tracing: Add trace_puts() for even faster trace_printk() tracing

The trace_printk() is extremely fast and is very handy as it can be
used in any context (including NMIs!). But it still requires scanning
the fmt string for parsing the args. Even the trace_bprintk() requires
a scan to know what args will be saved, although it doesn't copy the
format string itself.

Several times trace_printk() has no args, and wastes cpu cycles scanning
the fmt string.

Adding trace_puts() allows the developer to use an even faster
tracing method that only saves the pointer to the string in the
ring buffer without doing any format parsing at all. This will
help remove even more of the "Heisenbug" effect, when debugging.

Also fixed up the F_printk()s for the ftrace internal bprint and print events.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

5 files changed, 174 insertions, 4 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4021a5e..5043a0c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -350,6 +350,77 @@ void tracing_on(void)
 }
 EXPORT_SYMBOL_GPL(tracing_on);
 
+/**
+ * __trace_puts - write a constant string into the trace buffer.
+ * @ip:	   The address of the caller
+ * @str:   The constant string to write
+ * @size:  The size of the string.
+ */
+int __trace_puts(unsigned long ip, const char *str, int size)
+{
+	struct ring_buffer_event *event;
+	struct ring_buffer *buffer;
+	struct print_entry *entry;
+	unsigned long irq_flags;
+	int alloc;
+
+	alloc = sizeof(*entry) + size + 2; /* possible \n added */
+
+	local_save_flags(irq_flags);
+	buffer = global_trace.trace_buffer.buffer;
+	event = trace_buffer_lock_reserve(buffer, TRACE_PRINT, alloc, 
+					  irq_flags, preempt_count());
+	if (!event)
+		return 0;
+
+	entry = ring_buffer_event_data(event);
+	entry->ip = ip;
+
+	memcpy(&entry->buf, str, size);
+
+	/* Add a newline if necessary */
+	if (entry->buf[size - 1] != '\n') {
+		entry->buf[size] = '\n';
+		entry->buf[size + 1] = '\0';
+	} else
+		entry->buf[size] = '\0';
+
+	__buffer_unlock_commit(buffer, event);
+
+	return size;
+}
+EXPORT_SYMBOL_GPL(__trace_puts);
+
+/**
+ * __trace_bputs - write the pointer to a constant string into trace buffer
+ * @ip:	   The address of the caller
+ * @str:   The constant string to write to the buffer to
+ */
+int __trace_bputs(unsigned long ip, const char *str)
+{
+	struct ring_buffer_event *event;
+	struct ring_buffer *buffer;
+	struct bputs_entry *entry;
+	unsigned long irq_flags;
+	int size = sizeof(struct bputs_entry);
+
+	local_save_flags(irq_flags);
+	buffer = global_trace.trace_buffer.buffer;
+	event = trace_buffer_lock_reserve(buffer, TRACE_BPUTS, size,
+					  irq_flags, preempt_count());
+	if (!event)
+		return 0;
+
+	entry = ring_buffer_event_data(event);
+	entry->ip			= ip;
+	entry->str			= str;
+
+	__buffer_unlock_commit(buffer, event);
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(__trace_bputs);
+
 #ifdef CONFIG_TRACER_SNAPSHOT
 /**
  * trace_snapshot - take a snapshot of the current buffer.
@@ -2475,6 +2546,11 @@ enum print_line_t print_trace_line(struct trace_iterator *iter)
 			return ret;
 	}
 
+	if (iter->ent->type == TRACE_BPUTS &&
+			trace_flags & TRACE_ITER_PRINTK &&
+			trace_flags & TRACE_ITER_PRINTK_MSGONLY)
+		return trace_print_bputs_msg_only(iter);
+
 	if (iter->ent->type == TRACE_BPRINT &&
 			trace_flags & TRACE_ITER_PRINTK &&
 			trace_flags & TRACE_ITER_PRINTK_MSGONLY)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 26bc718..d5764a8 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -34,6 +34,7 @@ enum trace_type {
 	TRACE_GRAPH_ENT,
 	TRACE_USER_STACK,
 	TRACE_BLK,
+	TRACE_BPUTS,
 
 	__TRACE_LAST_TYPE,
 };
@@ -277,6 +278,7 @@ extern void __ftrace_bad_type(void);
 		IF_ASSIGN(var, ent, struct userstack_entry, TRACE_USER_STACK);\
 		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 trace_mmiotrace_rw,		\
 			  TRACE_MMIO_RW);				\
 		IF_ASSIGN(var, ent, struct trace_mmiotrace_map,		\
diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index 4108e12..e2d027a 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -223,8 +223,8 @@ FTRACE_ENTRY(bprint, bprint_entry,
 		__dynamic_array(	u32,	buf	)
 	),
 
