tracing: Add support for recording tgid of tasks

Inorder to support recording of tgid, the following changes are made:

* Introduce a new API (tracing_record_taskinfo) to additionally record the tgid
  along with the task's comm at the same time. This has has the benefit of not
  setting trace_cmdline_save before all the information for a task is saved.
* Add a new API tracing_record_taskinfo_sched_switch to record task information
  for 2 tasks at a time (previous and next) and use it from sched_switch probe.
* Preserve the old API (tracing_record_cmdline) and create it as a wrapper
  around the new one so that existing callers aren't affected.
* Reuse the existing sched_switch and sched_wakeup probes to record tgid
  information and add a new option 'record-tgid' to enable recording of tgid

When record-tgid option isn't enabled to being with, we take care to make sure
that there's isn't memory or runtime overhead.

Link: http://lkml.kernel.org/r/20170627020155.5139-1-joelaf@google.com

Cc: kernel-team@android.com
Cc: Ingo Molnar <mingo@redhat.com>
Tested-by: Michael Sartain <mikesart@gmail.com>
Signed-off-by: Joel Fernandes <joelaf@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

include/linux/trace_events.h

@@ -151,7 +151,15 @@ trace_event_buffer_lock_reserve(struct ring_buffer **current_buffer,
 				int type, unsigned long len,
 				unsigned long flags, int pc);
 
-void tracing_record_cmdline(struct task_struct *tsk);
+#define TRACE_RECORD_CMDLINE	BIT(0)
+#define TRACE_RECORD_TGID	BIT(1)
+
+void tracing_record_taskinfo(struct task_struct *task, int flags);
+void tracing_record_taskinfo_sched_switch(struct task_struct *prev,
+					  struct task_struct *next, int flags);
+
+void tracing_record_cmdline(struct task_struct *task);
+void tracing_record_tgid(struct task_struct *task);
 
 int trace_output_call(struct trace_iterator *iter, char *name, char *fmt, ...);
 
@@ -290,6 +298,7 @@ struct trace_subsystem_dir;
 enum {
 	EVENT_FILE_FL_ENABLED_BIT,
 	EVENT_FILE_FL_RECORDED_CMD_BIT,
+	EVENT_FILE_FL_RECORDED_TGID_BIT,
 	EVENT_FILE_FL_FILTERED_BIT,
 	EVENT_FILE_FL_NO_SET_FILTER_BIT,
 	EVENT_FILE_FL_SOFT_MODE_BIT,
@@ -303,6 +312,7 @@ enum {
  * Event file flags:
  *  ENABLED	  - The event is enabled
  *  RECORDED_CMD  - The comms should be recorded at sched_switch
+ *  RECORDED_TGID - The tgids should be recorded at sched_switch
  *  FILTERED	  - The event has a filter attached
  *  NO_SET_FILTER - Set when filter has error and is to be ignored
  *  SOFT_MODE     - The event is enabled/disabled by SOFT_DISABLED
@@ -315,6 +325,7 @@ enum {
 enum {
 	EVENT_FILE_FL_ENABLED		= (1 << EVENT_FILE_FL_ENABLED_BIT),
 	EVENT_FILE_FL_RECORDED_CMD	= (1 << EVENT_FILE_FL_RECORDED_CMD_BIT),
+	EVENT_FILE_FL_RECORDED_TGID	= (1 << EVENT_FILE_FL_RECORDED_TGID_BIT),
 	EVENT_FILE_FL_FILTERED		= (1 << EVENT_FILE_FL_FILTERED_BIT),
 	EVENT_FILE_FL_NO_SET_FILTER	= (1 << EVENT_FILE_FL_NO_SET_FILTER_BIT),
 	EVENT_FILE_FL_SOFT_MODE		= (1 << EVENT_FILE_FL_SOFT_MODE_BIT),

kernel/trace/trace.c

@@ -87,7 +87,7 @@ dummy_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
  * tracing is active, only save the comm when a trace event
  * occurred.
  */
-static DEFINE_PER_CPU(bool, trace_cmdline_save);
+static DEFINE_PER_CPU(bool, trace_taskinfo_save);
 
 /*
  * Kill all tracing for good (never come back).
@@ -790,7 +790,7 @@ EXPORT_SYMBOL_GPL(tracing_on);
 static __always_inline void
 __buffer_unlock_commit(struct ring_buffer *buffer, struct ring_buffer_event *event)
 {
-	__this_cpu_write(trace_cmdline_save, true);
+	__this_cpu_write(trace_taskinfo_save, true);
 
 	/* If this is the temp buffer, we need to commit fully */
 	if (this_cpu_read(trace_buffered_event) == event) {
@@ -1709,6 +1709,8 @@ void tracing_reset_all_online_cpus(void)
 	}
 }
 
+static int *tgid_map;
+
 #define SAVED_CMDLINES_DEFAULT 128
 #define NO_CMDLINE_MAP UINT_MAX
 static arch_spinlock_t trace_cmdline_lock = __ARCH_SPIN_LOCK_UNLOCKED;
@@ -1722,7 +1724,7 @@ struct saved_cmdlines_buffer {
 static struct saved_cmdlines_buffer *savedcmd;
 
