/*
- * Read-Copy Update mechanism for mutual exclusion (tree-based version)
+ * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition
* Internal non-public definitions that provide either classic
- * or preemptable semantics.
+ * or preemptible semantics.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
- * Copyright IBM Corporation, 2009
+ * Copyright (c) 2010 Linaro
*
* Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*/
+#include <linux/kthread.h>
+#include <linux/module.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+
+/* Global control variables for rcupdate callback mechanism. */
+struct rcu_ctrlblk {
+ struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
+ struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
+ struct rcu_head **curtail; /* ->next pointer of last CB. */
+ RCU_TRACE(long qlen); /* Number of pending CBs. */
+ RCU_TRACE(char *name); /* Name of RCU type. */
+};
+
+/* Definition for rcupdate control block. */
+static struct rcu_ctrlblk rcu_sched_ctrlblk = {
+ .donetail = &rcu_sched_ctrlblk.rcucblist,
+ .curtail = &rcu_sched_ctrlblk.rcucblist,
+ RCU_TRACE(.name = "rcu_sched")
+};
+
+static struct rcu_ctrlblk rcu_bh_ctrlblk = {
+ .donetail = &rcu_bh_ctrlblk.rcucblist,
+ .curtail = &rcu_bh_ctrlblk.rcucblist,
+ RCU_TRACE(.name = "rcu_bh")
+};
+
#ifdef CONFIG_DEBUG_LOCK_ALLOC
+int rcu_scheduler_active __read_mostly;
+EXPORT_SYMBOL_GPL(rcu_scheduler_active);
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+#ifdef CONFIG_TINY_PREEMPT_RCU
+
+#include <linux/delay.h>
+
+/* Global control variables for preemptible RCU. */
+struct rcu_preempt_ctrlblk {
+ struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */
+ struct rcu_head **nexttail;
+ /* Tasks blocked in a preemptible RCU */
+ /* read-side critical section while an */
+ /* preemptible-RCU grace period is in */
+ /* progress must wait for a later grace */
+ /* period. This pointer points to the */
+ /* ->next pointer of the last task that */
+ /* must wait for a later grace period, or */
+ /* to &->rcb.rcucblist if there is no */
+ /* such task. */
+ struct list_head blkd_tasks;
+ /* Tasks blocked in RCU read-side critical */
+ /* section. Tasks are placed at the head */
+ /* of this list and age towards the tail. */
+ struct list_head *gp_tasks;
+ /* Pointer to the first task blocking the */
+ /* current grace period, or NULL if there */
+ /* is no such task. */
+ struct list_head *exp_tasks;
+ /* Pointer to first task blocking the */
+ /* current expedited grace period, or NULL */
+ /* if there is no such task. If there */
+ /* is no current expedited grace period, */
+ /* then there cannot be any such task. */
+#ifdef CONFIG_RCU_BOOST
+ struct list_head *boost_tasks;
+ /* Pointer to first task that needs to be */
+ /* priority-boosted, or NULL if no priority */
+ /* boosting is needed. If there is no */
+ /* current or expedited grace period, there */
+ /* can be no such task. */
+#endif /* #ifdef CONFIG_RCU_BOOST */
+ u8 gpnum; /* Current grace period. */
+ u8 gpcpu; /* Last grace period blocked by the CPU. */
+ u8 completed; /* Last grace period completed. */
+ /* If all three are equal, RCU is idle. */
+#ifdef CONFIG_RCU_BOOST
+ unsigned long boost_time; /* When to start boosting (jiffies) */
+#endif /* #ifdef CONFIG_RCU_BOOST */
+#ifdef CONFIG_RCU_TRACE
+ unsigned long n_grace_periods;
+#ifdef CONFIG_RCU_BOOST
+ unsigned long n_tasks_boosted;
+ /* Total number of tasks boosted. */
+ unsigned long n_exp_boosts;
+ /* Number of tasks boosted for expedited GP. */
+ unsigned long n_normal_boosts;
+ /* Number of tasks boosted for normal GP. */
+ unsigned long n_balk_blkd_tasks;
+ /* Refused to boost: no blocked tasks. */
+ unsigned long n_balk_exp_gp_tasks;
+ /* Refused to boost: nothing blocking GP. */
+ unsigned long n_balk_boost_tasks;
+ /* Refused to boost: already boosting. */
+ unsigned long n_balk_notyet;
+ /* Refused to boost: not yet time. */
+ unsigned long n_balk_nos;
+ /* Refused to boost: not sure why, though. */
+ /* This can happen due to race conditions. */
+#endif /* #ifdef CONFIG_RCU_BOOST */
+#endif /* #ifdef CONFIG_RCU_TRACE */
+};
+
+static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
+ .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist,
+ .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist,
+ .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist,
+ .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks),
+ RCU_TRACE(.rcb.name = "rcu_preempt")
+};
+
+static void rcu_read_unlock_special(struct task_struct *t);
+static int rcu_preempted_readers_exp(void);
+static void rcu_report_exp_done(void);
+
+/*
+ * Return true if the CPU has not yet responded to the current grace period.
