tracing: Clean up scheduling in trace_wakeup_test_thread()

Peter's new debugging tool triggers when tasks exit with !TASK_RUNNING.
The code in trace_wakeup_test_thread() also has a single schedule() call
that should be encompassed by a loop.

This cleans up the code a little to make it a bit more robust and
also makes the return exit properly with TASK_RUNNING.

Link: http://lkml.kernel.org/p/20141008135216.76142204@gandalf.local.home
Reported-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Peter Zijlstra <peterz@infreadead.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index 5ef6049..593f52b 100644 (file)
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -1025,6 +1025,12 @@ trace_selftest_startup_nop(struct tracer *trace, struct trace_array *tr)
 #endif
 
 #ifdef CONFIG_SCHED_TRACER
+
+struct wakeup_test_data {
+       struct completion       is_ready;
+       int                     go;
+};
+
 static int trace_wakeup_test_thread(void *data)
 {
        /* Make this a -deadline thread */
@@ -1034,51 +1040,56 @@ static int trace_wakeup_test_thread(void *data)
                .sched_deadline = 10000000ULL,
                .sched_period = 10000000ULL
        };
-       struct completion *x = data;
+       struct wakeup_test_data *x = data;
 
        sched_setattr(current, &attr);
 
        /* Make it know we have a new prio */
-       complete(x);
+       complete(&x->is_ready);
 
        /* now go to sleep and let the test wake us up */
        set_current_state(TASK_INTERRUPTIBLE);
-       schedule();
+       while (!x->go) {
+               schedule();
+               set_current_state(TASK_INTERRUPTIBLE);
+       }
 
-       complete(x);
+       complete(&x->is_ready);
+
+       set_current_state(TASK_INTERRUPTIBLE);
 
        /* we are awake, now wait to disappear */
        while (!kthread_should_stop()) {
-               /*
-                * This will likely be the system top priority
-                * task, do short sleeps to let others run.
-                */
-               msleep(100);
+               schedule();
+               set_current_state(TASK_INTERRUPTIBLE);
        }
 
+       __set_current_state(TASK_RUNNING);
+
        return 0;
 }
-
 int
 trace_selftest_startup_wakeup(struct tracer *trace, struct trace_array *tr)
 {
        unsigned long save_max = tr->max_latency;
        struct task_struct *p;
-       struct completion is_ready;
+       struct wakeup_test_data data;
        unsigned long count;
        int ret;
 
-       init_completion(&is_ready);
+       memset(&data, 0, sizeof(data));
+
+       init_completion(&data.is_ready);
 
        /* create a -deadline thread */
-       p = kthread_run(trace_wakeup_test_thread, &is_ready, "ftrace-test");
+       p = kthread_run(trace_wakeup_test_thread, &data, "ftrace-test");
        if (IS_ERR(p)) {
                printk(KERN_CONT "Failed to create ftrace wakeup test thread ");
                return -1;
        }
 
        /* make sure the thread is running at -deadline policy */
-       wait_for_completion(&is_ready);
+       wait_for_completion(&data.is_ready);
 
        /* start the tracing */
        ret = tracer_init(trace, tr);
@@ -1099,18 +1110,20 @@ trace_selftest_startup_wakeup(struct tracer *trace, struct trace_array *tr)
                msleep(100);
        }
 
-       init_completion(&is_ready);
+       init_completion(&data.is_ready);
+
+       data.go = 1;
+       /* memory barrier is in the wake_up_process() */
 
        wake_up_process(p);
 
        /* Wait for the task to wake up */
-       wait_for_completion(&is_ready);
+       wait_for_completion(&data.is_ready);
 
        /* stop the tracing. */
        tracing_stop();
        /* check both trace buffers */
        ret = trace_test_buffer(&tr->trace_buffer, NULL);
-       printk("ret = %d\n", ret);
        if (!ret)
                ret = trace_test_buffer(&tr->max_buffer, &count);