 /* temporary disable recording */
-static atomic_t trace_record_cmdline_disabled __read_mostly;
+static atomic_t trace_record_taskinfo_disabled __read_mostly;
 
 static inline char *get_saved_cmdlines(int idx)
 {
@@ -1990,16 +1992,87 @@ void trace_find_cmdline(int pid, char comm[])
 	preempt_enable();
 }
 
-void tracing_record_cmdline(struct task_struct *tsk)
+int trace_find_tgid(int pid)
+{
+	if (unlikely(!tgid_map || !pid || pid > PID_MAX_DEFAULT))
+		return 0;
+
+	return tgid_map[pid];
+}
+
+static int trace_save_tgid(struct task_struct *tsk)
 {
-	if (atomic_read(&trace_record_cmdline_disabled) || !tracing_is_on())
+	if (unlikely(!tgid_map || !tsk->pid || tsk->pid > PID_MAX_DEFAULT))
+		return 0;
+
+	tgid_map[tsk->pid] = tsk->tgid;
+	return 1;
+}
+
+static bool tracing_record_taskinfo_skip(int flags)
+{
+	if (unlikely(!(flags & (TRACE_RECORD_CMDLINE | TRACE_RECORD_TGID))))
+		return true;
+	if (atomic_read(&trace_record_taskinfo_disabled) || !tracing_is_on())
+		return true;
+	if (!__this_cpu_read(trace_taskinfo_save))
+		return true;
+	return false;
+}
+
+/**
+ * tracing_record_taskinfo - record the task info of a task
+ *
+ * @task  - task to record
+ * @flags - TRACE_RECORD_CMDLINE for recording comm
+ *        - TRACE_RECORD_TGID for recording tgid
+ */
+void tracing_record_taskinfo(struct task_struct *task, int flags)
+{
+	if (tracing_record_taskinfo_skip(flags))
+		return;
+	if ((flags & TRACE_RECORD_CMDLINE) && !trace_save_cmdline(task))
+		return;
+	if ((flags & TRACE_RECORD_TGID) && !trace_save_tgid(task))
 		return;
 
-	if (!__this_cpu_read(trace_cmdline_save))
+	__this_cpu_write(trace_taskinfo_save, false);
+}
+
+/**
+ * tracing_record_taskinfo_sched_switch - record task info for sched_switch
+ *
+ * @prev - previous task during sched_switch
+ * @next - next task during sched_switch
+ * @flags - TRACE_RECORD_CMDLINE for recording comm
+ *          TRACE_RECORD_TGID for recording tgid
+ */
+void tracing_record_taskinfo_sched_switch(struct task_struct *prev,
+					  struct task_struct *next, int flags)
+{
+	if (tracing_record_taskinfo_skip(flags))
 		return;
 
-	if (trace_save_cmdline(tsk))
-		__this_cpu_write(trace_cmdline_save, false);
+	if ((flags & TRACE_RECORD_CMDLINE) &&
+	    (!trace_save_cmdline(prev) || !trace_save_cmdline(next)))
+		return;
+
+	if ((flags & TRACE_RECORD_TGID) &&
+	    (!trace_save_tgid(prev) || !trace_save_tgid(next)))
+		return;
+
+	__this_cpu_write(trace_taskinfo_save, false);
+}
+
+/* Helpers to record a specific task information */
+void tracing_record_cmdline(struct task_struct *task)
+{
+	tracing_record_taskinfo(task, TRACE_RECORD_CMDLINE);
+}
+
+void tracing_record_tgid(struct task_struct *task)
+{
+	tracing_record_taskinfo(task, TRACE_RECORD_TGID);
 }
 
 /*
@@ -3144,7 +3217,7 @@ static void *s_start(struct seq_file *m, loff_t *pos)
 #endif
 
 	if (!iter->snapshot)
-		atomic_inc(&trace_record_cmdline_disabled);
+		atomic_inc(&trace_record_taskinfo_disabled);
 
 	if (*pos != iter->pos) {
 		iter->ent = NULL;
@@ -3189,7 +3262,7 @@ static void s_stop(struct seq_file *m, void *p)
 #endif
 
 	if (!iter->snapshot)
-		atomic_dec(&trace_record_cmdline_disabled);
+		atomic_dec(&trace_record_taskinfo_disabled);
 
 	trace_access_unlock(iter->cpu_file);
 	trace_event_read_unlock();
@@ -4236,6 +4309,18 @@ int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled)
 	if (mask == TRACE_ITER_RECORD_CMD)
 		trace_event_enable_cmd_record(enabled);
 