-	F_printk("%08lx fmt:%p",
-		 __entry->ip, __entry->fmt),
+	F_printk("%pf: %s",
+		 (void *)__entry->ip, __entry->fmt),
 
 	FILTER_OTHER
 );
@@ -238,8 +238,23 @@ FTRACE_ENTRY(print, print_entry,
 		__dynamic_array(	char,	buf	)
 	),
 
-	F_printk("%08lx %s",
-		 __entry->ip, __entry->buf),
+	F_printk("%pf: %s",
+		 (void *)__entry->ip, __entry->buf),
+
+	FILTER_OTHER
+);
+
+FTRACE_ENTRY(bputs, bputs_entry,
+
+	TRACE_BPUTS,
+
+	F_STRUCT(
+		__field(	unsigned long,	ip	)
+		__field(	const char *,	str	)
+	),
+
+	F_printk("%pf: %s",
+		 (void *)__entry->ip, __entry->str),
 
 	FILTER_OTHER
 );
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 2edc722..19f48e7 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -37,6 +37,22 @@ int trace_print_seq(struct seq_file *m, struct trace_seq *s)
 	return ret;
 }
 
+enum print_line_t trace_print_bputs_msg_only(struct trace_iterator *iter)
+{
+	struct trace_seq *s = &iter->seq;
+	struct trace_entry *entry = iter->ent;
+	struct bputs_entry *field;
+	int ret;
+
+	trace_assign_type(field, entry);
+
+	ret = trace_seq_puts(s, field->str);
+	if (!ret)
+		return TRACE_TYPE_PARTIAL_LINE;
+
+	return TRACE_TYPE_HANDLED;
+}
+
 enum print_line_t trace_print_bprintk_msg_only(struct trace_iterator *iter)
 {
 	struct trace_seq *s = &iter->seq;
@@ -1244,6 +1260,64 @@ static struct trace_event trace_user_stack_event = {
 	.funcs		= &trace_user_stack_funcs,
 };
 
+/* TRACE_BPUTS */
+static enum print_line_t
+trace_bputs_print(struct trace_iterator *iter, int flags,
+		   struct trace_event *event)
+{
+	struct trace_entry *entry = iter->ent;
+	struct trace_seq *s = &iter->seq;
+	struct bputs_entry *field;
+
+	trace_assign_type(field, entry);
+
+	if (!seq_print_ip_sym(s, field->ip, flags))
+		goto partial;
+
+	if (!trace_seq_puts(s, ": "))
+		goto partial;
+
+	if (!trace_seq_puts(s, field->str))
+		goto partial;
+
+	return TRACE_TYPE_HANDLED;
+
+ partial:
+	return TRACE_TYPE_PARTIAL_LINE;
+}
+
+
+static enum print_line_t
+trace_bputs_raw(struct trace_iterator *iter, int flags,
+		struct trace_event *event)
+{
+	struct bputs_entry *field;
+	struct trace_seq *s = &iter->seq;
+
+	trace_assign_type(field, iter->ent);
+
+	if (!trace_seq_printf(s, ": %lx : ", field->ip))
+		goto partial;
+
+	if (!trace_seq_puts(s, field->str))
+		goto partial;
+
+	return TRACE_TYPE_HANDLED;
+
+ partial:
+	return TRACE_TYPE_PARTIAL_LINE;
+}
+
+static struct trace_event_functions trace_bputs_funcs = {
+	.trace		= trace_bputs_print,
+	.raw		= trace_bputs_raw,
+};
+
+static struct trace_event trace_bputs_event = {
+	.type		= TRACE_BPUTS,
+	.funcs		= &trace_bputs_funcs,
+};
+
 /* TRACE_BPRINT */
 static enum print_line_t
 trace_bprint_print(struct trace_iterator *iter, int flags,
@@ -1356,6 +1430,7 @@ static struct trace_event *events[] __initdata = {
 	&trace_wake_event,
 	&trace_stack_event,
 	&trace_user_stack_event,
+	&trace_bputs_event,
 	&trace_bprint_event,
 	&trace_print_event,
 	NULL
diff --git a/kernel/trace/trace_output.h b/kernel/trace/trace_output.h
index c038eba..af77870 100644
--- a/kernel/trace/trace_output.h
+++ b/kernel/trace/trace_output.h
@@ -5,6 +5,8 @@
 #include "trace.h"
 
 extern enum print_line_t
+trace_print_bputs_msg_only(struct trace_iterator *iter);
+extern enum print_line_t
 trace_print_bprintk_msg_only(struct trace_iterator *iter);
 extern enum print_line_t
 trace_print_printk_msg_only(struct trace_iterator *iter);