Implement basic sleeping locks for gnumach

* kern/atomic.h: New file.
* kern/kmutex.h: New file.
* kern/kmutex.c: New file.
* Makefrag.am (libkernel_a_SOURCES): Add atomic.h, kmutex.h, kmutex.c.
* kern/sched_prim.h (thread_wakeup_prim): Make it return boolean_t.
* kern/sched_prim.c (thread_wakeup_prim): Return TRUE if we woke a
thread, and FALSE otherwise.

5 files changed, 187 insertions, 2 deletions

diff --git a/kern/atomic.h b/kern/atomic.h
new file mode 100644
index 00000000..00da1645
--- /dev/null
+++ b/kern/atomic.h
@@ -0,0 +1,54 @@
+/* Copyright (C) 2017 Free Software Foundation, Inc.
+   Contributed by Agustina Arzille <avarzille@riseup.net>, 2017.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either
+   version 2 of the license, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public
+   License along with this program; if not, see
+   <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef _KERN_ATOMIC_H_
+#define _KERN_ATOMIC_H_   1
+
+/* Atomically compare *PTR with EXP and set it to NVAL if they're equal.
+ * Evaluates to a boolean, indicating whether the comparison was successful.*/
+#define __atomic_cas_helper(ptr, exp, nval, mo)   \
+  ({   \
+     typeof(exp) __e = (exp);   \
+     __atomic_compare_exchange_n ((ptr), &__e, (nval), 0,   \
+       __ATOMIC_##mo, __ATOMIC_RELAXED);   \
+   })
+
+#define atomic_cas_acq(ptr, exp, nval)   \
+  __atomic_cas_helper (ptr, exp, nval, ACQUIRE)
+
+#define atomic_cas_rel(ptr, exp, nval)   \
+  __atomic_cas_helper (ptr, exp, nval, RELEASE)
+
+#define atomic_cas_seq(ptr, exp, nval)   \
+  __atomic_cas_helper (ptr, exp, nval, SEQ_CST)
+
+/* Atomically exchange the value of *PTR with VAL, evaluating to
+ * its previous value. */
+#define __atomic_swap_helper(ptr, val, mo)   \
+  __atomic_exchange_n ((ptr), (val), __ATOMIC_##mo)
+
+#define atomic_swap_acq(ptr, val)   \
+  __atomic_swap_helper (ptr, val, ACQUIRE)
+
+#define atomic_swap_rel(ptr, val)   \
+  __atomic_swap_helper (ptr, val, RELEASE)
+
+#define atomic_swap_seq(ptr, val)   \
+  __atomic_swap_helper (ptr, val, SEQ_CST)
+
+#endif
diff --git a/kern/kmutex.c b/kern/kmutex.c
new file mode 100644
index 00000000..5926d1d9
--- /dev/null
+++ b/kern/kmutex.c
@@ -0,0 +1,76 @@
+/* Copyright (C) 2017 Free Software Foundation, Inc.
+   Contributed by Agustina Arzille <avarzille@riseup.net>, 2017.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either
+   version 2 of the license, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public
+   License along with this program; if not, see
+   <http://www.gnu.org/licenses/>.
+*/
+
+#include <kern/kmutex.h>
+#include <kern/atomic.h>
+#include <kern/sched_prim.h>
+#include <kern/thread.h>
+
+void kmutex_init (struct kmutex *mtxp)
+{
+  mtxp->state = KMUTEX_AVAIL;
+  simple_lock_init (&mtxp->lock);
+}
+
+kern_return_t kmutex_lock (struct kmutex *mtxp, boolean_t interruptible)
+{
+  check_simple_locks ();
+
+  if (atomic_cas_acq (&mtxp->state, KMUTEX_AVAIL, KMUTEX_LOCKED))
+    /* Unowned mutex - We're done. */
+    return (KERN_SUCCESS);
+
+  /* The mutex is locked. We may have to sleep. */
+  simple_lock (&mtxp->lock);
+  if (atomic_swap_acq (&mtxp->state, KMUTEX_CONTENDED) == KMUTEX_AVAIL)
+    {
+      /* The mutex was released in-between. */
+      simple_unlock (&mtxp->lock);
+      return (KERN_SUCCESS);
+    }
+
+  /* Sleep and check the result value of the waiting, in order to
+   * inform our caller if we were interrupted or not. Note that
