tracing: Call on_each_cpu() when adding or removing single pids from set_event_pid

For the case where pids are already in set_event_pid, and one is added or
removed then each CPU should be checked to make sure that the new or old pid
is on or not on a CPU.

 For example:

 # echo 123 >> set_event_pid

or

 # echo '!123' >> set_event_pid

Link: http://lkml.kernel.org/r/20151030061643.GA19480@cac

Suggested-by: Jiaxing Wang <hello.wjx@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 7 insertions, 6 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index fb0261e90acc..292bccf3e011 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1729,14 +1729,15 @@ ftrace_event_pid_write(struct file *filp, const char __user *ubuf,
                                                  tr, INT_MAX);
                 register_trace_prio_sched_wakeup(event_filter_pid_sched_wakeup_probe_post,
                                                  tr, 0);
-
-                /*
-                 * Ignoring of pids is done at task switch. But we have to
-                 * check for those tasks that are currently running.
-                 */
-                on_each_cpu(ignore_task_cpu, tr, 1);
         }
 
+        /*
+         * Ignoring of pids is done at task switch. But we have to
+         * check for those tasks that are currently running.
+         * Always do this in case a pid was appended or removed.
+         */
+        on_each_cpu(ignore_task_cpu, tr, 1);
+
         mutex_unlock(&event_mutex);
 
         ret = read;