* Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*/
+#include <linux/delay.h>
#ifdef CONFIG_TREE_PREEMPT_RCU
struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
+static int rcu_preempted_readers_exp(struct rcu_node *rnp);
+
/*
* Tell them what RCU they are running.
*/
-static inline void rcu_bootup_announce(void)
+static void __init rcu_bootup_announce(void)
{
printk(KERN_INFO
"Experimental preemptable hierarchical RCU implementation.\n");
static void rcu_preempt_qs(int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
- rdp->passed_quiesc_completed = rdp->completed;
+ rdp->passed_quiesc_completed = rdp->gpnum - 1;
barrier();
rdp->passed_quiesc = 1;
}
*/
static int rcu_preempted_readers(struct rcu_node *rnp)
{
- return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
+ int phase = rnp->gpnum & 0x1;
+
+ return !list_empty(&rnp->blocked_tasks[phase]) ||
+ !list_empty(&rnp->blocked_tasks[phase + 2]);
+}
+
+/*
+ * Record a quiescent state for all tasks that were previously queued
+ * on the specified rcu_node structure and that were blocking the current
+ * RCU grace period. The caller must hold the specified rnp->lock with
+ * irqs disabled, and this lock is released upon return, but irqs remain
+ * disabled.
+ */
+static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
+ __releases(rnp->lock)
+{
+ unsigned long mask;
+ struct rcu_node *rnp_p;
+
+ if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) {
+ spin_unlock_irqrestore(&rnp->lock, flags);
+ return; /* Still need more quiescent states! */
+ }
+
+ rnp_p = rnp->parent;
+ if (rnp_p == NULL) {
+ /*
+ * Either there is only one rcu_node in the tree,
+ * or tasks were kicked up to root rcu_node due to
+ * CPUs going offline.
+ */
+ rcu_report_qs_rsp(&rcu_preempt_state, flags);
+ return;
+ }
+
+ /* Report up the rest of the hierarchy. */
+ mask = rnp->grpmask;
+ spin_unlock(&rnp->lock); /* irqs remain disabled. */
+ spin_lock(&rnp_p->lock); /* irqs already disabled. */
+ rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
}
+/*
+ * Handle special cases during rcu_read_unlock(), such as needing to
+ * notify RCU core processing or task having blocked during the RCU
+ * read-side critical section.
+ */
static void rcu_read_unlock_special(struct task_struct *t)
{
int empty;
+ int empty_exp;
unsigned long flags;
- unsigned long mask;
struct rcu_node *rnp;
int special;
spin_unlock(&rnp->lock); /* irqs remain disabled. */
}
empty = !rcu_preempted_readers(rnp);
+ empty_exp = !rcu_preempted_readers_exp(rnp);
+ smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
list_del_init(&t->rcu_node_entry);
t->rcu_blocked_node = NULL;
/*
* If this was the last task on the current list, and if
* we aren't waiting on any CPUs, report the quiescent state.
- * Note that both cpu_quiet_msk_finish() and cpu_quiet_msk()
- * drop rnp->lock and restore irq.
+ * Note that rcu_report_unblock_qs_rnp() releases rnp->lock.
*/
- if (!empty && rnp->qsmask == 0 &&
- !rcu_preempted_readers(rnp)) {
- struct rcu_node *rnp_p;
-
- if (rnp->parent == NULL) {
- /* Only one rcu_node in the tree. */
- cpu_quiet_msk_finish(&rcu_preempt_state, flags);
- return;
- }
- /* Report up the rest of the hierarchy. */
- mask = rnp->grpmask;
+ if (empty)
spin_unlock_irqrestore(&rnp->lock, flags);
- rnp_p = rnp->parent;
- spin_lock_irqsave(&rnp_p->lock, flags);
- WARN_ON_ONCE(rnp->qsmask);
- cpu_quiet_msk(mask, &rcu_preempt_state, rnp_p, flags);
- return;
- }
- spin_unlock(&rnp->lock);
+ else
+ rcu_report_unblock_qs_rnp(rnp, flags);
+
+ /*
+ * If this was the last task on the expedited lists,
+ * then we need to report up the rcu_node hierarchy.
+ */
+ if (!empty_exp && !rcu_preempted_readers_exp(rnp))
+ rcu_report_exp_rnp(&rcu_preempt_state, rnp);
+ } else {
+ local_irq_restore(flags);
}
- local_irq_restore(flags);
}
/*
* rcu_node. The reason for not just moving them to the immediate
* parent is to remove the need for rcu_read_unlock_special() to
* make more than two attempts to acquire the target rcu_node's lock.
+ * Returns true if there were tasks blocking the current RCU grace
+ * period.
+ *
+ * Returns 1 if there was previously a task blocking the current grace
+ * period on the specified rcu_node structure.
*
* The caller must hold rnp->lock with irqs disabled.
