[PATCH] tracing: Fix issues recording task information

[Joel Fernandes <joelaf@google.com>]

Currently we stop recording task information if any of them error out or are
not being recorded. Further if switching to/from the idle thread, we bail out
early on. Fix these issues.

Cc: kernel-team@android.com
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Reported-by: Michael Sartain <mikesart@gmail.com>
Signed-off-by: Joel Fernandes <joelaf@google.com>
---
Hi Steve,
This fix is based on ftrace/core branch at:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
Could you pick it up for -rc cycle if it looks good to you? Thanks.

 kernel/trace/trace.c | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index b66a1c8805f3..27b981a46389 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1918,7 +1918,11 @@ static int trace_save_cmdline(struct task_struct *tsk)
 {
 	unsigned pid, idx;
 
-	if (!tsk->pid || unlikely(tsk->pid > PID_MAX_DEFAULT))
+	/* treat recording of idle task as a success */
+	if (!tsk->pid)
+		return 1;
+
+	if (unlikely(tsk->pid > PID_MAX_DEFAULT))
 		return 0;
 
 	/*
@@ -2004,7 +2008,11 @@ int trace_find_tgid(int pid)
 
 static int trace_save_tgid(struct task_struct *tsk)
 {
-	if (unlikely(!tgid_map || !tsk->pid || tsk->pid > PID_MAX_DEFAULT))
+	/* treat recording of idle task as a success */
+	if (!tsk->pid)
+		return 1;
+
+	if (unlikely(!tgid_map || tsk->pid > PID_MAX_DEFAULT))
 		return 0;
 
 	tgid_map[tsk->pid] = tsk->tgid;
@@ -2031,11 +2039,14 @@ static bool tracing_record_taskinfo_skip(int flags)
  */
 void tracing_record_taskinfo(struct task_struct *task, int flags)
 {
+	bool done;
+
 	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))
+
+	done = !(flags & TRACE_RECORD_CMDLINE) || trace_save_cmdline(task);
+	done &= !(flags & TRACE_RECORD_TGID) || trace_save_tgid(task);
+	if (!done)
 		return;
 
 	__this_cpu_write(trace_taskinfo_save, false);
@@ -2052,15 +2063,16 @@ 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)
 {
-	if (tracing_record_taskinfo_skip(flags))
-		return;
+	bool done;
 
-	if ((flags & TRACE_RECORD_CMDLINE) &&
-	    (!trace_save_cmdline(prev) || !trace_save_cmdline(next)))
+	if (tracing_record_taskinfo_skip(flags))
 		return;
 
-	if ((flags & TRACE_RECORD_TGID) &&
-	    (!trace_save_tgid(prev) || !trace_save_tgid(next)))
+	done  = !(flags & TRACE_RECORD_CMDLINE) || trace_save_cmdline(prev);
+	done &= !(flags & TRACE_RECORD_CMDLINE) || trace_save_cmdline(next);
+	done &= !(flags & TRACE_RECORD_TGID) || trace_save_tgid(prev);
+	done &= !(flags & TRACE_RECORD_TGID) || trace_save_tgid(next);
+	if (!done)
 		return;
 
 	__this_cpu_write(trace_taskinfo_save, false);
-- 
2.13.2.725.g09c95d1e9-goog