6 files changed, 81 insertions, 39 deletions

diff --git a/litmus/Kconfig b/litmus/Kconfig
index 95e0671e2aec..c5dbc4a176ae 100644
--- a/litmus/Kconfig
+++ b/litmus/Kconfig
@@ -34,6 +34,37 @@ config RELEASE_MASTER
            (http://www.cs.unc.edu/~anderson/papers.html).
            Currently only supported by GSN-EDF.
 
+config REALTIME_AUX_TASKS
+        bool "Real-Time Auxillary Tasks"
+        depends on LITMUS_LOCKING
+        default n
+        help
+                Adds a system call that forces all non-real-time threads in a process
+                to become auxillary real-time tasks. These tasks inherit the priority of
+                the highest-prio *BLOCKED* real-time task (non-auxillary) in the process.
+                This allows the integration of COTS code that has background helper threads
+                used primarily for message passing and synchronization. If these
+                background threads are NOT real-time scheduled, then unbounded priority
+                inversions may occur if a real-time task blocks on a non-real-time thread.
+
+                Beware of the following pitfalls:
+                  1) Auxillary threads should not be CPU intensive. They should mostly
+                     block on mutexes and condition variables. Violating this will
+                         likely prevent meaningful analysis.
+                  2) Since there may be more than one auxillary thread per process,
+                     priority inversions may occur with respect to single-threaded
+                         task models if/when one of threads are scheduled simultanously
+                         with another of the same identity.
+                  3) Busy-wait deadlock is likely between normal real-time tasks and
+                     auxillary tasks synchronize using _preemptive_ spinlocks that do
+                         not use priority inheritance.
+
+                These pitfalls are mitgated by the fact that auxillary tasks only
+                inherit priorities from blocked tasks (Blocking signifies that the
+                blocked task _may_ be waiting on an auxillary task to perform some
+                work.). Futher, auxillary tasks without an inherited priority are
+                _always_ scheduled with a priority less than any normal real-time task!!
+
 endmenu
 
 menu "Real-Time Synchronization"
diff --git a/litmus/Makefile b/litmus/Makefile
index f2dd7be7ae4a..67d8b8ee72bc 100644
--- a/litmus/Makefile
+++ b/litmus/Makefile
@@ -18,6 +18,7 @@ obj-y     = sched_plugin.o litmus.o \
             bheap.o \
             binheap.o \
             ctrldev.o \
+                aux_tasks.o \
             sched_gsn_edf.o \
             sched_psn_edf.o \
             sched_pfp.o
@@ -31,7 +32,7 @@ obj-$(CONFIG_SCHED_TASK_TRACE) += sched_task_trace.o
 obj-$(CONFIG_SCHED_DEBUG_TRACE) += sched_trace.o
 obj-$(CONFIG_SCHED_OVERHEAD_TRACE) += trace.o
 
-obj-$(CONFIG_LITMUS_LOCKING) += aux_tasks.o kfmlp_lock.o
+obj-$(CONFIG_LITMUS_LOCKING) += kfmlp_lock.o
 obj-$(CONFIG_LITMUS_NESTED_LOCKING) += rsm_lock.o ikglp_lock.o
 obj-$(CONFIG_LITMUS_SOFTIRQD) += litmus_softirq.o
 obj-$(CONFIG_LITMUS_PAI_SOFTIRQD) += litmus_pai_softirq.o
diff --git a/litmus/aux_tasks.c b/litmus/aux_tasks.c
index 5057137bbbea..b0617accdf7f 100644
--- a/litmus/aux_tasks.c
+++ b/litmus/aux_tasks.c
@@ -1,8 +1,8 @@
-#ifdef CONFIG_LITMUS_LOCKING
-
 #include <litmus/sched_plugin.h>
 #include <litmus/trace.h>
 #include <litmus/litmus.h>
+
+#ifdef CONFIG_REALTIME_AUX_TASKS
 #include <litmus/rt_param.h>
 #include <litmus/aux_tasks.h>
 