+ */
+static int rcu_cpu_blocking_cur_gp(void)
+{
+ return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum;
+}
+
+/*
+ * Check for a running RCU reader. Because there is only one CPU,
+ * there can be but one running RCU reader at a time. ;-)
+ *
+ * Returns zero if there are no running readers. Returns a positive
+ * number if there is at least one reader within its RCU read-side
+ * critical section. Returns a negative number if an outermost reader
+ * is in the midst of exiting from its RCU read-side critical section
+ *
+ * Returns zero if there are no running readers. Returns a positive
+ * number if there is at least one reader within its RCU read-side
+ * critical section. Returns a negative number if an outermost reader
+ * is in the midst of exiting from its RCU read-side critical section.
+ */
+static int rcu_preempt_running_reader(void)
+{
+ return current->rcu_read_lock_nesting;
+}
+
+/*
+ * Check for preempted RCU readers blocking any grace period.
+ * If the caller needs a reliable answer, it must disable hard irqs.
+ */
+static int rcu_preempt_blocked_readers_any(void)
+{
+ return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks);
+}
+
+/*
+ * Check for preempted RCU readers blocking the current grace period.
+ * If the caller needs a reliable answer, it must disable hard irqs.
+ */
+static int rcu_preempt_blocked_readers_cgp(void)
+{
+ return rcu_preempt_ctrlblk.gp_tasks != NULL;
+}
+
+/*
+ * Return true if another preemptible-RCU grace period is needed.
+ */
+static int rcu_preempt_needs_another_gp(void)
+{
+ return *rcu_preempt_ctrlblk.rcb.curtail != NULL;
+}
+
+/*
+ * Return true if a preemptible-RCU grace period is in progress.
+ * The caller must disable hardirqs.
+ */
+static int rcu_preempt_gp_in_progress(void)
+{
+ return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum;
+}
+
+/*
+ * Advance a ->blkd_tasks-list pointer to the next entry, instead
+ * returning NULL if at the end of the list.
+ */
+static struct list_head *rcu_next_node_entry(struct task_struct *t)
+{
+ struct list_head *np;
+
+ np = t->rcu_node_entry.next;
+ if (np == &rcu_preempt_ctrlblk.blkd_tasks)
+ np = NULL;
+ return np;
+}
+
+#ifdef CONFIG_RCU_TRACE
+
+#ifdef CONFIG_RCU_BOOST
+static void rcu_initiate_boost_trace(void);
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+/*
+ * Dump additional statistice for TINY_PREEMPT_RCU.
