock_reserve(buffer, TRACE_HWLAT, sizeof(*entry),
+					  flags, pc);
+	if (!event)
+		return;
+	entry	= ring_buffer_event_data(event);
+	entry->seqnum			= sample->seqnum;
+	entry->duration			= sample->duration;
+	entry->outer_duration		= sample->outer_duration;
+	entry->timestamp		= sample->timestamp;
+	entry->nmi_total_ts		= sample->nmi_total_ts;
+	entry->nmi_count		= sample->nmi_count;
+
+	if (!call_filter_check_discard(call, entry, buffer, event))
+		__buffer_unlock_commit(buffer, event);
+}
+
+/* Macros to encapsulate the time capturing infrastructure */
+#define time_type	u64
+#define time_get()	trace_clock_local()
+#define time_to_us(x)	div_u64(x, 1000)
+#define time_sub(a, b)	((a) - (b))
+#define init_time(a, b)	(a = b)
+#define time_u64(a)	a
+
+void trace_hwlat_callback(bool enter)
+{
+	if (smp_processor_id() != nmi_cpu)
+		return;
+
+	/*
+	 * Currently trace_clock_local() calls sched_clock() and the
+	 * generic version is not NMI safe.
+	 */
+	if (!IS_ENABLED(CONFIG_GENERIC_SCHED_CLOCK)) {
+		if (enter)
+			nmi_ts_start = time_get();
+		else
+			nmi_total_ts = time_get() - nmi_ts_start;
+	}
+
+	if (enter)
+		nmi_count++;
+}
+
+/**
+ * get_sample - sample the CPU TSC and look for likely hardware latencies
+ *
+ * Used to repeatedly capture the CPU TSC (or similar), looking for potential
+ * hardware-induced latency. Called with interrupts disabled and with
+ * hwlat_data.lock held.
+ */
+static int get_sample(void)
+{
+	struct trace_array *tr = hwlat_trace;
+	time_type start, t1, t2, last_t2;
+	s64 diff, total, last_total = 0;
+	u64 sample = 0;
+	u64 thresh = tracing_thresh;
+	u64 outer_sample = 0;
+	int ret = -1;
+
+	do_div(thresh, NSEC_PER_USEC); /* modifies interval value */
+
+	nmi_cpu = smp_processor_id();
+	nmi_total_ts = 0;
+	nmi_count = 0;
+	/* Make sure NMIs see this first */
+	barrier();
+
+	trace_hwlat_callback_enabled = true;
+
+	init_time(last_t2, 0);
+	start = time_get(); /* start timestamp */
+
+	do {
+
+		t1 = time_get();	/* we'll look for a discontinuity */
+		t2 = time_get();
+
+		if (time_u64(last_t2)) {
+			/* Check the delta from outer loop (t2 to next t1) */
+			diff = time_to_us(time_sub(t1, last_t2));
+			/* This shouldn't happen */
+			if (diff < 0) {
+				pr_err(BANNER "time running backwards\n");
+				goto out;
+			}
+			if (diff > outer_sample)
+				outer_sample = diff;
+		}
+		last_t2 = t2;
+
+		total = time_to_us(time_sub(t2, start)); /* sample width */
+
+		/* Check for possible overflows */
+		if (total < last_total) {
+			pr_err("Time total overflowed\n");
+			break;
+		}
+		last_total = total;
+
+		/* This checks the inner loop (t1 to t2) */
+		diff = time_to_us(time_sub(t2, t1));     /* current diff */
+
+		/* This shouldn't happen */
+		if (diff < 0) {
+			pr_err(BANNER "time running backwards\n");
+			goto out;
+		}
+
+		if (diff > sample)
+			sample = diff; /* only want highest value */
+
+	} while (total <= hwlat_data.sample_width);
+
+	barrier(); /* finish the above in the view for NMIs */
+	trace_hwlat_callback_enabled = false;
+	barrier(); /* Make sure nmi_total_ts is no longer updated */
+
+	ret = 0;
+
+	/* If we exceed the threshold value, we have found a hardware latency */
+	if (sample > thresh || outer_sample > thresh) {
+		struct hwlat_sample s;
+
+		ret = 1;
+
+		/* We read in microseconds */
+		if (nmi_total_ts)
+			do_div(nmi_total_ts, NSEC_PER_USEC);
+
+		hwlat_data.count++;
+		s.seqnum = hwlat_data.count;
+		s.duration = sample;
+		s.outer_duration = outer_sample;
+		s.timestamp = CURRENT_TIME;
+		s.nmi_total_ts = nmi_total_ts;
+		s.nmi_count = nmi_count;
+		trace_hwlat_sample(&s);
+
+		/* Keep a running maximum ever recorded hardware latency */
+		if (sample > tr->max_latency)
+			tr->max_latency = sample;
+	}
+
+out:
+	return ret;
+}
+
+static struct cpumask save_cpumask;
+static bool disable_migrate;
+
+static void move_to_next_cpu(void)
+{
+	static struct cpumask *current_mask;
+	int next_cpu;
+
+	if (disable_migrate)
+		return;
+
+	/* Just pick the first CPU on first iteration */
+	if (!current_mask) {
+		current_mask = &save_cpumask;
+		get_online_cpus();
+		cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask);
+		put_online_cpus();
+		next_cpu = cpumask_first(current_mask);
+		goto set_affinity;
+	}
+
+	/*
+	 * If for some reason the user modifies the CPU affinity
+	 * of this thread, than stop migrating for the duration
+	 * of the current test.
