tracepoint, vfs, sched: Add exec() tracepoint

Added a minimal exec tracepoint. Exec is an important major event
in the life of a task, like fork(), clone() or exit(), all of
which we already trace.

[ We also do scheduling re-balancing during exec() - so it's useful
  from a scheduler instrumentation POV as well. ]

If you want to watch a task start up, when it gets exec'ed is a good place
to start.  With the addition of this tracepoint, exec's can be monitored
and better picture of general system activity can be obtained. This
tracepoint will also enable better process life tracking, allowing you to
answer questions like "what process keeps starting up binary X?".

This tracepoint can also be useful in ftrace filtering and trigger
conditions: i.e. starting or stopping filtering when exec is called.

Signed-off-by: David Smith <dsmith@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/4F314D19.7030504@redhat.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

fs/exec.c

@@ -63,6 +63,8 @@
 #include <trace/events/task.h>
 #include "internal.h"
 
+#include <trace/events/sched.h>
+
 int core_uses_pid;
 char core_pattern[CORENAME_MAX_SIZE] = "core";
 unsigned int core_pipe_limit;
@@ -1401,9 +1403,10 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
 			 */
 			bprm->recursion_depth = depth;
 			if (retval >= 0) {
-				if (depth == 0)
-					ptrace_event(PTRACE_EVENT_EXEC,
-							old_pid);
+				if (depth == 0) {
+					trace_sched_process_exec(current, old_pid, bprm);
+					ptrace_event(PTRACE_EVENT_EXEC, old_pid);
+				}
 				put_binfmt(fmt);
 				allow_write_access(bprm->file);
 				if (bprm->file)

include/trace/events/sched.h

@@ -6,6 +6,7 @@
 
 #include <linux/sched.h>
 #include <linux/tracepoint.h>
+#include <linux/binfmts.h>
 
 /*
  * Tracepoint for calling kthread_stop, performed to end a kthread:
@@ -275,6 +276,32 @@ TRACE_EVENT(sched_process_fork,
 		__entry->child_comm, __entry->child_pid)
 );
 
+/*
+ * Tracepoint for exec:
+ */
+TRACE_EVENT(sched_process_exec,
+
+	TP_PROTO(struct task_struct *p, pid_t old_pid,
+		 struct linux_binprm *bprm),
+
+	TP_ARGS(p, old_pid, bprm),
+
+	TP_STRUCT__entry(
+		__string(	filename,	bprm->filename	)
+		__field(	pid_t,		pid		)
+		__field(	pid_t,		old_pid		)
+	),
+
+	TP_fast_assign(
+		__assign_str(filename, bprm->filename);
+		__entry->pid		= p->pid;
+		__entry->old_pid	= p->pid;
+	),
+
+	TP_printk("filename=%s pid=%d old_pid=%d", __get_str(filename),
+		  __entry->pid, __entry->old_pid)
+);
+
 /*
  * XXX the below sched_stat tracepoints only apply to SCHED_OTHER/BATCH/IDLE
  *     adding sched_stat support to SCHED_FIFO/RR would be welcome.