+	if (mask == TRACE_ITER_RECORD_TGID) {
+		if (!tgid_map)
+			tgid_map = kzalloc((PID_MAX_DEFAULT + 1) * sizeof(*tgid_map),
+					   GFP_KERNEL);
+		if (!tgid_map) {
+			tr->trace_flags &= ~TRACE_ITER_RECORD_TGID;
+			return -ENOMEM;
+		}
+
+		trace_event_enable_tgid_record(enabled);
+	}
+
 	if (mask == TRACE_ITER_EVENT_FORK)
 		trace_event_follow_fork(tr, enabled);
 

kernel/trace/trace.h

@@ -640,6 +640,9 @@ void set_graph_array(struct trace_array *tr);
 
 void tracing_start_cmdline_record(void);
 void tracing_stop_cmdline_record(void);
+void tracing_start_tgid_record(void);
+void tracing_stop_tgid_record(void);
+
 int register_tracer(struct tracer *type);
 int is_tracing_stopped(void);
 
@@ -700,6 +703,7 @@ static inline void __trace_stack(struct trace_array *tr, unsigned long flags,
 extern u64 ftrace_now(int cpu);
 
 extern void trace_find_cmdline(int pid, char comm[]);
+extern int trace_find_tgid(int pid);
 extern void trace_event_follow_fork(struct trace_array *tr, bool enable);
 
 #ifdef CONFIG_DYNAMIC_FTRACE
@@ -1124,6 +1128,7 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
 		C(CONTEXT_INFO,		"context-info"),   /* Print pid/cpu/time */ \
 		C(LATENCY_FMT,		"latency-format"),	\
 		C(RECORD_CMD,		"record-cmd"),		\
+		C(RECORD_TGID,		"record-tgid"),		\
 		C(OVERWRITE,		"overwrite"),		\
 		C(STOP_ON_FREE,		"disable_on_free"),	\
 		C(IRQ_INFO,		"irq-info"),		\
@@ -1440,6 +1445,8 @@ struct ftrace_event_field *
 trace_find_event_field(struct trace_event_call *call, char *name);
 
 extern void trace_event_enable_cmd_record(bool enable);
+extern void trace_event_enable_tgid_record(bool enable);
+
 extern int event_trace_add_tracer(struct dentry *parent, struct trace_array *tr);
 extern int event_trace_del_tracer(struct trace_array *tr);
 

kernel/trace/trace_events.c

@@ -343,6 +343,28 @@ void trace_event_enable_cmd_record(bool enable)
 	mutex_unlock(&event_mutex);
 }
 
+void trace_event_enable_tgid_record(bool enable)
+{
+	struct trace_event_file *file;
+	struct trace_array *tr;
+
+	mutex_lock(&event_mutex);
+	do_for_each_event_file(tr, file) {
+		if (!(file->flags & EVENT_FILE_FL_ENABLED))
+			continue;
+
+		if (enable) {
+			tracing_start_tgid_record();
+			set_bit(EVENT_FILE_FL_RECORDED_TGID_BIT, &file->flags);
+		} else {
+			tracing_stop_tgid_record();
+			clear_bit(EVENT_FILE_FL_RECORDED_TGID_BIT,
+				  &file->flags);
+		}
+	} while_for_each_event_file();
+	mutex_unlock(&event_mutex);
+}
+
 static int __ftrace_event_enable_disable(struct trace_event_file *file,
 					 int enable, int soft_disable)
 {
@@ -381,6 +403,12 @@ static int __ftrace_event_enable_disable(struct trace_event_file *file,
 				tracing_stop_cmdline_record();
 				clear_bit(EVENT_FILE_FL_RECORDED_CMD_BIT, &file->flags);
 			}
+
+			if (file->flags & EVENT_FILE_FL_RECORDED_TGID) {
+				tracing_stop_tgid_record();
+				clear_bit(EVENT_FILE_FL_RECORDED_CMD_BIT, &file->flags);
+			}
+
 			call->class->reg(call, TRACE_REG_UNREGISTER, file);
 		}
 		/* If in SOFT_MODE, just set the SOFT_DISABLE_BIT, else clear it */
@@ -407,18 +435,30 @@ static int __ftrace_event_enable_disable(struct trace_event_file *file,
 		}
 
 		if (!(file->flags & EVENT_FILE_FL_ENABLED)) {
+			bool cmd = false, tgid = false;
 
 			/* Keep the event disabled, when going to SOFT_MODE. */
 			if (soft_disable)
 				set_bit(EVENT_FILE_FL_SOFT_DISABLED_BIT, &file->flags);
 
 			if (tr->trace_flags & TRACE_ITER_RECORD_CMD) {
+				cmd = true;
 				tracing_start_cmdline_record();
 				set_bit(EVENT_FILE_FL_RECORDED_CMD_BIT, &file->flags);
 			}
+
+			if (tr->trace_flags & TRACE_ITER_RECORD_TGID) {
+				tgid = true;
+				tracing_start_tgid_record();
+				set_bit(EVENT_FILE_FL_RECORDED_TGID_BIT, &file->flags);
+			}
+
 			ret = call->class->reg(call, TRACE_REG_REGISTER, file);
 			if (ret) {
-				tracing_stop_cmdline_record();
+				if (cmd)
+					tracing_stop_cmdline_record();
+				if (tgid)
+					tracing_stop_tgid_record();
 				pr_info("event trace: Could not enable event "
 					"%s\n", trace_event_name(call));
 				break;