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+/*
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+ * Read-Copy Update mechanism for mutual exclusion (tree-based version)
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+ * Internal non-public definitions that provide either classic
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+ * or preemptable semantics.
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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 Red Hat, 2009
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+ * Copyright IBM Corporation, 2009
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+ *
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+ * Author: Ingo Molnar <mingo@elte.hu>
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+ * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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+ */
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+
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+
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+#ifdef CONFIG_TREE_PREEMPT_RCU
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+
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+struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
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+DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
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+
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+/*
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+ * Tell them what RCU they are running.
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+ */
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+static inline void rcu_bootup_announce(void)
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+{
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+ printk(KERN_INFO
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+ "Experimental preemptable hierarchical RCU implementation.\n");
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+}
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+
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+/*
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+ * Return the number of RCU-preempt batches processed thus far
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+ * for debug and statistics.
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+ */
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+long rcu_batches_completed_preempt(void)
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+{
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+ return rcu_preempt_state.completed;
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+}
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+EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
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+
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+/*
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+ * Return the number of RCU batches processed thus far for debug & stats.
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+ */
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+long rcu_batches_completed(void)
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+{
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+ return rcu_batches_completed_preempt();
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+}
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+EXPORT_SYMBOL_GPL(rcu_batches_completed);
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+
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+/*
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+ * Record a preemptable-RCU quiescent state for the specified CPU. Note
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+ * that this just means that the task currently running on the CPU is
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+ * not in a quiescent state. There might be any number of tasks blocked
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+ * while in an RCU read-side critical section.
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+ */
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+static void rcu_preempt_qs_record(int cpu)
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+{
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+ struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
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+ rdp->passed_quiesc = 1;
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+ rdp->passed_quiesc_completed = rdp->completed;
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+}
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+
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+/*
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+ * We have entered the scheduler or are between softirqs in ksoftirqd.
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+ * If we are in an RCU read-side critical section, we need to reflect
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+ * that in the state of the rcu_node structure corresponding to this CPU.
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+ * Caller must disable hardirqs.
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+ */
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+static void rcu_preempt_qs(int cpu)
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+{
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+ struct task_struct *t = current;
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+ int phase;
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+ struct rcu_data *rdp;
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+ struct rcu_node *rnp;
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+
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+ if (t->rcu_read_lock_nesting &&
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+ (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
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+
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+ /* Possibly blocking in an RCU read-side critical section. */
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+ rdp = rcu_preempt_state.rda[cpu];
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+ rnp = rdp->mynode;
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+ spin_lock(&rnp->lock);
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+ t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
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+ t->rcu_blocked_cpu = cpu;
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+
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+ /*
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+ * If this CPU has already checked in, then this task
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+ * will hold up the next grace period rather than the
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+ * current grace period. Queue the task accordingly.
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+ * If the task is queued for the current grace period
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+ * (i.e., this CPU has not yet passed through a quiescent
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+ * state for the current grace period), then as long
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+ * as that task remains queued, the current grace period
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+ * cannot end.
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+ */
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+ phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1);
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+ list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);
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+ smp_mb(); /* Ensure later ctxt swtch seen after above. */
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+ spin_unlock(&rnp->lock);
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+ }
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+
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+ /*
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+ * Either we were not in an RCU read-side critical section to
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+ * begin with, or we have now recorded that critical section
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+ * globally. Either way, we can now note a quiescent state
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+ * for this CPU. Again, if we were in an RCU read-side critical
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+ * section, and if that critical section was blocking the current
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+ * grace period, then the fact that the task has been enqueued
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+ * means that we continue to block the current grace period.
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+ */
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+ rcu_preempt_qs_record(cpu);
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+ t->rcu_read_unlock_special &= ~(RCU_READ_UNLOCK_NEED_QS |
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+ RCU_READ_UNLOCK_GOT_QS);
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+}
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+
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+/*
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+ * Tree-preemptable RCU implementation for rcu_read_lock().
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+ * Just increment ->rcu_read_lock_nesting, shared state will be updated
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+ * if we block.
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+ */
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+void __rcu_read_lock(void)
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+{
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+ ACCESS_ONCE(current->rcu_read_lock_nesting)++;
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+ barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */
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+}
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+EXPORT_SYMBOL_GPL(__rcu_read_lock);
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+
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+static void rcu_read_unlock_special(struct task_struct *t)
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+{
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+ int empty;
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+ unsigned long flags;
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+ unsigned long mask;
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+ struct rcu_node *rnp;
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+ int special;
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+
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+ /* NMI handlers cannot block and cannot safely manipulate state. */
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+ if (in_nmi())
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+ return;
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+
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+ local_irq_save(flags);
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+
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+ /*
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+ * If RCU core is waiting for this CPU to exit critical section,
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+ * let it know that we have done so.
