[PATCH] tracing: Fix issues recording task information

[Joel Fernandes]

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-t...@android.com
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Ingo Molnar <mi...@redhat.com>
Reported-by: Michael Sartain <mikes...@gmail.com>
Signed-off-by: Joel Fernandes <joe...@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