@@ -23,14 +23,11 @@ static int admit_aux_task(struct task_struct *t)
          * fail-safe.
          */
         struct rt_task tp = {
-                //.period = MAGIC_AUX_TASK_PERIOD,
-                //.relative_deadline = MAGIC_AUX_TASK_PERIOD,
-                .period = 1000000,   /* has to wait 1 ms before it can run again once it has exhausted budget */
+                .period = 1000000,   /* 1ms */
                 .relative_deadline = 1000000,
                 .exec_cost = 1000000, /* allow full utilization */
                 .phase = 0,
                 .cpu = task_cpu(leader),  /* take CPU of group leader */
-                //.budget_policy = NO_ENFORCEMENT,
                 .budget_policy = QUANTUM_ENFORCEMENT,
                 .budget_signal_policy = NO_SIGNALS,
                 .cls = RT_CLASS_BEST_EFFORT
@@ -280,7 +277,7 @@ static int aux_task_owner_max_priority_order(struct binheap_node *a,
 }
 
 
-static long __do_enable_slave_non_rt_threads(void)
+static long __do_enable_aux_tasks(void)
 {
         long retval = 0;
         struct task_struct *leader;
@@ -344,7 +341,7 @@ static long __do_enable_slave_non_rt_threads(void)
         return retval;
 }
 
-static long __do_disable_slave_non_rt_threads(void)
+static long __do_disable_aux_tasks(void)
 {
         long retval = 0;
         struct task_struct *leader;
@@ -385,17 +382,17 @@ static long __do_disable_slave_non_rt_threads(void)
         return retval;
 }
 
-asmlinkage long sys_slave_non_rt_threads(int enable)
+asmlinkage long sys_set_aux_tasks(int enable)
 {
         long retval;
 
         read_lock_irq(&tasklist_lock);
 
         if (enable) {
-                retval = __do_enable_slave_non_rt_threads();
+                retval = __do_enable_aux_tasks();
         }
         else {
-                retval = __do_disable_slave_non_rt_threads();
+                retval = __do_disable_aux_tasks();
         }
 
         read_unlock_irq(&tasklist_lock);
@@ -405,9 +402,9 @@ asmlinkage long sys_slave_non_rt_threads(int enable)
 
 #else
 
-asmlinkage long sys_slave_non_rt_tasks(int enable)
+asmlinkage long sys_set_aux_tasks(int enable)
 {
-        printk("Unsupported. Recompile with CONFIG_LITMUS_LOCKING.\n");
+        printk("Unsupported. Recompile with CONFIG_REALTIME_AUX_TASKS.\n");
         return -EINVAL;
 }
 
diff --git a/litmus/edf_common.c b/litmus/edf_common.c
index ca06f6ec103e..7e0d3a5d0c4d 100644
--- a/litmus/edf_common.c
+++ b/litmus/edf_common.c
@@ -22,7 +22,7 @@
 #include <litmus/fpmath.h>
 #endif
 
-//#ifdef CONFIG_EDF_TIE_BREAK_HASH
+#if defined(CONFIG_EDF_TIE_BREAK_HASH) || defined(CONFIG_REALTIME_AUX_TASKS)
 #include <linux/hash.h>
 static inline long edf_hash(struct task_struct *t)
 {
@@ -41,8 +41,9 @@ static inline long edf_hash(struct task_struct *t)
          */
         return hash_32(hash_32((u32)tsk_rt(t)->job_params.job_no, 32) ^ t->pid, 32);
 }
-//#endif
+#endif
 
+#ifdef CONFIG_REALTIME_AUX_TASKS
 int aux_tie_break(struct task_struct *first, struct task_struct *second)
 {
         long fhash = edf_hash(first);
@@ -57,6 +58,7 @@ int aux_tie_break(struct task_struct *first, struct task_struct *second)
         }
         return 0;
 }
+#endif
 
 
 /* edf_higher_prio -  returns true if first has a higher EDF priority
@@ -75,11 +77,6 @@ int edf_higher_prio(struct task_struct* first, struct task_struct* second)
         struct task_struct *first_task = first;
         struct task_struct *second_task = second;
 
-        int first_lo_aux;
-        int second_lo_aux;
-        int first_hi_aux;
-        int second_hi_aux;
-
         /* There is no point in comparing a task to itself. */
         if (first && first == second) {
                 TRACE_CUR("WARNING: pointless edf priority comparison: %s/%d\n", first->comm, first->pid);
@@ -93,8 +90,14 @@ int edf_higher_prio(struct task_struct* first, struct task_struct* second)
                 return first && !second;
         }
 
-#ifdef CONFIG_LITMUS_LOCKING
+#ifdef CONFIG_REALTIME_AUX_TASKS
+        {
+        /* statically prioritize all auxillary tasks that have no inheritance
+         * below all other regular real-time tasks.
+         */
 
+        int first_lo_aux, second_lo_aux;
+        int first_hi_aux, second_hi_aux;
         first_lo_aux = first->rt_param.is_aux_task && !first->rt_param.inh_task;
         second_lo_aux = second->rt_param.is_aux_task && !second->rt_param.inh_task;
 
@@ -120,8 +123,10 @@ int edf_higher_prio(struct task_struct* first, struct task_struct* second)
                 TRACE_CUR("hi aux tie break: %s/%d >> %s/%d --- %d\n", first->comm, first->pid, second->comm, second->pid, aux_hi_tie_break);
                 return aux_hi_tie_break;
         }
+        }
+#endif
 
-
+#ifdef CONFIG_LITMUS_LOCKING
         /* Check for EFFECTIVE priorities. Change task
          * used for comparison in such a case.
          */
@@ -233,11 +238,13 @@ int edf_higher_prio(struct task_struct* first, struct task_struct* second)
                                         return 1;
                                 }
 #endif
+
+#ifdef CONFIG_REALTIME_AUX_TASKS
+                                /* is this dead code? */
                                 if (tsk_rt(first)->is_aux_task < tsk_rt(second)->is_aux_task) {
-                                        TRACE_CUR("AUX BREAK!\n");
                                         return 1;
                                 }
-
+#endif
 
                                 /* Something could be wrong if you get this far. */
                                 if (unlikely(first->rt_param.inh_task ==
diff --git a/litmus/litmus.c b/litmus/litmus.c
index e2bf2a7ad01b..d368202ab8c3 100644
--- a/litmus/litmus.c
+++ b/litmus/litmus.c
@@ -25,7 +25,7 @@
 #include <litmus/nvidia_info.h>
 #endif
 
-#ifdef CONFIG_LITMUS_LOCKING
+#ifdef CONFIG_REALTIME_AUX_TASKS
 #include <litmus/aux_tasks.h>
 #endif
 
@@ -413,7 +413,7 @@ static void reinit_litmus_state(struct task_struct* p, int restore)
         /* Cleanup everything else. */
         memset(&p->rt_param, 0, sizeof(p->rt_param));
 
-#ifdef CONFIG_LITMUS_LOCKING
+#ifdef CONFIG_REALTIME_AUX_TASKS
         /* also clear out the aux_data. the !restore case is only called on
          * fork (initial thread creation). */
         if (!restore)
@@ -623,10 +623,6 @@ void litmus_fork(struct task_struct* p)
                 tsk_rt(p)->ctrl_page = NULL;
 
                 reinit_litmus_state(p, 0);
-
-                /* still don't inherit any parental parameters */
-                //memset(&p->rt_param, 0, sizeof(p->rt_param));
-                //memset(&p->aux_data, 0, sizeof(p->aux_data));
         }
 
         /* od tables are never inherited across a fork */
diff --git a/litmus/sched_gsn_edf.c b/litmus/sched_gsn_edf.c
index 270e06c20bbf..5fc330f14a0e 100644
--- a/litmus/sched_gsn_edf.c
+++ b/litmus/sched_gsn_edf.c
@@ -29,7 +29,6 @@
 
 #ifdef CONFIG_LITMUS_LOCKING
 #include <litmus/kfmlp_lock.h>
-#include <litmus/aux_tasks.h>
 #endif
 
 #ifdef CONFIG_LITMUS_NESTED_LOCKING
@@ -41,6 +40,10 @@
 #include <litmus/affinity.h>
 #endif
 
