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+/*
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+ * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
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+ *
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+ * This program is free software; you can redistribute it and/or modify
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+ * it under the terms of the GNU General Public License as published by
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+ * the Free Software Foundation; either version 2 of the License, or
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+ * (at your option) any later version.
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+ *
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+ * This program is distributed in the hope that it will be useful,
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+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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+ * GNU General Public License for more details.
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+ *
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+ * You should have received a copy of the GNU General Public License
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+ * along with this program; if not, write to the Free Software
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+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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+ *
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+ * Copyright IBM Corporation, 2008
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+ *
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+ * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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+ *
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+ * For detailed explanation of Read-Copy Update mechanism see -
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+ * Documentation/RCU
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+ */
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+
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+#include <linux/types.h>
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+#include <linux/kernel.h>
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+#include <linux/init.h>
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+#include <linux/rcupdate.h>
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+#include <linux/interrupt.h>
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+#include <linux/sched.h>
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+#include <linux/module.h>
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+#include <linux/completion.h>
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+#include <linux/moduleparam.h>
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+#include <linux/notifier.h>
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+#include <linux/cpu.h>
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+#include <linux/mutex.h>
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+#include <linux/time.h>
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+
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+/* Global control variables for rcupdate callback mechanism. */
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+struct rcu_ctrlblk {
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+ struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
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+ struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
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+ struct rcu_head **curtail; /* ->next pointer of last CB. */
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+};
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+
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+/* Definition for rcupdate control block. */
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+static struct rcu_ctrlblk rcu_ctrlblk = {
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+ .rcucblist = NULL,
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+ .donetail = &rcu_ctrlblk.rcucblist,
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+ .curtail = &rcu_ctrlblk.rcucblist,
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+};
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+static struct rcu_ctrlblk rcu_bh_ctrlblk = {
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+ .rcucblist = NULL,
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+ .donetail = &rcu_bh_ctrlblk.rcucblist,
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+ .curtail = &rcu_bh_ctrlblk.rcucblist,
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+};
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+
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+#ifdef CONFIG_NO_HZ
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+
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+static long rcu_dynticks_nesting = 1;
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+
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+/*
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+ * Enter dynticks-idle mode, which is an extended quiescent state
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+ * if we have fully entered that mode (i.e., if the new value of
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+ * dynticks_nesting is zero).
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+ */
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+void rcu_enter_nohz(void)
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+{
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+ if (--rcu_dynticks_nesting == 0)
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+ rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
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+}
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+
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+/*
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+ * Exit dynticks-idle mode, so that we are no longer in an extended
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+ * quiescent state.
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+ */
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+void rcu_exit_nohz(void)
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+{
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+ rcu_dynticks_nesting++;
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+}
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+
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+#endif /* #ifdef CONFIG_NO_HZ */
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+
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+/*
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+ * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
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+ * Also disable irqs to avoid confusion due to interrupt handlers invoking
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+ * call_rcu().
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+ */
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+static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
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+{
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+ unsigned long flags;
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+
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+ local_irq_save(flags);
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+ if (rcp->rcucblist != NULL &&
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+ rcp->donetail != rcp->curtail) {
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+ rcp->donetail = rcp->curtail;
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+ local_irq_restore(flags);
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+ return 1;
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+ }
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+ local_irq_restore(flags);
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+ return 0;
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+}
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+
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+/*
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+ * Record an rcu quiescent state. And an rcu_bh quiescent state while we
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+ * are at it, given that any rcu quiescent state is also an rcu_bh
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+ * quiescent state. Use "+" instead of "||" to defeat short circuiting.
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+ */
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+void rcu_sched_qs(int cpu)
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+{
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+ if (rcu_qsctr_help(&rcu_ctrlblk) + rcu_qsctr_help(&rcu_bh_ctrlblk))
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+ raise_softirq(RCU_SOFTIRQ);
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+}
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+
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+/*
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+ * Record an rcu_bh quiescent state.
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+ */
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+void rcu_bh_qs(int cpu)
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+{
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+ if (rcu_qsctr_help(&rcu_bh_ctrlblk))
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+ raise_softirq(RCU_SOFTIRQ);
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+}
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+
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+/*
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+ * Check to see if the scheduling-clock interrupt came from an extended
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+ * quiescent state, and, if so, tell RCU about it.
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+ */
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+void rcu_check_callbacks(int cpu, int user)
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+{
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+ if (user ||
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+ (idle_cpu(cpu) &&
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+ !in_softirq() &&
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+ hardirq_count() <= (1 << HARDIRQ_SHIFT)))
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+ rcu_sched_qs(cpu);
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+ else if (!in_softirq())
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+ rcu_bh_qs(cpu);
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+}
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+
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+/*
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+ * Helper function for rcu_process_callbacks() that operates on the
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+ * specified rcu_ctrlkblk structure.