+ */
+static void show_tiny_preempt_stats(struct seq_file *m)
+{
+ seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n",
+ rcu_preempt_ctrlblk.rcb.qlen,
+ rcu_preempt_ctrlblk.n_grace_periods,
+ rcu_preempt_ctrlblk.gpnum,
+ rcu_preempt_ctrlblk.gpcpu,
+ rcu_preempt_ctrlblk.completed,
+ "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)],
+ "N."[!rcu_preempt_ctrlblk.gp_tasks],
+ "E."[!rcu_preempt_ctrlblk.exp_tasks]);
+#ifdef CONFIG_RCU_BOOST
+ seq_printf(m, "%sttb=%c ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n",
+ " ",
+ "B."[!rcu_preempt_ctrlblk.boost_tasks],
+ rcu_preempt_ctrlblk.n_tasks_boosted,
+ rcu_preempt_ctrlblk.n_exp_boosts,
+ rcu_preempt_ctrlblk.n_normal_boosts,
+ (int)(jiffies & 0xffff),
+ (int)(rcu_preempt_ctrlblk.boost_time & 0xffff));
+ seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu ny=%lu nos=%lu\n",
+ " balk",
+ rcu_preempt_ctrlblk.n_balk_blkd_tasks,
+ rcu_preempt_ctrlblk.n_balk_exp_gp_tasks,
+ rcu_preempt_ctrlblk.n_balk_boost_tasks,
+ rcu_preempt_ctrlblk.n_balk_notyet,
+ rcu_preempt_ctrlblk.n_balk_nos);
+#endif /* #ifdef CONFIG_RCU_BOOST */
+}
+
+#endif /* #ifdef CONFIG_RCU_TRACE */
+
+#ifdef CONFIG_RCU_BOOST
+
+#include "rtmutex_common.h"
+
+#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
+
+/* Controls for rcu_kthread() kthread. */
+static struct task_struct *rcu_kthread_task;
+static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
+static unsigned long have_rcu_kthread_work;
+
+/*
+ * Carry out RCU priority boosting on the task indicated by ->boost_tasks,
+ * and advance ->boost_tasks to the next task in the ->blkd_tasks list.
+ */
+static int rcu_boost(void)
+{
+ unsigned long flags;
+ struct rt_mutex mtx;
+ struct task_struct *t;
+ struct list_head *tb;
+
+ if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
+ rcu_preempt_ctrlblk.exp_tasks == NULL)
+ return 0; /* Nothing to boost. */
+
+ raw_local_irq_save(flags);
+
+ /*
+ * Recheck with irqs disabled: all tasks in need of boosting
+ * might exit their RCU read-side critical sections on their own
+ * if we are preempted just before disabling irqs.
+ */
+ if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
+ rcu_preempt_ctrlblk.exp_tasks == NULL) {
+ raw_local_irq_restore(flags);
+ return 0;
+ }
+
+ /*
+ * Preferentially boost tasks blocking expedited grace periods.
+ * This cannot starve the normal grace periods because a second
+ * expedited grace period must boost all blocked tasks, including
+ * those blocking the pre-existing normal grace period.
+ */
+ if (rcu_preempt_ctrlblk.exp_tasks != NULL) {
+ tb = rcu_preempt_ctrlblk.exp_tasks;
+ RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++);
+ } else {
+ tb = rcu_preempt_ctrlblk.boost_tasks;
+ RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++);
+ }
+ RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++);
+
+ /*
+ * We boost task t by manufacturing an rt_mutex that appears to
+ * be held by task t. We leave a pointer to that rt_mutex where
+ * task t can find it, and task t will release the mutex when it
+ * exits its outermost RCU read-side critical section. Then
+ * simply acquiring this artificial rt_mutex will boost task
+ * t's priority. (Thanks to tglx for suggesting this approach!)