*/
-static void rcu_preempt_offline_tasks(struct rcu_state *rsp,
- struct rcu_node *rnp,
- struct rcu_data *rdp)
+static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
+ struct rcu_node *rnp,
+ struct rcu_data *rdp)
{
int i;
struct list_head *lp;
struct list_head *lp_root;
+ int retval = 0;
struct rcu_node *rnp_root = rcu_get_root(rsp);
struct task_struct *tp;
if (rnp == rnp_root) {
WARN_ONCE(1, "Last CPU thought to be offlined?");
- return; /* Shouldn't happen: at least one CPU online. */
+ return 0; /* Shouldn't happen: at least one CPU online. */
}
WARN_ON_ONCE(rnp != rdp->mynode &&
(!list_empty(&rnp->blocked_tasks[0]) ||
- !list_empty(&rnp->blocked_tasks[1])));
+ !list_empty(&rnp->blocked_tasks[1]) ||
+ !list_empty(&rnp->blocked_tasks[2]) ||
+ !list_empty(&rnp->blocked_tasks[3])));
/*
* Move tasks up to root rcu_node. Rely on the fact that the
* rcu_nodes in terms of gp_num value. This fact allows us to
* move the blocked_tasks[] array directly, element by element.
*/
- for (i = 0; i < 2; i++) {
+ if (rcu_preempted_readers(rnp))
+ retval |= RCU_OFL_TASKS_NORM_GP;
+ if (rcu_preempted_readers_exp(rnp))
+ retval |= RCU_OFL_TASKS_EXP_GP;
+ for (i = 0; i < 4; i++) {
lp = &rnp->blocked_tasks[i];
lp_root = &rnp_root->blocked_tasks[i];
while (!list_empty(lp)) {
spin_unlock(&rnp_root->lock); /* irqs remain disabled */
}
}
+ return retval;
}
/*
}
EXPORT_SYMBOL_GPL(call_rcu);
+/**
+ * synchronize_rcu - wait until a grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full grace
+ * period has elapsed, in other words after all currently executing RCU
+ * read-side critical sections have completed. RCU read-side critical
+ * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
+ * and may be nested.
+ */
+void synchronize_rcu(void)
+{
+ struct rcu_synchronize rcu;
+
+ if (!rcu_scheduler_active)
+ return;
+
+ init_completion(&rcu.completion);
+ /* Will wake me after RCU finished. */
+ call_rcu(&rcu.head, wakeme_after_rcu);
+ /* Wait for it. */
+ wait_for_completion(&rcu.completion);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu);
+
+static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
+static long sync_rcu_preempt_exp_count;
+static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
+
+/*
+ * Return non-zero if there are any tasks in RCU read-side critical
+ * sections blocking the current preemptible-RCU expedited grace period.
+ * If there is no preemptible-RCU expedited grace period currently in
+ * progress, returns zero unconditionally.
+ */
+static int rcu_preempted_readers_exp(struct rcu_node *rnp)
+{
+ return !list_empty(&rnp->blocked_tasks[2]) ||
+ !list_empty(&rnp->blocked_tasks[3]);
+}
+
+/*
+ * return non-zero if there is no RCU expedited grace period in progress
+ * for the specified rcu_node structure, in other words, if all CPUs and
+ * tasks covered by the specified rcu_node structure have done their bit
+ * for the current expedited grace period. Works only for preemptible
+ * RCU -- other RCU implementation use other means.
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex.
+ */
+static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
+{
+ return !rcu_preempted_readers_exp(rnp) &&
+ ACCESS_ONCE(rnp->expmask) == 0;
+}
+
+/*
+ * Report the exit from RCU read-side critical section for the last task
+ * that queued itself during or before the current expedited preemptible-RCU
+ * grace period. This event is reported either to the rcu_node structure on
+ * which the task was queued or to one of that rcu_node structure's ancestors,
+ * recursively up the tree. (Calm down, calm down, we do the recursion
+ * iteratively!)
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex.
+ */
+static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+ unsigned long flags;
+ unsigned long mask;
+
+ spin_lock_irqsave(&rnp->lock, flags);
+ for (;;) {
+ if (!sync_rcu_preempt_exp_done(rnp))
+ break;
+ if (rnp->parent == NULL) {
+ wake_up(&sync_rcu_preempt_exp_wq);
+ break;
+ }
+ mask = rnp->grpmask;
+ spin_unlock(&rnp->lock); /* irqs remain disabled */
+ rnp = rnp->parent;
+ spin_lock(&rnp->lock); /* irqs already disabled */
+ rnp->expmask &= ~mask;
+ }
+ spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+/*
+ * Snapshot the tasks blocking the newly started preemptible-RCU expedited
+ * grace period for the specified rcu_node structure. If there are no such
+ * tasks, report it up the rcu_node hierarchy.
