From f4d75d0cd8424c17521d520fd9018ea22b7daaad Mon Sep 17 00:00:00 2001
From: Richard Braun <rbraun@sceen.net>
Date: Sat, 4 Mar 2017 16:27:05 +0100
Subject: kern/mutex: implement the --enable-mutex-pi option

This option turns all regular mutexes into real-time mutexes.
---
 INSTALL            |  5 +++++
 configure.ac       | 10 ++++++++++
 kern/mutex.c       |  4 ++++
 kern/mutex.h       | 46 +++++++++++++++++++++++++++++++++++++++++++++-
 kern/mutex_i.h     |  3 +++
 kern/mutex_types.h | 16 ++++++++++++++++
 6 files changed, 83 insertions(+), 1 deletion(-)

diff --git a/INSTALL b/INSTALL
index f9042109..97dcd148 100644
--- a/INSTALL
+++ b/INSTALL
@@ -243,6 +243,11 @@ X15 Options
      in a file named `test_pmap_update_mp.c' would be selected with the
      option `--enable-test-module=pmap_update_mp'.
 
+`--enable-mutex-pi'
+     Enable priority inheritance for regular mutexes (note that priority
+     inheritance is always enabled for real-time mutexes).
+     TODO Thoroughly describe the implications of this option
+
 `--with-max-cpus=MAX_CPUS'
      Set the maximum number of supported processors.
 
diff --git a/configure.ac b/configure.ac
index 023140bd..8c5b64a9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -34,6 +34,12 @@ AC_ARG_WITH([max-cpus],
             [opt_max_cpus=$withval],
             [opt_max_cpus=128])
 
+AC_ARG_ENABLE([mutex-pi],
+              [AS_HELP_STRING([--enable-mutex-pi],
+                              [enable priority inheritance for regular mutexes
+                               (note that priority inheritance is always
+                                enabled for real-time mutexes)])])
+
 AC_DEFINE([__KERNEL__], [1], [kernel code])
 AC_DEFINE_UNQUOTED([ARCH], [$arch], [arch])
 
@@ -74,6 +80,10 @@ AC_DEFINE_UNQUOTED([MAX_CPUS], [$opt_max_cpus],
                    [maximum number of supported processors])
 AC_MSG_NOTICE([maximum number of supported processors: $opt_max_cpus])
 
+AS_IF([test x"$enable_mutex_pi" = xyes],
+      [AC_DEFINE_UNQUOTED([X15_MUTEX_PI], [],
+                          [Enable priority inheritance for regular mutexes])])
+
 AH_BOTTOM([#include <kern/config.h>])
 AC_CONFIG_HEADER([config.h])
 AC_CONFIG_FILES([Makefile])
diff --git a/kern/mutex.c b/kern/mutex.c
index 1a1c2ea7..6a1af208 100644
--- a/kern/mutex.c
+++ b/kern/mutex.c
@@ -15,6 +15,8 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#ifndef X15_MUTEX_PI
+
 #include <stddef.h>
 
 #include <kern/mutex.h>
@@ -62,3 +64,5 @@ mutex_unlock_slow(struct mutex *mutex)
 
     sleepq_release(sleepq);
 }
+
+#endif /* X15_MUTEX_PI */
diff --git a/kern/mutex.h b/kern/mutex.h
index 2804fc44..c8ae4639 100644
--- a/kern/mutex.h
+++ b/kern/mutex.h
@@ -25,10 +25,52 @@
 #ifndef _KERN_MUTEX_H
 #define _KERN_MUTEX_H
 
+#include <kern/mutex_types.h>
+
+#ifdef X15_MUTEX_PI
+
+#include <kern/rtmutex.h>
+
+struct mutex;
+
+#define mutex_assert_locked(mutex) rtmutex_assert_locked(&(mutex)->rtmutex)
+
+static inline void
+mutex_init(struct mutex *mutex)
+{
+    rtmutex_init(&mutex->rtmutex);
+}
+
+static inline int
+mutex_trylock(struct mutex *mutex)
+{
+    return rtmutex_trylock(&mutex->rtmutex);
+}
+
+static inline void
+mutex_lock(struct mutex *mutex)
+{
+    rtmutex_lock(&mutex->rtmutex);
+}
+
+static inline void
+mutex_unlock(struct mutex *mutex)
+{
+    rtmutex_unlock(&mutex->rtmutex);
+
+    /*
+     * If this mutex was used along with a condition variable, wake up
+     * a potential pending waiter. This must be done after the mutex is
+     * unlocked so that a higher priority thread can directly acquire it.
+     */
+    thread_wakeup_last_cond();
+}
+
+#else /* X15_MUTEX_PI */
+
 #include <kern/assert.h>
 #include <kern/error.h>
 #include <kern/mutex_i.h>
-#include <kern/mutex_types.h>
 #include <kern/thread.h>
 
 struct mutex;
@@ -114,4 +156,6 @@ mutex_unlock(struct mutex *mutex)
     thread_wakeup_last_cond();
 }
 
+#endif /* X15_MUTEX_PI */
+
 #endif /* _KERN_MUTEX_H */
diff --git a/kern/mutex_i.h b/kern/mutex_i.h
index a161b1bb..158d8f7f 100644
--- a/kern/mutex_i.h
+++ b/kern/mutex_i.h
@@ -18,6 +18,8 @@
 #ifndef _KERN_MUTEX_I_H
 #define _KERN_MUTEX_I_H
 
+#ifndef X15_MUTEX_PI
+
 #include <kern/assert.h>
 #include <kern/mutex_types.h>
 #include <machine/atomic.h>
@@ -46,5 +48,6 @@ void mutex_lock_slow(struct mutex *mutex);
 
 void mutex_unlock_slow(struct mutex *mutex);
 
+#endif /* X15_MUTEX_PI */
 
 #endif /* _KERN_MUTEX_I_H */
diff --git a/kern/mutex_types.h b/kern/mutex_types.h
index e3126b10..4b7947fc 100644
--- a/kern/mutex_types.h
+++ b/kern/mutex_types.h
@@ -21,8 +21,24 @@
 #ifndef _KERN_MUTEX_TYPES_H
 #define _KERN_MUTEX_TYPES_H
 
+#ifdef X15_MUTEX_PI
+
+#include <kern/rtmutex_types.h>
+
+/*
+ * Do not directly alias rtmutex to make sure they cannot be used
+ * with condition variables by mistake.
+ */
+struct mutex {
+    struct rtmutex rtmutex;
+};
+
+#else /* X15_MUTEX_PI */
+
 struct mutex {
     unsigned int state;
 };
 
+#endif /* X15_MUTEX_PI */
+
 #endif /* _KERN_MUTEX_TYPES_H */
-- 
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