+ */
+ t = container_of(tb, struct task_struct, rcu_node_entry);
+ rt_mutex_init_proxy_locked(&mtx, t);
+ t->rcu_boost_mutex = &mtx;
+ raw_local_irq_restore(flags);
+ rt_mutex_lock(&mtx);
+ rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
+
+ return ACCESS_ONCE(rcu_preempt_ctrlblk.boost_tasks) != NULL ||
+ ACCESS_ONCE(rcu_preempt_ctrlblk.exp_tasks) != NULL;
+}
+
+/*
+ * Check to see if it is now time to start boosting RCU readers blocking
+ * the current grace period, and, if so, tell the rcu_kthread_task to
+ * start boosting them. If there is an expedited boost in progress,
+ * we wait for it to complete.
+ *
+ * If there are no blocked readers blocking the current grace period,
+ * return 0 to let the caller know, otherwise return 1. Note that this
+ * return value is independent of whether or not boosting was done.
+ */
+static int rcu_initiate_boost(void)
+{
+ if (!rcu_preempt_blocked_readers_cgp() &&
+ rcu_preempt_ctrlblk.exp_tasks == NULL) {
+ RCU_TRACE(rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++);
+ return 0;
+ }
+ if (rcu_preempt_ctrlblk.exp_tasks != NULL ||
+ (rcu_preempt_ctrlblk.gp_tasks != NULL &&
+ rcu_preempt_ctrlblk.boost_tasks == NULL &&
+ ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))) {
+ if (rcu_preempt_ctrlblk.exp_tasks == NULL)
+ rcu_preempt_ctrlblk.boost_tasks =
+ rcu_preempt_ctrlblk.gp_tasks;
+ invoke_rcu_callbacks();
+ } else
+ RCU_TRACE(rcu_initiate_boost_trace());
+ return 1;
+}
+
+#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
+
+/*
+ * Do priority-boost accounting for the start of a new grace period.
+ */
+static void rcu_preempt_boost_start_gp(void)
+{
+ rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
+}
+
+#else /* #ifdef CONFIG_RCU_BOOST */
+
+/*
+ * If there is no RCU priority boosting, we don't initiate boosting,
+ * but we do indicate whether there are blocked readers blocking the
+ * current grace period.
+ */
+static int rcu_initiate_boost(void)
+{
+ return rcu_preempt_blocked_readers_cgp();
+}
+
+/*
+ * If there is no RCU priority boosting, nothing to do at grace-period start.
+ */
+static void rcu_preempt_boost_start_gp(void)
+{
+}
+
+#endif /* else #ifdef CONFIG_RCU_BOOST */
+
+/*
+ * Record a preemptible-RCU quiescent state for the specified CPU. Note
+ * that this just means that the task currently running on the CPU is
+ * in a quiescent state. There might be any number of tasks blocked
+ * while in an RCU read-side critical section.
+ *
+ * Unlike the other rcu_*_qs() functions, callers to this function
+ * must disable irqs in order to protect the assignment to
+ * ->rcu_read_unlock_special.
+ *
+ * Because this is a single-CPU implementation, the only way a grace
+ * period can end is if the CPU is in a quiescent state. The reason is
+ * that a blocked preemptible-RCU reader can exit its critical section
+ * only if the CPU is running it at the time. Therefore, when the
+ * last task blocking the current grace period exits its RCU read-side
+ * critical section, neither the CPU nor blocked tasks will be stopping
+ * the current grace period. (In contrast, SMP implementations
+ * might have CPUs running in RCU read-side critical sections that
+ * block later grace periods -- but this is not possible given only
+ * one CPU.)
+ */
+static void rcu_preempt_cpu_qs(void)
+{
+ /* Record both CPU and task as having responded to current GP. */
+ rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum;
+ current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
+
+ /* If there is no GP then there is nothing more to do. */
+ if (!rcu_preempt_gp_in_progress())
+ return;
+ /*
+ * Check up on boosting. If there are readers blocking the
+ * current grace period, leave.
+ */
+ if (rcu_initiate_boost())
+ return;
+
+ /* Advance callbacks. */
+ rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum;
+ rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail;
+ rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail;
+
+ /* If there are no blocked readers, next GP is done instantly. */
+ if (!rcu_preempt_blocked_readers_any())
+ rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail;
+
+ /* If there are done callbacks, cause them to be invoked. */
+ if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
+ invoke_rcu_callbacks();
+}
+
+/*
+ * Start a new RCU grace period if warranted. Hard irqs must be disabled.