+	 */
+	if (!cpumask_equal(current_mask, &current->cpus_allowed))
+		goto disable;
+
+	get_online_cpus();
+	cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask);
+	next_cpu = cpumask_next(smp_processor_id(), current_mask);
+	put_online_cpus();
+
+	if (next_cpu >= nr_cpu_ids)
+		next_cpu = cpumask_first(current_mask);
+
+ set_affinity:
+	if (next_cpu >= nr_cpu_ids) /* Shouldn't happen! */
+		goto disable;
+
+	cpumask_clear(current_mask);
+	cpumask_set_cpu(next_cpu, current_mask);
+
+	sched_setaffinity(0, current_mask);
+	return;
+
+ disable:
+	disable_migrate = true;
+}
+
+/*
+ * kthread_fn - The CPU time sampling/hardware latency detection kernel thread
+ *
+ * Used to periodically sample the CPU TSC via a call to get_sample. We
+ * disable interrupts, which does (intentionally) introduce latency since we
+ * need to ensure nothing else might be running (and thus preempting).
+ * Obviously this should never be used in production environments.
+ *
+ * Currently this runs on which ever CPU it was scheduled on, but most
+ * real-world hardware latency situations occur across several CPUs,
+ * but we might later generalize this if we find there are any actualy
+ * systems with alternate SMI delivery or other hardware latencies.
+ */
+static int kthread_fn(void *data)
+{
+	u64 interval;
+
+	while (!kthread_should_stop()) {
+
+		move_to_next_cpu();
+
+		local_irq_disable();
+		get_sample();
+		local_irq_enable();
+
+		mutex_lock(&hwlat_data.lock);
+		interval = hwlat_data.sample_window - hwlat_data.sample_width;
+		mutex_unlock(&hwlat_data.lock);
+
+		do_div(interval, USEC_PER_MSEC); /* modifies interval value */
+
+		/* Always sleep for at least 1ms */
+		if (interval < 1)
+			interval = 1;
+
+		if (msleep_interruptible(interval))
+			break;
+	}
+
+	return 0;
+}
+
+/**
+ * start_kthread - Kick off the hardware latency sampling/detector kthread
+ *
+ * This starts the kernel thread that will sit and sample the CPU timestamp
+ * counter (TSC or similar) and look for potential hardware latencies.
+ */
+static int start_kthread(struct trace_array *tr)
+{
+	struct task_struct *kthread;
+
+	kthread = kthread_create(kthread_fn, NULL, "hwlatd");
+	if (IS_ERR(kthread)) {
+		pr_err(BANNER "could not start sampling thread\n");
+		return -ENOMEM;
+	}
+	hwlat_kthread = kthread;
+	wake_up_process(kthread);
+
+	return 0;
+}
+
+/**
+ * stop_kthread - Inform the hardware latency samping/detector kthread to stop
+ *
+ * This kicks the running hardware latency sampling/detector kernel thread and
+ * tells it to stop sampling now. Use this on unload and at system shutdown.
+ */
+static void stop_kthread(void)
+{
+	if (!hwlat_kthread)
+		return;
+	kthread_stop(hwlat_kthread);
+	hwlat_kthread = NULL;
+}
+
+/*
+ * hwlat_read - Wrapper read function for reading both window and width
+ * @filp: The active open file structure
+ * @ubuf: The userspace provided buffer to read value into
+ * @cnt: The maximum number of bytes to read
+ * @ppos: The current "file" position
+ *
+ * This function provides a generic read implementation for the global state
+ * "hwlat_data" structure filesystem entries.
+ */
+static ssize_t hwlat_read(struct file *filp, char __user *ubuf,
+			  size_t cnt, loff_t *ppos)
+{
+	char buf[U64STR_SIZE];
+	u64 *entry = filp->private_data;
+	u64 val;
+	int len;
+
+	if (!entry)
+		return -EFAULT;
+
+	if (cnt > sizeof(buf))
+		cnt = sizeof(buf);
+
+	val = *entry;
+
+	len = snprintf(buf, sizeof(buf), "%llu\n", val);
+
+	return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
+}
+
+/**
+ * hwlat_width_write - Write function for "width" entry
+ * @filp: The active open file structure
+ * @ubuf: The user buffer that contains the value to write
+ * @cnt: The maximum number of bytes to write to "file"
+ * @ppos: The current position in @file
+ *
+ * This function provides a write implementation for the "width" interface
+ * to the hardware latency detector. It can be used to configure
+ * for how many us of the total window us we will actively sample for any
+ * hardware-induced latency periods. Obviously, it is not possible to
+ * sample constantly and have the system respond to a sample reader, or,
+ * worse, without having the system appear to have gone out to lunch. It
+ * is enforced that width is less that the total window size.
+ */
+static ssize_t
+hwlat_width_write(struct file *filp, const char __user *ubuf,
+		  size_t cnt, loff_t *ppos)
+{
+	u64 val;
+	int err;
+
+	err = kstrtoull_from_user(ubuf, cnt, 10, &val);
+	if (err)
+		return err;
+
+	mutex_lock(&hwlat_data.lock);
+	if (val < hwlat_data.sample_window)
+		hwlat_data.sample_width = val;
+	else
+		err = -EINVAL;
+	mutex_unlock(&hwlat_data.lock);
+
+	if (err)
+		return err;
+
+	return cnt;
+}
+
+/**
+ * hwlat_window_write - Write function for "window" entry
+ * @filp: The active open file structure
+ * @ubuf: The user buffer that contains the value to write
+ * @cnt: The maximum number of bytes to write to "file"
+ * @ppos: The current position in @file
+ *
+ * This function provides a write implementation for the "window" interface
+ * to the hardware latency detetector. The window is the total time
+ * in us that will be considered one sample period. Conceptually, windows
+ * occur back-to-back and contain a sample width period during which
+ * actual sampling occurs. Can be used to write a new total window size. It
+ * is enfoced that any value written must be greater than the sample width
+ * size, or an error results.
+ */
+static ssize_t
+hwlat_window_write(struct file *filp, const char __user *ubuf,
+		   size_t cnt, loff_t *ppos)
+{
+	u64 val;
+	int err;
+
+	err = kstrtoull_from_user(ubuf, cnt, 10, &val);
+	if (err)
+		return err;
+
+	mutex_lock(&hwlat_data.lock);
+	if (hwlat_data.sample_width < val)
+		hwlat_data.sample_window = val;
+	else
+		err = -EINVAL;
+	mutex_unlock(&hwlat_data.lock);
+
+	if (err)
+		return err;
+
+	return cnt;
+}
+
+static const struct file_operations width_fops = {
+	.open		= tracing_open_generic,
+	.read		= hwlat_read,
+	.write		= hwlat_width_write,
+};
+
+static const struct file_operations window_fops = {
+	.open		= tracing_open_generic,
+	.read		= hwlat_read,
+	.write		= hwlat_window_write,
+};
+
+/**
+ * init_tracefs - A function to initialize the tracefs interface files
+ *
+ * This function creates entries in tracefs for "hwlat_detector".
+ * It creates the hwlat_detector directory in the tracing directory,
+ * and within that directory is the count, width and window files to
+ * change and view those values.