+ *
+ * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
+ */
+static void
+sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+ int must_wait;
+
+ spin_lock(&rnp->lock); /* irqs already disabled */
+ list_splice_init(&rnp->blocked_tasks[0], &rnp->blocked_tasks[2]);
+ list_splice_init(&rnp->blocked_tasks[1], &rnp->blocked_tasks[3]);
+ must_wait = rcu_preempted_readers_exp(rnp);
+ spin_unlock(&rnp->lock); /* irqs remain disabled */
+ if (!must_wait)
+ rcu_report_exp_rnp(rsp, rnp);
+}
+
+/*
+ * Wait for an rcu-preempt grace period, but expedite it. The basic idea
+ * is to invoke synchronize_sched_expedited() to push all the tasks to
+ * the ->blocked_tasks[] lists, move all entries from the first set of
+ * ->blocked_tasks[] lists to the second set, and finally wait for this
+ * second set to drain.
+ */
+void synchronize_rcu_expedited(void)
+{
+ unsigned long flags;
+ struct rcu_node *rnp;
+ struct rcu_state *rsp = &rcu_preempt_state;
+ long snap;
+ int trycount = 0;
+
+ smp_mb(); /* Caller's modifications seen first by other CPUs. */
+ snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
+ smp_mb(); /* Above access cannot bleed into critical section. */
+
+ /*
+ * Acquire lock, falling back to synchronize_rcu() if too many
+ * lock-acquisition failures. Of course, if someone does the
+ * expedited grace period for us, just leave.
+ */
+ while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
+ if (trycount++ < 10)
+ udelay(trycount * num_online_cpus());
+ else {
+ synchronize_rcu();
+ return;
+ }
+ if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
+ goto mb_ret; /* Others did our work for us. */
+ }
+ if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
+ goto unlock_mb_ret; /* Others did our work for us. */
+
+ /* force all RCU readers onto blocked_tasks[]. */
+ synchronize_sched_expedited();
+
+ spin_lock_irqsave(&rsp->onofflock, flags);
+
+ /* Initialize ->expmask for all non-leaf rcu_node structures. */
+ rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
+ spin_lock(&rnp->lock); /* irqs already disabled. */
+ rnp->expmask = rnp->qsmaskinit;
+ spin_unlock(&rnp->lock); /* irqs remain disabled. */
+ }
+
+ /* Snapshot current state of ->blocked_tasks[] lists. */
+ rcu_for_each_leaf_node(rsp, rnp)
+ sync_rcu_preempt_exp_init(rsp, rnp);
+ if (NUM_RCU_NODES > 1)
+ sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
+
+ spin_unlock_irqrestore(&rsp->onofflock, flags);
+
+ /* Wait for snapshotted ->blocked_tasks[] lists to drain. */
+ rnp = rcu_get_root(rsp);
+ wait_event(sync_rcu_preempt_exp_wq,
+ sync_rcu_preempt_exp_done(rnp));
+
+ /* Clean up and exit. */
+ smp_mb(); /* ensure expedited GP seen before counter increment. */
+ ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
+unlock_mb_ret:
+ mutex_unlock(&sync_rcu_preempt_exp_mutex);
+mb_ret:
+ smp_mb(); /* ensure subsequent action seen after grace period. */
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
/*
* Check to see if there is any immediate preemptable-RCU-related work
* to be done.
/*
* Tell them what RCU they are running.
*/
-static inline void rcu_bootup_announce(void)
+static void __init rcu_bootup_announce(void)
{
printk(KERN_INFO "Hierarchical RCU implementation.\n");
}
return 0;
}
+#ifdef CONFIG_HOTPLUG_CPU
+
+/* Because preemptible RCU does not exist, no quieting of tasks. */
+static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
+{
+ spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
/*
/*
* Because preemptable RCU does not exist, it never needs to migrate
- * tasks that were blocked within RCU read-side critical sections.
+ * tasks that were blocked within RCU read-side critical sections, and
+ * such non-existent tasks cannot possibly have been blocking the current
+ * grace period.
*/
-static void rcu_preempt_offline_tasks(struct rcu_state *rsp,
- struct rcu_node *rnp,
- struct rcu_data *rdp)
+static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
+ struct rcu_node *rnp,
+ struct rcu_data *rdp)
{
+ return 0;
}
/*
EXPORT_SYMBOL_GPL(call_rcu);
/*
+ * Wait for an rcu-preempt grace period, but make it happen quickly.
+ * But because preemptable RCU does not exist, map to rcu-sched.
+ */
+void synchronize_rcu_expedited(void)
+{
+ synchronize_sched_expedited();
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Because preemptable RCU does not exist, there is never any need to
+ * report on tasks preempted in RCU read-side critical sections during
+ * expedited RCU grace periods.
+ */
+static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+ return;
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
+/*
* Because preemptable RCU does not exist, it never has any work to do.
*/
static int rcu_preempt_pending(int cpu)
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff