tracing: pass around ring buffer instead of tracer

The latency tracers (irqsoff and wakeup) can swap trace buffers
on the fly. If an event is happening and has reserved data on one of
the buffers, and the latency tracer swaps the global buffer with the
max buffer, the result is that the event may commit the data to the
wrong buffer.

This patch changes the API to the trace recording to be recieve the
buffer that was used to reserve a commit. Then this buffer can be passed
in to the commit.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/linux/ftrace_event.h

@@ -93,13 +93,17 @@ void tracing_generic_entry_update(struct trace_entry *entry,
 				  unsigned long flags,
 				  int pc);
 struct ring_buffer_event *
-trace_current_buffer_lock_reserve(int type, unsigned long len,
+trace_current_buffer_lock_reserve(struct ring_buffer **current_buffer,
+				  int type, unsigned long len,
 				  unsigned long flags, int pc);
-void trace_current_buffer_unlock_commit(struct ring_buffer_event *event,
+void trace_current_buffer_unlock_commit(struct ring_buffer *buffer,
+					struct ring_buffer_event *event,
 					unsigned long flags, int pc);
-void trace_nowake_buffer_unlock_commit(struct ring_buffer_event *event,
+void trace_nowake_buffer_unlock_commit(struct ring_buffer *buffer,
+				       struct ring_buffer_event *event,
 					unsigned long flags, int pc);
-void trace_current_buffer_discard_commit(struct ring_buffer_event *event);
+void trace_current_buffer_discard_commit(struct ring_buffer *buffer,
+					 struct ring_buffer_event *event);
 
 void tracing_record_cmdline(struct task_struct *tsk);
 
@@ -135,7 +139,8 @@ struct ftrace_event_call {
 
 extern void destroy_preds(struct ftrace_event_call *call);
 extern int filter_match_preds(struct ftrace_event_call *call, void *rec);
-extern int filter_current_check_discard(struct ftrace_event_call *call,
+extern int filter_current_check_discard(struct ring_buffer *buffer,
+					struct ftrace_event_call *call,
 					void *rec,
 					struct ring_buffer_event *event);
 

include/trace/ftrace.h

@@ -460,13 +460,15 @@ static void ftrace_profile_disable_##call(struct ftrace_event_call *event_call)\
  * {
  *	struct ring_buffer_event *event;
  *	struct ftrace_raw_<call> *entry; <-- defined in stage 1
+ *	struct ring_buffer *buffer;
  *	unsigned long irq_flags;
  *	int pc;
  *
  *	local_save_flags(irq_flags);
  *	pc = preempt_count();
  *
- *	event = trace_current_buffer_lock_reserve(event_<call>.id,
+ *	event = trace_current_buffer_lock_reserve(&buffer,
+ *				  event_<call>.id,
  *				  sizeof(struct ftrace_raw_<call>),
  *				  irq_flags, pc);
  *	if (!event)
@@ -476,7 +478,7 @@ static void ftrace_profile_disable_##call(struct ftrace_event_call *event_call)\
  *	<assign>;  <-- Here we assign the entries by the __field and
  *			__array macros.
  *
- *	trace_current_buffer_unlock_commit(event, irq_flags, pc);
+ *	trace_current_buffer_unlock_commit(buffer, event, irq_flags, pc);
  * }
  *
  * static int ftrace_raw_reg_event_<call>(void)
@@ -568,6 +570,7 @@ static void ftrace_raw_event_##call(proto)				\
 	struct ftrace_event_call *event_call = &event_##call;		\
 	struct ring_buffer_event *event;				\
 	struct ftrace_raw_##call *entry;				\
+	struct ring_buffer *buffer;					\
 	unsigned long irq_flags;					\
 	int __data_size;						\
 	int pc;								\
@@ -577,7 +580,8 @@ static void ftrace_raw_event_##call(proto)				\
 									\
 	__data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
 									\
-	event = trace_current_buffer_lock_reserve(event_##call.id,	\
+	event = trace_current_buffer_lock_reserve(&buffer,		\
+				 event_##call.id,			\
 				 sizeof(*entry) + __data_size,		\
 				 irq_flags, pc);			\
 	if (!event)							\
@@ -589,8 +593,9 @@ static void ftrace_raw_event_##call(proto)				\
 									\
 	{ assign; }							\
 									\
-	if (!filter_current_check_discard(event_call, entry, event))	\
-		trace_nowake_buffer_unlock_commit(event, irq_flags, pc); \
+	if (!filter_current_check_discard(buffer, event_call, entry, event)) \
+		trace_nowake_buffer_unlock_commit(buffer,		\
+						  event, irq_flags, pc); \
 }									\
 									\
 static int ftrace_raw_reg_event_##call(void *ptr)			\

kernel/trace/blktrace.c

@@ -65,13 +65,15 @@ static void trace_note(struct blk_trace *bt, pid_t pid, int action,
 {
 	struct blk_io_trace *t;
 	struct ring_buffer_event *event = NULL;
+	struct ring_buffer *buffer = NULL;
 	int pc = 0;
 	int cpu = smp_processor_id();
 	bool blk_tracer = blk_tracer_enabled;
 
 	if (blk_tracer) {
+		buffer = blk_tr->buffer;
 		pc = preempt_count();
-		event = trace_buffer_lock_reserve(blk_tr, TRACE_BLK,
+		event = trace_buffer_lock_reserve(buffer, TRACE_BLK,
 						  sizeof(*t) + len,
 						  0, pc);
 		if (!event)
@@ -96,7 +98,7 @@ static void trace_note(struct blk_trace *bt, pid_t pid, int action,
 		memcpy((void *) t + sizeof(*t), data, len);
 
 		if (blk_tracer)
-			trace_buffer_unlock_commit(blk_tr, event, 0, pc);
+			trace_buffer_unlock_commit(buffer, event, 0, pc);
 	}
 }
 
@@ -179,6 +181,7 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 {
 	struct task_struct *tsk = current;
 	struct ring_buffer_event *event = NULL;
+	struct ring_buffer *buffer = NULL;
 	struct blk_io_trace *t;
 	unsigned long flags = 0;
 	unsigned long *sequence;
@@ -204,8 +207,9 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 	if (blk_tracer) {
 		tracing_record_cmdline(current);
 
+		buffer = blk_tr->buffer;
 		pc = preempt_count();
-		event = trace_buffer_lock_reserve(blk_tr, TRACE_BLK,
+		event = trace_buffer_lock_reserve(buffer, TRACE_BLK,
 						  sizeof(*t) + pdu_len,
 						  0, pc);
 		if (!event)
@@ -252,7 +256,7 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 			memcpy((void *) t + sizeof(*t), pdu_data, pdu_len);
 
 		if (blk_tracer) {
-			trace_buffer_unlock_commit(blk_tr, event, 0, pc);
+			trace_buffer_unlock_commit(buffer, event, 0, pc);
 			return;
 		}
 	}