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+ */
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+static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
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+{
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+ unsigned long flags;
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+ struct rcu_head *next, *list;
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+
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+ /* If no RCU callbacks ready to invoke, just return. */
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+ if (&rcp->rcucblist == rcp->donetail)
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+ return;
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+
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+ /* Move the ready-to-invoke callbacks to a local list. */
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+ local_irq_save(flags);
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+ list = rcp->rcucblist;
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+ rcp->rcucblist = *rcp->donetail;
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+ *rcp->donetail = NULL;
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+ if (rcp->curtail == rcp->donetail)
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+ rcp->curtail = &rcp->rcucblist;
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+ rcp->donetail = &rcp->rcucblist;
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+ local_irq_restore(flags);
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+
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+ /* Invoke the callbacks on the local list. */
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+ while (list) {
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+ next = list->next;
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+ prefetch(next);
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+ list->func(list);
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+ list = next;
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+ }
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+}
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+
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+/*
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+ * Invoke any callbacks whose grace period has completed.
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+ */
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+static void rcu_process_callbacks(struct softirq_action *unused)
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+{
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+ __rcu_process_callbacks(&rcu_ctrlblk);
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+ __rcu_process_callbacks(&rcu_bh_ctrlblk);
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+}
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+
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+/*
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+ * Null function to handle CPU being onlined. Longer term, we want to
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+ * make TINY_RCU avoid using rcupdate.c, but later...
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+ */
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+int rcu_cpu_notify(struct notifier_block *self,
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+ unsigned long action, void *hcpu)
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+{
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+ return NOTIFY_OK;
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+}
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+
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+/*
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+ * Wait for a grace period to elapse. But it is illegal to invoke
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+ * synchronize_sched() from within an RCU read-side critical section.
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+ * Therefore, any legal call to synchronize_sched() is a quiescent
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+ * state, and so on a UP system, synchronize_sched() need do nothing.
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+ * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
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+ * benefits of doing might_sleep() to reduce latency.)
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+ *
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+ * Cool, huh? (Due to Josh Triplett.)
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+ *
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+ * But we want to make this a static inline later.
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+ */
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+void synchronize_sched(void)
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+{
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+ cond_resched();
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+}
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+EXPORT_SYMBOL_GPL(synchronize_sched);
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+
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+void synchronize_rcu_bh(void)
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+{
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+ synchronize_sched();
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+}
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+EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
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+
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+/*
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+ * Helper function for call_rcu() and call_rcu_bh().
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+ */
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+static void __call_rcu(struct rcu_head *head,
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+ void (*func)(struct rcu_head *rcu),
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+ struct rcu_ctrlblk *rcp)
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+{
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+ unsigned long flags;
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+
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+ head->func = func;
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+ head->next = NULL;
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+ local_irq_save(flags);
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+ *rcp->curtail = head;
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+ rcp->curtail = &head->next;
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+ local_irq_restore(flags);
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+}
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+
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+/*
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+ * Post an RCU callback to be invoked after the end of an RCU grace
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+ * period. But since we have but one CPU, that would be after any
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+ * quiescent state.
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+ */
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+void call_rcu(struct rcu_head *head,
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+ void (*func)(struct rcu_head *rcu))
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+{
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+ __call_rcu(head, func, &rcu_ctrlblk);
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+}
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+EXPORT_SYMBOL_GPL(call_rcu);
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+
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+/*
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+ * Post an RCU bottom-half callback to be invoked after any subsequent
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+ * quiescent state.
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+ */
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+void call_rcu_bh(struct rcu_head *head,
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+ void (*func)(struct rcu_head *rcu))
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+{
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+ __call_rcu(head, func, &rcu_bh_ctrlblk);
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+}
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+EXPORT_SYMBOL_GPL(call_rcu_bh);
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+
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+void rcu_barrier(void)
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+{
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+ struct rcu_synchronize rcu;
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+
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+ init_completion(&rcu.completion);
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+ /* Will wake me after RCU finished. */
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+ call_rcu(&rcu.head, wakeme_after_rcu);
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+ /* Wait for it. */
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+ wait_for_completion(&rcu.completion);
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+}
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+EXPORT_SYMBOL_GPL(rcu_barrier);
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+
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+void rcu_barrier_bh(void)
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+{
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+ struct rcu_synchronize rcu;
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+
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+ init_completion(&rcu.completion);
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+ /* Will wake me after RCU finished. */
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+ call_rcu_bh(&rcu.head, wakeme_after_rcu);
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+ /* Wait for it. */
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+ wait_for_completion(&rcu.completion);
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+}
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+EXPORT_SYMBOL_GPL(rcu_barrier_bh);
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+
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+void rcu_barrier_sched(void)
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+{
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+ struct rcu_synchronize rcu;
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+
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+ init_completion(&rcu.completion);
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+ /* Will wake me after RCU finished. */
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+ call_rcu_sched(&rcu.head, wakeme_after_rcu);
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+ /* Wait for it. */
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+ wait_for_completion(&rcu.completion);
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+}
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+EXPORT_SYMBOL_GPL(rcu_barrier_sched);
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+
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+void __rcu_init(void)
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+{
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+ open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
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+}
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Paul E. McKenney