+   * we don't need to set again the mutex state. The owner will
+   * handle that in every case. */
+  thread_sleep ((event_t)mtxp, (simple_lock_t)&mtxp->lock, interruptible);
+  return (current_thread()->wait_result == THREAD_AWAKENED ?
+    KERN_SUCCESS : KERN_INTERRUPTED);
+}
+
+kern_return_t kmutex_trylock (struct kmutex *mtxp)
+{
+  return (atomic_cas_acq (&mtxp->state, KMUTEX_AVAIL, KMUTEX_LOCKED) ?
+    KERN_SUCCESS : KERN_FAILURE);
+}
+
+void kmutex_unlock (struct kmutex *mtxp)
+{
+  if (atomic_cas_rel (&mtxp->state, KMUTEX_LOCKED, KMUTEX_AVAIL))
+    /* No waiters - We're done. */
+    return;
+
+  simple_lock (&mtxp->lock);
+
+  if (!thread_wakeup_one ((event_t)mtxp))
+    /* Any threads that were waiting on this mutex were
+     * interrupted and left - Reset the mutex state. */
+    mtxp->state = KMUTEX_AVAIL;
+
+  simple_unlock (&mtxp->lock);
+}
diff --git a/kern/kmutex.h b/kern/kmutex.h
new file mode 100644
index 00000000..29815156
--- /dev/null
+++ b/kern/kmutex.h
@@ -0,0 +1,52 @@
+/* Copyright (C) 2017 Free Software Foundation, Inc.
+   Contributed by Agustina Arzille <avarzille@riseup.net>, 2017.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either
+   version 2 of the license, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public
+   License along with this program; if not, see
+   <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef _KERN_KMUTEX_H_
+#define _KERN_KMUTEX_H_   1
+
+#include <kern/lock.h>
+#include <mach/kern_return.h>
+
+struct kmutex
+{
+  unsigned int state;
+  decl_simple_lock_data (, lock)
+};
+
+/* Possible values for the mutex state. */
+#define KMUTEX_AVAIL       0
+#define KMUTEX_LOCKED      1
+#define KMUTEX_CONTENDED   2
+
+/* Initialize mutex in *MTXP. */
+extern void kmutex_init (struct kmutex *mtxp);
+
+/* Acquire lock MTXP. If INTERRUPTIBLE is true, the sleep may be
+ * prematurely terminated, in which case the function returns
+ * KERN_INTERRUPTED. Otherwise, KERN_SUCCESS is returned. */
+extern kern_return_t kmutex_lock (struct kmutex *mtxp,
+  boolean_t interruptible);
+
+/* Try to acquire the lock MTXP without sleeping.
+ * Returns KERN_SUCCESS if successful, KERN_FAILURE otherwise. */
+extern kern_return_t kmutex_trylock (struct kmutex *mtxp);
+
+/* Unlock the mutex MTXP. */
+extern void kmutex_unlock (struct kmutex *mtxp);
+
+#endif
diff --git a/kern/sched_prim.c b/kern/sched_prim.c
index bb767352..173f0687 100644
--- a/kern/sched_prim.c
+++ b/kern/sched_prim.c
@@ -376,13 +376,14 @@ void clear_wait(
  *	and thread_wakeup_one.
  *
  */
-void thread_wakeup_prim(
+boolean_t thread_wakeup_prim(
 	event_t		event,
 	boolean_t	one_thread,
 	int		result)
 {
 	queue_t			q;
 	int			index;
+	boolean_t woke = FALSE;
 	thread_t		thread, next_th;
 	decl_simple_lock_data( , *lock);
 	spl_t			s;
@@ -435,6 +436,7 @@ void thread_wakeup_prim(
 				break;
 			}
 			thread_unlock(thread);
+			woke = TRUE;
 			if (one_thread)
 				break;
 		}
@@ -442,6 +444,7 @@ void thread_wakeup_prim(
 	}
 	simple_unlock(lock);
 	splx(s);
+	return (woke);
 }
 
 /*
diff --git a/kern/sched_prim.h b/kern/sched_prim.h
index dfb2f54b..405e5456 100644
--- a/kern/sched_prim.h
+++ b/kern/sched_prim.h
@@ -72,7 +72,7 @@ extern void	thread_sleep(
 	simple_lock_t	lock,
 	boolean_t	interruptible);
 extern void	thread_wakeup(void);		/* for function pointers */
-extern void	thread_wakeup_prim(
+extern boolean_t	thread_wakeup_prim(
 	event_t		event,
 	boolean_t	one_thread,
 	int		result);