Restructure pi_semaphore struct for generic inheritance framework.

First patch in a series to implement a generic priority inheritance
framework that can be used by semaphores that use priority inheritance.

This patch makes pi_semaphore a 'base class' for pi-protocols. pi_semaphore
is updated to include a pi_sem_record field named stack_node. This stack_node
is a linked-list node that a task holding the pi_semaphore instance adds to
their semaphore stack.  Note that the task's semaphore stack (or linked-list)
simply chains stack_node's of held semaphores into a single linked-list.
This is safe since there is only one semaphore holder at any given moment.

Finally, FMLP-specific data members out to child class fmlp_semaphore.

4 files changed, 56 insertions, 5 deletions

diff --git a/include/litmus/fdso.h b/include/litmus/fdso.h
index 61f1b5baf42c..b0e62a9098bd 100644
--- a/include/litmus/fdso.h
+++ b/include/litmus/fdso.h
@@ -62,7 +62,7 @@ static inline void* od_lookup(int od, obj_type_t type)
         return e && e->obj->type == type ? e->obj->obj : NULL;
 }
 
-#define lookup_fmlp_sem(od)((struct pi_semaphore*)  od_lookup(od, FMLP_SEM))
+#define lookup_fmlp_sem(od)((struct fmlp_semaphore*)  od_lookup(od, FMLP_SEM))
 #define lookup_srp_sem(od) ((struct srp_semaphore*) od_lookup(od, SRP_SEM))
 #define lookup_ics(od)     ((struct ics*)           od_lookup(od, ICS_ID))
 
diff --git a/include/litmus/rt_param.h b/include/litmus/rt_param.h
index a7a183f34a80..6f40b52f0802 100644
--- a/include/litmus/rt_param.h
+++ b/include/litmus/rt_param.h
@@ -92,6 +92,28 @@ struct rt_job {
         unsigned int    job_no;
 };
 
+#ifdef CONFIG_PI_SEMAPHORES
+/* Record for storing a held lock and associated priority inheritance.
+ * Records are stored in a linked-list stack to support priority
+ * inheritance of nested critical sections.
+ *
+ * When strung together in a stack, nodes provide a record
+ * of currently held semaphores and order in which they were
+ * acquired.
+ */
+struct pi_sem_record {
+        /* Pointer to inheritance-donating job.
+         * May be set to "self" if there is no active
+         * inheritance from this semaphore.
+         */
+        struct task_struct *inh_task;
+
+        struct list_head list;
+};
+
+typedef struct pi_sem_record pi_sem_record_t;
+#endif
+
 struct pfair_param;
 
 /*      RT task parameters for scheduling extensions
diff --git a/include/litmus/sched_plugin.h b/include/litmus/sched_plugin.h
index 9c1c9f28ba79..071e809564b2 100644
--- a/include/litmus/sched_plugin.h
+++ b/include/litmus/sched_plugin.h
@@ -7,6 +7,7 @@
 
 #include <linux/sched.h>
 
+#ifdef CONFIG_PI_SEMAPHORES
 /* struct for semaphore with priority inheritance */
 struct pi_semaphore {
         atomic_t count;
@@ -17,10 +18,29 @@ struct pi_semaphore {
                 struct task_struct *task;
                 struct task_struct* cpu_task[NR_CPUS];
         } hp;
+
+        /* lock stack */
+        struct pi_sem_record stack_node;
+};
+
+static inline struct pi_semaphore* to_pi(void *sem) {
+        return (struct pi_semaphore*)sem;
+}
+#endif
+
+#ifdef CONFIG_FMLP
+struct fmlp_semaphore {
+        struct pi_semaphore pi; /* must always be first. */
+
         /* current lock holder */
         struct task_struct *holder;
 };
 
+static inline struct fmlp_semaphore* to_fmlp(struct pi_semaphore* sem) {
+        return (struct fmlp_semaphore*)sem;
+}
+#endif
+
 /************************ setup/tear down ********************/
 
 typedef long (*activate_plugin_t) (void);
@@ -63,6 +83,7 @@ typedef void (*task_block_t)  (struct task_struct *task);
  */
 typedef void (*task_exit_t)    (struct task_struct *);
 
+#ifdef CONFIG_PI_SEMAPHORES
 /* Called when the new_owner is released from the wait queue
  * it should now inherit the priority from sem, _before_ it gets readded
  * to any queue
@@ -79,7 +100,7 @@ typedef long (*return_priority_t) (struct pi_semaphore *sem);
  * priority is higher than that of the current holder.
  */
 typedef long (*pi_block_t) (struct pi_semaphore *sem, struct task_struct *t);
-
+#endif
 
 
 
@@ -124,9 +145,9 @@ struct sched_plugin {
 #ifdef CONFIG_FMLP
         /*     priority inheritance     */
         unsigned int            fmlp_active;
-        inherit_priority_t      inherit_priority;
-        return_priority_t       return_priority;
-        pi_block_t              pi_block;
+        inherit_priority_t      fmlp_inherit_priority;
+        return_priority_t       fmlp_return_priority;
+        pi_block_t          fmlp_pi_block;
 #endif
 } __attribute__ ((__aligned__(SMP_CACHE_BYTES)));
 
diff --git a/litmus/Kconfig b/litmus/Kconfig
index 9888589ef126..e00887e672df 100644
--- a/litmus/Kconfig
+++ b/litmus/Kconfig
@@ -58,9 +58,17 @@ config SRP
           Say Yes if you want FMLP local long critical section
           synchronization support.
 
+config PI_SEMAPHORES
+        bool "Semaphores with Priority Inheritance"
+        default n
+        help
+          Generalized support for all Litmus priority inheriting semaphore
+          protocols.
+
 config FMLP
         bool "FMLP support"
         depends on NP_SECTION
+        depends on PI_SEMAPHORES
         default n
         help
           Include support for deterministic multiprocessor real-time