Initial Spring 2016 commit.

kern/thread/spl.c

@@ -0,0 +1,160 @@
+/*
+ * 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 spl inline functions */
+#define SPL_INLINE	/* empty */
+
+#include <types.h>
+#include <lib.h>
+#include <cpu.h>
+#include <spl.h>
+#include <thread.h>
+#include <current.h>
+
+/*
+ * Machine-independent interrupt handling functions.
+ *
+ * Traditionally, all this code is machine-dependent.
+ *
+ * However.
+ *
+ * Since on OS/161 we don't support interrupt levels on any platform,
+ * all we require under this logic is cpu_irqoff() and cpu_irqon()
+ * that explicitly turn interrupts off and on.
+ *
+ * If we had multiple interrupt levels, the number of levels would in
+ * general be different on different platforms (depending on hardware
+ * requirements and hardware capabilities) so things would get more
+ * complicated -- but nearly all of this code could remain MI.
+ */
+
+
+/*
+ * Raise and lower the interrupt priority level.
+ *
+ * Each spinlock acquisition can raise and lower the priority level
+ * independently. The spl calls also raise and lower the priority
+ * level independently of the spinlocks. This is necessary because in
+ * general spinlock acquisitions and releases don't nest perfectly,
+ * and don't necessarily nest with respect to spl calls either.
+ *
+ * For example:
+ *
+ *    struct spinlock red, blue;
+ *    int s;
+ *
+ *    spinlock_acquire(&red);
+ *    s = splhigh();
+ *    spinlock_acquire(&blue);
+ *    splx(s);
+ *    spinlock_release(&red);
+ *    spinlock_release(&blue);
+ *
+ * In order to make this work we need to count the number of times
+ * IPL_HIGH (or, if we had multiple interrupt priority levels, each
+ * level independently) has been raised. Interrupts go off on the
+ * first raise, and go on again only on the last lower.
+ *
+ * curthread->t_iplhigh_count is used to track this.
+ */
+void
+splraise(int oldspl, int newspl)
+{
+	struct thread *cur = curthread;
+
+	/* only one priority level, only one valid args configuration */
+	KASSERT(oldspl == IPL_NONE);
+	KASSERT(newspl == IPL_HIGH);
+
+	if (!CURCPU_EXISTS()) {
+		/* before curcpu initialization; interrupts are off anyway */
+		return;
+	}
+
+	if (cur->t_iplhigh_count == 0) {
+		cpu_irqoff();
+	}
+	cur->t_iplhigh_count++;
+}
+
+void
+spllower(int oldspl, int newspl)
+{
+	struct thread *cur = curthread;
+
+	/* only one priority level, only one valid args configuration */
+	KASSERT(oldspl == IPL_HIGH);
+	KASSERT(newspl == IPL_NONE);
+
+	if (!CURCPU_EXISTS()) {
+		/* before curcpu initialization; interrupts are off anyway */
+		return;
+	}
+
+	cur->t_iplhigh_count--;
+	if (cur->t_iplhigh_count == 0) {
+		cpu_irqon();
+	}
+}
+
+
+/*
+ * Disable or enable interrupts and adjust curspl setting. Return old
+ * spl level.
+ */
+int
+splx(int spl)
+{
+	struct thread *cur = curthread;
+	int ret;
+
+	if (!CURCPU_EXISTS()) {
+		/* before curcpu initialization; interrupts are off anyway */
+		return spl;
+	}
+
+	if (cur->t_curspl < spl) {
+		/* turning interrupts off */
+		splraise(cur->t_curspl, spl);
+		ret = cur->t_curspl;
+		cur->t_curspl = spl;
+	}
+	else if (cur->t_curspl > spl) {
+		/* turning interrupts on */
+		ret = cur->t_curspl;
+		cur->t_curspl = spl;
+		spllower(ret, spl);
+	}
+	else {
+		/* do nothing */
+		ret = spl;
+	}
+
+	return ret;
+}