+#ifdef CONFIG_REALTIME_AUX_TASKS
+#include <litmus/aux_tasks.h>
+#endif
+
 #ifdef CONFIG_LITMUS_SOFTIRQD
 #include <litmus/litmus_softirq.h>
 #endif
@@ -313,15 +316,15 @@ static noinline void requeue(struct task_struct* task)
         BUG_ON(is_queued(task));
 
         if (is_released(task, litmus_clock())) {
-
+#ifdef CONFIG_REALTIME_AUX_TASKS
                 if (unlikely(tsk_rt(task)->is_aux_task && !is_running(task))) {
                         /* aux_task probably transitioned to real-time while it was blocked */
                         TRACE_CUR("aux task %s/%d is not ready!\n", task->comm, task->pid);
                         unlink(task); /* really needed? */
                 }
-                else {
+                else
+#endif
                         __add_ready(&gsnedf, task);
-                }
         }
         else {
                 /* it has got to wait */
@@ -1046,11 +1049,12 @@ static void gsnedf_task_wake_up(struct task_struct *task)
         set_rt_flags(task, RT_F_RUNNING);
 #endif
 
+#ifdef CONFIG_REALTIME_AUX_TASKS
         if (tsk_rt(task)->has_aux_tasks) {
-
                 TRACE_CUR("%s/%d is ready so aux tasks may not inherit.\n", task->comm, task->pid);
                 disable_aux_task_owner(task);
         }
+#endif
 
         gsnedf_job_arrival(task);
         raw_spin_unlock_irqrestore(&gsnedf_lock, flags);
@@ -1067,11 +1071,13 @@ static void gsnedf_task_block(struct task_struct *t)
 
         unlink(t);
 
+#ifdef CONFIG_REALTIME_AUX_TASKS
         if (tsk_rt(t)->has_aux_tasks) {
 
                 TRACE_CUR("%s/%d is blocked so aux tasks may inherit.\n", t->comm, t->pid);
                 enable_aux_task_owner(t);
         }
+#endif
 
         raw_spin_unlock_irqrestore(&gsnedf_lock, flags);
 
@@ -1087,7 +1093,7 @@ static void gsnedf_task_exit(struct task_struct * t)
         gsnedf_change_prio_pai_tasklet(t, NULL);
 #endif
 
-#ifdef CONFIG_LITMUS_LOCKING
+#ifdef CONFIG_REALTIME_AUX_TASKS
         if (tsk_rt(t)->is_aux_task) {
                 exit_aux_task(t); /* cannot be called with gsnedf_lock held */
         }
@@ -1096,7 +1102,7 @@ static void gsnedf_task_exit(struct task_struct * t)
         /* unlink if necessary */
         raw_spin_lock_irqsave(&gsnedf_lock, flags);
 
-#ifdef CONFIG_LITMUS_LOCKING
+#ifdef CONFIG_REALTIME_AUX_TASKS
         /* make sure we clean up on our way out */
         if(tsk_rt(t)->has_aux_tasks) {
                 disable_aux_task_owner(t); /* must be called witl gsnedf_lock held */
@@ -1209,11 +1215,12 @@ static int __increase_priority_inheritance(struct task_struct* t,
                                 check_for_preemptions();
                         }
 
-
+#ifdef CONFIG_REALTIME_AUX_TASKS
                         /* propagate to aux tasks */
                         if (tsk_rt(t)->has_aux_tasks) {
                                 aux_task_owner_increase_priority(t);
                         }
+#endif
                 }
 #ifdef CONFIG_LITMUS_NESTED_LOCKING
         }
@@ -1319,10 +1326,13 @@ static int __decrease_priority_inheritance(struct task_struct* t,
                         raw_spin_unlock(&gsnedf.release_lock);
                 }
 
+#ifdef CONFIG_REALTIME_AUX_TASKS
                 /* propagate to aux tasks */
                 if (tsk_rt(t)->has_aux_tasks) {
                         aux_task_owner_decrease_priority(t);
                 }
+#endif
+
 #ifdef CONFIG_LITMUS_NESTED_LOCKING
         }
         else {