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+ */
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+ special = t->rcu_read_unlock_special;
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+ if (special & RCU_READ_UNLOCK_NEED_QS) {
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+ t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
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+ t->rcu_read_unlock_special |= RCU_READ_UNLOCK_GOT_QS;
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+ }
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+
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+ /* Hardware IRQ handlers cannot block. */
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+ if (in_irq()) {
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+ local_irq_restore(flags);
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+ return;
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+ }
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+
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+ /* Clean up if blocked during RCU read-side critical section. */
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+ if (special & RCU_READ_UNLOCK_BLOCKED) {
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+ t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
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+
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+ /* Remove this task from the list it blocked on. */
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+ rnp = rcu_preempt_state.rda[t->rcu_blocked_cpu]->mynode;
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+ spin_lock(&rnp->lock);
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+ empty = list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
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+ list_del_init(&t->rcu_node_entry);
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+ t->rcu_blocked_cpu = -1;
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+
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+ /*
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+ * If this was the last task on the current list, and if
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+ * we aren't waiting on any CPUs, report the quiescent state.
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+ * Note that both cpu_quiet_msk_finish() and cpu_quiet_msk()
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+ * drop rnp->lock and restore irq.
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+ */
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+ if (!empty && rnp->qsmask == 0 &&
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+ list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1])) {
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+ t->rcu_read_unlock_special &=
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+ ~(RCU_READ_UNLOCK_NEED_QS |
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+ RCU_READ_UNLOCK_GOT_QS);
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+ if (rnp->parent == NULL) {
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+ /* Only one rcu_node in the tree. */
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+ cpu_quiet_msk_finish(&rcu_preempt_state, flags);
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+ return;
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+ }
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+ /* Report up the rest of the hierarchy. */
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+ mask = rnp->grpmask;
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+ spin_unlock_irqrestore(&rnp->lock, flags);
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+ rnp = rnp->parent;
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+ spin_lock_irqsave(&rnp->lock, flags);
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+ cpu_quiet_msk(mask, &rcu_preempt_state, rnp, flags);
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+ return;
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+ }
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+ spin_unlock(&rnp->lock);
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+ }
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+ local_irq_restore(flags);
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+}
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+
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+/*
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+ * Tree-preemptable RCU implementation for rcu_read_unlock().
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+ * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
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+ * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
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+ * invoke rcu_read_unlock_special() to clean up after a context switch
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+ * in an RCU read-side critical section and other special cases.
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+ */
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+void __rcu_read_unlock(void)
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+{
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+ struct task_struct *t = current;
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+
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+ barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */
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+ if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
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+ unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
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+ rcu_read_unlock_special(t);
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+}
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+EXPORT_SYMBOL_GPL(__rcu_read_unlock);
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+
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+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
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+
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+/*
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+ * Scan the current list of tasks blocked within RCU read-side critical
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+ * sections, printing out the tid of each.
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+ */
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+static void rcu_print_task_stall(struct rcu_node *rnp)
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+{
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+ unsigned long flags;
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+ struct list_head *lp;
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+ int phase = rnp->gpnum & 0x1;
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+ struct task_struct *t;
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+
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+ if (!list_empty(&rnp->blocked_tasks[phase])) {
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+ spin_lock_irqsave(&rnp->lock, flags);
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+ phase = rnp->gpnum & 0x1; /* re-read under lock. */
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+ lp = &rnp->blocked_tasks[phase];
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+ list_for_each_entry(t, lp, rcu_node_entry)
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+ printk(" P%d", t->pid);
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+ spin_unlock_irqrestore(&rnp->lock, flags);
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+ }
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+}
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+
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+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
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+
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+/*
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+ * Check for preempted RCU readers for the specified rcu_node structure.
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+ * If the caller needs a reliable answer, it must hold the rcu_node's
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+ * >lock.
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+ */
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+static int rcu_preempted_readers(struct rcu_node *rnp)
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+{
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+ return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
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+}
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+
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+/*
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+ * Check for a quiescent state from the current CPU. When a task blocks,
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+ * the task is recorded in the corresponding CPU's rcu_node structure,
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+ * which is checked elsewhere.
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+ *
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+ * Caller must disable hard irqs.
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+ */
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+static void rcu_preempt_check_callbacks(int cpu)
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+{
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+ struct task_struct *t = current;
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+
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+ if (t->rcu_read_lock_nesting == 0) {
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+ t->rcu_read_unlock_special &=
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+ ~(RCU_READ_UNLOCK_NEED_QS | RCU_READ_UNLOCK_GOT_QS);
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+ rcu_preempt_qs_record(cpu);
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+ return;
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+ }
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+ if (per_cpu(rcu_preempt_data, cpu).qs_pending) {
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+ if (t->rcu_read_unlock_special & RCU_READ_UNLOCK_GOT_QS) {
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+ rcu_preempt_qs_record(cpu);
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+ t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_GOT_QS;
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+ } else if (!(t->rcu_read_unlock_special &
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+ RCU_READ_UNLOCK_NEED_QS)) {
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+ t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
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+ }
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+ }
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+}
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+
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+/*
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+ * Process callbacks for preemptable RCU.
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+ */
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+static void rcu_preempt_process_callbacks(void)
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+{
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+ __rcu_process_callbacks(&rcu_preempt_state,
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+ &__get_cpu_var(rcu_preempt_data));
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+}
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+
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+/*
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+ * Queue a preemptable-RCU callback for invocation after a grace period.
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+ */
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+void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
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+{
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+ __call_rcu(head, func, &rcu_preempt_state);
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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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+ * Check to see if there is any immediate preemptable-RCU-related work
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+ * to be done.
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+ */
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+static int rcu_preempt_pending(int cpu)
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+{
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+ return __rcu_pending(&rcu_preempt_state,
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+ &per_cpu(rcu_preempt_data, cpu));
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+}
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+
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+/*
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+ * Does preemptable RCU need the CPU to stay out of dynticks mode?
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+ */
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+static int rcu_preempt_needs_cpu(int cpu)
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+{
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+ return !!per_cpu(rcu_preempt_data, cpu).nxtlist;
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+}
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+
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+/*
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+ * Initialize preemptable RCU's per-CPU data.
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+ */
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+static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
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+{
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+ rcu_init_percpu_data(cpu, &rcu_preempt_state, 1);
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+}
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+
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+/*
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+ * Check for a task exiting while in a preemptable-RCU read-side
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+ * critical section, clean up if so. No need to issue warnings,
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+ * as debug_check_no_locks_held() already does this if lockdep
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+ * is enabled.
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+ */
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+void exit_rcu(void)
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+{
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+ struct task_struct *t = current;
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+
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+ if (t->rcu_read_lock_nesting == 0)
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+ return;
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+ t->rcu_read_lock_nesting = 1;
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+ rcu_read_unlock();
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+}
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+
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+#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
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+
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+/*
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+ * Tell them what RCU they are running.
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+ */
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+static inline void rcu_bootup_announce(void)
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+{
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+ printk(KERN_INFO "Hierarchical RCU implementation.\n");
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+}
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+
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+/*
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+ * Return the number of RCU batches processed thus far for debug & stats.
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+ */
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+long rcu_batches_completed(void)
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+{
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+ return rcu_batches_completed_sched();
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+}
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+EXPORT_SYMBOL_GPL(rcu_batches_completed);
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+
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+/*
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+ * Because preemptable RCU does not exist, we never have to check for
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+ * CPUs being in quiescent states.
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+ */
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+static void rcu_preempt_qs(int cpu)
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+{
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+}
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+
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+#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
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+
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+/*
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+ * Because preemptable RCU does not exist, we never have to check for
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+ * tasks blocked within RCU read-side critical sections.
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+ */
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+static void rcu_print_task_stall(struct rcu_node *rnp)
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+{
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+}
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+
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+#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
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+
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+/*
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+ * Because preemptable RCU does not exist, there are never any preempted
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+ * RCU readers.
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+ */
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+static int rcu_preempted_readers(struct rcu_node *rnp)
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+{
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+ return 0;
|
|
|
+}
|
|
|
+
|
|
|
+/*
|
|
|
+ * Because preemptable RCU does not exist, it never has any callbacks
|
|
|
+ * to check.
|
|
|
+ */
|
|
|
+void rcu_preempt_check_callbacks(int cpu)
|
|
|
+{
|
|
|
+}
|
|
|
+
|
|
|
+/*
|
|
|
+ * Because preemptable RCU does not exist, it never has any callbacks
|
|
|
+ * to process.
|
|
|
+ */
|
|
|
+void rcu_preempt_process_callbacks(void)
|
|
|
+{
|
|
|
+}
|
|
|
+
|
|
|
+/*
|
|
|
+ * In classic RCU, call_rcu() is just call_rcu_sched().
|
|
|
+ */
|
|
|
+void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
|
|
|
+{
|
|
|
+ call_rcu_sched(head, func);
|
|
|
+}
|
|
|
+EXPORT_SYMBOL_GPL(call_rcu);
|
|
|
+
|
|
|
+/*
|
|
|
+ * Because preemptable RCU does not exist, it never has any work to do.
|
|
|
+ */
|
|
|
+static int rcu_preempt_pending(int cpu)
|
|
|
+{
|
|
|
+ return 0;
|
|
|
+}
|
|
|
+
|
|
|
+/*
|
|
|
+ * Because preemptable RCU does not exist, it never needs any CPU.
|
|
|
+ */
|
|
|
+static int rcu_preempt_needs_cpu(int cpu)
|
|
|
+{
|
|
|
+ return 0;
|
|
|
+}
|
|
|
+
|
|
|
+/*
|
|
|
+ * Because preemptable RCU does not exist, there is no per-CPU
|
|
|
+ * data to initialize.
|
|
|
+ */
|
|
|
+static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
|
|
|
+{
|
|
|
+}
|
|
|
+
|
|
|
+#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
|
Paul E. McKenney