Initial Spring 2016 commit.

kern/thread/spinlock.c

@@ -0,0 +1,148 @@
+/*
+ * Copyright (c) 2009
+ *	The President and Fellows of Harvard College.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/* Make sure to build out-of-line versions of inline functions */
+#define SPINLOCK_INLINE   /* empty */
+#define MEMBAR_INLINE     /* empty */
+
+#include <types.h>
+#include <lib.h>
+#include <cpu.h>
+#include <spl.h>
+#include <spinlock.h>
+#include <membar.h>
+#include <current.h>	/* for curcpu */
+
+/*
+ * Spinlocks.
+ */
+
+
+/*
+ * Initialize spinlock.
+ */
+void
+spinlock_init(struct spinlock *splk)
+{
+	spinlock_data_set(&splk->splk_lock, 0);
+	splk->splk_holder = NULL;
+}
+
+/*
+ * Clean up spinlock.
+ */
+void
+spinlock_cleanup(struct spinlock *splk)
+{
+	KASSERT(splk->splk_holder == NULL);
+	KASSERT(spinlock_data_get(&splk->splk_lock) == 0);
+}
+
+/*
+ * Get the lock.
+ *
+ * First disable interrupts (otherwise, if we get a timer interrupt we
+ * might come back to this lock and deadlock), then use a machine-level
+ * atomic operation to wait for the lock to be free.
+ */
+void
+spinlock_acquire(struct spinlock *splk)
+{
+	struct cpu *mycpu;
+
+	splraise(IPL_NONE, IPL_HIGH);
+
+	/* this must work before curcpu initialization */
+	if (CURCPU_EXISTS()) {
+		mycpu = curcpu->c_self;
+		if (splk->splk_holder == mycpu) {
+			panic("Deadlock on spinlock %p\n", splk);
+		}
+		mycpu->c_spinlocks++;
+	}
+	else {
+		mycpu = NULL;
+	}
+
+	while (1) {
+		/*
+		 * Do test-test-and-set, that is, read first before
+		 * doing test-and-set, to reduce bus contention.
+		 *
+		 * Test-and-set is a machine-level atomic operation
+		 * that writes 1 into the lock word and returns the
+		 * previous value. If that value was 0, the lock was
+		 * previously unheld and we now own it. If it was 1,
+		 * we don't.
+		 */
+		if (spinlock_data_get(&splk->splk_lock) != 0) {
+			continue;
+		}
+		if (spinlock_data_testandset(&splk->splk_lock) != 0) {
+			continue;
+		}
+		break;
+	}
+
+	membar_store_any();
+	splk->splk_holder = mycpu;
+}
+
+/*
+ * Release the lock.
+ */
+void
+spinlock_release(struct spinlock *splk)
+{
+	/* this must work before curcpu initialization */
+	if (CURCPU_EXISTS()) {
+		KASSERT(splk->splk_holder == curcpu->c_self);
+		KASSERT(curcpu->c_spinlocks > 0);
+		curcpu->c_spinlocks--;
+	}
+
+	splk->splk_holder = NULL;
+	membar_any_store();
+	spinlock_data_set(&splk->splk_lock, 0);
+	spllower(IPL_HIGH, IPL_NONE);
+}
+
+/*
+ * Check if the current cpu holds the lock.
+ */
+bool
+spinlock_do_i_hold(struct spinlock *splk)
+{
+	if (!CURCPU_EXISTS()) {
+		return true;
+	}
+
+	/* Assume we can read splk_holder atomically enough for this to work */
+	return (splk->splk_holder == curcpu->c_self);
+}