+ */
+static int init_tracefs(void)
+{
+	struct dentry *d_tracer;
+	struct dentry *top_dir;
+
+	d_tracer = tracing_init_dentry();
+	if (IS_ERR(d_tracer))
+		return -ENOMEM;
+
+	top_dir = tracefs_create_dir("hwlat_detector", d_tracer);
+	if (!top_dir)
+		return -ENOMEM;
+
+	hwlat_sample_window = tracefs_create_file("window", 0640,
+						  top_dir,
+						  &hwlat_data.sample_window,
+						  &window_fops);
+	if (!hwlat_sample_window)
+		goto err;
+
+	hwlat_sample_width = tracefs_create_file("width", 0644,
+						 top_dir,
+						 &hwlat_data.sample_width,
+						 &width_fops);
+	if (!hwlat_sample_width)
+		goto err;
+
+	return 0;
+
+ err:
+	tracefs_remove_recursive(top_dir);
+	return -ENOMEM;
+}
+
+static void hwlat_tracer_start(struct trace_array *tr)
+{
+	int err;
+
+	err = start_kthread(tr);
+	if (err)
+		pr_err(BANNER "Cannot start hwlat kthread\n");
+}
+
+static void hwlat_tracer_stop(struct trace_array *tr)
+{
+	stop_kthread();
+}
+
+static bool hwlat_busy;
+
+static int hwlat_tracer_init(struct trace_array *tr)
+{
+	/* Only allow one instance to enable this */
+	if (hwlat_busy)
+		return -EBUSY;
+
+	hwlat_trace = tr;
+
+	disable_migrate = false;
+	hwlat_data.count = 0;
+	tr->max_latency = 0;
+	save_tracing_thresh = tracing_thresh;
+
+	/* tracing_thresh is in nsecs, we speak in usecs */
+	if (!tracing_thresh)
+		tracing_thresh = last_tracing_thresh;
+
+	if (tracer_tracing_is_on(tr))
+		hwlat_tracer_start(tr);
+
+	hwlat_busy = true;
+
+	return 0;
+}
+
+static void hwlat_tracer_reset(struct trace_array *tr)
+{
+	stop_kthread();
+
+	/* the tracing threshold is static between runs */
+	last_tracing_thresh = tracing_thresh;
+
+	tracing_thresh = save_tracing_thresh;
+	hwlat_busy = false;
+}
+
+static struct tracer hwlat_tracer __read_mostly =
+{
+	.name		= "hwlat",
+	.init		= hwlat_tracer_init,
+	.reset		= hwlat_tracer_reset,
+	.start		= hwlat_tracer_start,
+	.stop		= hwlat_tracer_stop,
+	.allow_instances = true,
+};
+
+__init static int init_hwlat_tracer(void)
+{
+	int ret;
+
+	mutex_init(&hwlat_data.lock);
+
+	ret = register_tracer(&hwlat_tracer);
+	if (ret)
+		return ret;
+
+	init_tracefs();
+
+	return 0;
+}
+late_initcall(init_hwlat_tracer);

kernel/trace/trace_output.c

@@ -1098,6 +1098,71 @@ static struct trace_event trace_user_stack_event = {
 	.funcs		= &trace_user_stack_funcs,
 };
 
+/* TRACE_HWLAT */
+static enum print_line_t
+trace_hwlat_print(struct trace_iterator *iter, int flags,
+		  struct trace_event *event)
+{
+	struct trace_entry *entry = iter->ent;
+	struct trace_seq *s = &iter->seq;
+	struct hwlat_entry *field;
+
+	trace_assign_type(field, entry);
+
+	trace_seq_printf(s, "#%-5u inner/outer(us): %4llu/%-5llu ts:%ld.%09ld",
+			 field->seqnum,
+			 field->duration,
+			 field->outer_duration,
+			 field->timestamp.tv_sec,
+			 field->timestamp.tv_nsec);
+
+	if (field->nmi_count) {
+		/*
+		 * The generic sched_clock() is not NMI safe, thus
+		 * we only record the count and not the time.
+		 */
+		if (!IS_ENABLED(CONFIG_GENERIC_SCHED_CLOCK))
+			trace_seq_printf(s, " nmi-total:%llu",
+					 field->nmi_total_ts);
+		trace_seq_printf(s, " nmi-count:%u",
+				 field->nmi_count);
+	}
+
+	trace_seq_putc(s, '\n');
+
+	return trace_handle_return(s);
+}
+
+
+static enum print_line_t
+trace_hwlat_raw(struct trace_iterator *iter, int flags,
+		struct trace_event *event)
+{
+	struct hwlat_entry *field;
+	struct trace_seq *s = &iter->seq;
+
+	trace_assign_type(field, iter->ent);
+
+	trace_seq_printf(s, "%llu %lld %ld %09ld %u\n",
+			 field->duration,
+			 field->outer_duration,
+			 field->timestamp.tv_sec,
+			 field->timestamp.tv_nsec,
+			 field->seqnum);
+
+	return trace_handle_return(s);
+}
+
+static struct trace_event_functions trace_hwlat_funcs = {
+	.trace		= trace_hwlat_print,
+	.raw		= trace_hwlat_raw,
+};
+
+static struct trace_event trace_hwlat_event = {
+	.type		= TRACE_HWLAT,
+	.funcs		= &trace_hwlat_funcs,
+};
+
 /* TRACE_BPUTS */
 static enum print_line_t
 trace_bputs_print(struct trace_iterator *iter, int flags,
@@ -1233,6 +1298,7 @@ static struct trace_event *events[] __initdata = {
 	&trace_bputs_event,
 	&trace_bprint_event,
 	&trace_print_event,
+	&trace_hwlat_event,
 	NULL
 };
 

kernel/trace/trace_uprobe.c

@@ -431,10 +431,6 @@ static int create_trace_uprobe(int argc, char **argv)
 		pr_info("Probe point is not specified.\n");
 		return -EINVAL;
 	}
-	if (isdigit(argv[1][0])) {
-		pr_info("probe point must be have a filename.\n");
-		return -EINVAL;
-	}
 	arg = strchr(argv[1], ':');
 	if (!arg) {
 		ret = -EINVAL;

scripts/tracing/ftrace-bisect.sh

@@ -0,0 +1,115 @@
+#!/bin/bash
+#
+# Here's how to use this:
+#
+# This script is used to help find functions that are being traced by function
+# tracer or function graph tracing that causes the machine to reboot, hang, or
+# crash. Here's the steps to take.
