Add virtual LITMUS^RT control device.

This device only supports mmap()'ing a single page.
This page is shared RW between the kernel and userspace.
It is inteded to allow near-zero-overhead communication
between the kernel and userspace. It's first use will be a
proper implementation of user-signaled
non-preemptable section support.

1 files changed, 28 insertions, 7 deletions

diff --git a/litmus/litmus.c b/litmus/litmus.c
index d31a2ba030e4..589062f8ab87 100644
--- a/litmus/litmus.c
+++ b/litmus/litmus.c
@@ -268,12 +268,13 @@ asmlinkage long sys_null_call(cycles_t __user *ts)
 static void reinit_litmus_state(struct task_struct* p, int restore)
 {
         struct rt_task  user_config = {};
-        __user short   *np_flag     = NULL;
+        void*  ctrl_page     = NULL;
 
         if (restore) {
-                /* Safe user-space provided configuration data. */
+                /* Safe user-space provided configuration data.
+                 * and allocated page. */
                 user_config = p->rt_param.task_params;
-                np_flag     = p->rt_param.np_flag;
+                ctrl_page   = p->rt_param.ctrl_page;
         }
 
         /* We probably should not be inheriting any task's priority
@@ -282,7 +283,7 @@ static void reinit_litmus_state(struct task_struct* p, int restore)
         WARN_ON(p->rt_param.inh_task);
 
         /* We need to restore the priority of the task. */
-//      __setscheduler(p, p->rt_param.old_policy, p->rt_param.old_prio);
+//      __setscheduler(p, p->rt_param.old_policy, p->rt_param.old_prio); XXX why is this commented?
 
         /* Cleanup everything else. */
         memset(&p->rt_param, 0, sizeof(p->rt_param));
@@ -290,7 +291,7 @@ static void reinit_litmus_state(struct task_struct* p, int restore)
         /* Restore preserved fields. */
         if (restore) {
                 p->rt_param.task_params = user_config;
-                p->rt_param.np_flag      = np_flag;
+                p->rt_param.ctrl_page   = ctrl_page;
         }
 }
 
@@ -412,8 +413,11 @@ out:
 void litmus_fork(struct task_struct* p)
 {
         if (is_realtime(p))
-                /* clean out any litmus related state, don't preserve anything*/
+                /* clean out any litmus related state, don't preserve anything */
                 reinit_litmus_state(p, 0);
+        else
+                /* non-rt tasks might have ctrl_page set */
+                tsk_rt(p)->ctrl_page = NULL;
 }
 
 /* Called upon execve().
@@ -426,12 +430,29 @@ void litmus_exec(void)
 
         if (is_realtime(p)) {
                 WARN_ON(p->rt_param.inh_task);
-                p->rt_param.np_flag = NULL;
+                if (tsk_rt(p)->ctrl_page) {
+                        free_page((unsigned long) tsk_rt(p)->ctrl_page);
+                        tsk_rt(p)->ctrl_page = NULL;
+                }
         }
 }
 
 void exit_litmus(struct task_struct *dead_tsk)
 {
+        /* We also allow non-RT tasks to
+         * allocate control pages to allow
+         * measurements with non-RT tasks.
+         * So check if we need to free the page
+         * in any case.
+         */
+        if (tsk_rt(dead_tsk)->ctrl_page) {
+                TRACE_TASK(dead_tsk,
+                           "freeing ctrl_page %p\n",
+                           tsk_rt(dead_tsk)->ctrl_page);
+                free_page((unsigned long) tsk_rt(dead_tsk)->ctrl_page);
+        }
+
+        /* main cleanup only for RT tasks */
         if (is_realtime(dead_tsk))
                 litmus_exit_task(dead_tsk);
 }