+#
+# First, determine if function tracing is working with a single function:
+#
+#   (note, if this is a problem with function_graph tracing, then simply
+#    replace "function" with "function_graph" in the following steps).
+#
+#  # cd /sys/kernel/debug/tracing
+#  # echo schedule > set_ftrace_filter
+#  # echo function > current_tracer
+#
+# If this works, then we know that something is being traced that shouldn't be.
+#
+#  # echo nop > current_tracer
+#
+#  # cat available_filter_functions > ~/full-file
+#  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
+#  # cat ~/test-file > set_ftrace_filter
+#
+# *** Note *** this will take several minutes. Setting multiple functions is
+# an O(n^2) operation, and we are dealing with thousands of functions. So go
+# have  coffee, talk with your coworkers, read facebook. And eventually, this
+# operation will end.
+#
+#  # echo function > current_tracer
+#
+# If it crashes, we know that ~/test-file has a bad function.
+#
+#   Reboot back to test kernel.
+#
+#     # cd /sys/kernel/debug/tracing
+#     # mv ~/test-file ~/full-file
+#
+# If it didn't crash.
+#
+#     # echo nop > current_tracer
+#     # mv ~/non-test-file ~/full-file
+#
+# Get rid of the other test file from previous run (or save them off somewhere).
+#  # rm -f ~/test-file ~/non-test-file
+#
+# And start again:
+#
+#  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
+#
+# The good thing is, because this cuts the number of functions in ~/test-file
+# by half, the cat of it into set_ftrace_filter takes half as long each
+# iteration, so don't talk so much at the water cooler the second time.
+#
+# Eventually, if you did this correctly, you will get down to the problem
+# function, and all we need to do is to notrace it.
+#
+# The way to figure out if the problem function is bad, just do:
+#
+#  # echo <problem-function> > set_ftrace_notrace
+#  # echo > set_ftrace_filter
+#  # echo function > current_tracer
+#
+# And if it doesn't crash, we are done.
+#
+# If it does crash, do this again (there's more than one problem function)
+# but you need to echo the problem function(s) into set_ftrace_notrace before
+# enabling function tracing in the above steps. Or if you can compile the
+# kernel, annotate the problem functions with "notrace" and start again.
+#
+
+
+if [ $# -ne 3 ]; then
+  echo 'usage: ftrace-bisect full-file test-file  non-test-file'
+  exit
+fi
+
+full=$1
+test=$2
+nontest=$3
+
+x=`cat $full | wc -l`
+if [ $x -eq 1 ]; then
+	echo "There's only one function left, must be the bad one"
+	cat $full
+	exit 0
+fi
+
+let x=$x/2
+let y=$x+1
+
+if [ ! -f $full ]; then
+	echo "$full does not exist"
+	exit 1
+fi
+
+if [ -f $test ]; then
+	echo -n "$test exists, delete it? [y/N]"
+	read a
+	if [ "$a" != "y" -a "$a" != "Y" ]; then
+		exit 1
+	fi
+fi
+
+if [ -f $nontest ]; then
+	echo -n "$nontest exists, delete it? [y/N]"
+	read a
+	if [ "$a" != "y" -a "$a" != "Y" ]; then
+		exit 1
+	fi
+fi
+
+sed -ne "1,${x}p" $full > $test
+sed -ne "$y,\$p" $full > $nontest