+ */
+static void rcu_preempt_start_gp(void)
+{
+ if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) {
+
+ /* Official start of GP. */
+ rcu_preempt_ctrlblk.gpnum++;
+ RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++);
+
+ /* Any blocked RCU readers block new GP. */
+ if (rcu_preempt_blocked_readers_any())
+ rcu_preempt_ctrlblk.gp_tasks =
+ rcu_preempt_ctrlblk.blkd_tasks.next;
+
+ /* Set up for RCU priority boosting. */
+ rcu_preempt_boost_start_gp();
+
+ /* If there is no running reader, CPU is done with GP. */
+ if (!rcu_preempt_running_reader())
+ rcu_preempt_cpu_qs();
+ }
+}
+
+/*
+ * We have entered the scheduler, and the current task might soon be
+ * context-switched away from. If this task is in an RCU read-side
+ * critical section, we will no longer be able to rely on the CPU to
+ * record that fact, so we enqueue the task on the blkd_tasks list.
+ * If the task started after the current grace period began, as recorded
+ * by ->gpcpu, we enqueue at the beginning of the list. Otherwise
+ * before the element referenced by ->gp_tasks (or at the tail if
+ * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element.
+ * The task will dequeue itself when it exits the outermost enclosing
+ * RCU read-side critical section. Therefore, the current grace period
+ * cannot be permitted to complete until the ->gp_tasks pointer becomes
+ * NULL.
+ *
+ * Caller must disable preemption.
+ */
+void rcu_preempt_note_context_switch(void)
+{
+ struct task_struct *t = current;
+ unsigned long flags;
+ local_irq_save(flags); /* must exclude scheduler_tick(). */
+ if (rcu_preempt_running_reader() > 0 &&
+ (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
+
+ /* Possibly blocking in an RCU read-side critical section. */
+ t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
+
+ /*
+ * If this CPU has already checked in, then this task
+ * will hold up the next grace period rather than the
+ * current grace period. Queue the task accordingly.
+ * If the task is queued for the current grace period
+ * (i.e., this CPU has not yet passed through a quiescent
+ * state for the current grace period), then as long
+ * as that task remains queued, the current grace period
+ * cannot end.
+ */
+ list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
+ if (rcu_cpu_blocking_cur_gp())
+ rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
+ } else if (rcu_preempt_running_reader() < 0 &&
+ t->rcu_read_unlock_special) {
+ /*
+ * Complete exit from RCU read-side critical section on
+ * behalf of preempted instance of __rcu_read_unlock().
+ */
+ rcu_read_unlock_special(t);
+ }
+
+ /*
+ * Either we were not in an RCU read-side critical section to
+ * begin with, or we have now recorded that critical section
+ * globally. Either way, we can now note a quiescent state
+ * for this CPU. Again, if we were in an RCU read-side critical
+ * section, and if that critical section was blocking the current
+ * grace period, then the fact that the task has been enqueued
+ * means that current grace period continues to be blocked.
+ */
+ rcu_preempt_cpu_qs();
+ local_irq_restore(flags);
+}
+
+/*
+ * Tiny-preemptible RCU implementation for rcu_read_lock().
+ * Just increment ->rcu_read_lock_nesting, shared state will be updated
+ * if we block.
+ */
+void __rcu_read_lock(void)
+{
+ current->rcu_read_lock_nesting++;
+ barrier(); /* needed if we ever invoke rcu_read_lock in rcutiny.c */
+}
+EXPORT_SYMBOL_GPL(__rcu_read_lock);
+
+/*
+ * 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 noinline void rcu_read_unlock_special(struct task_struct *t)
+{
+ int empty;
+ int empty_exp;
+ unsigned long flags;
+ struct list_head *np;
+#ifdef CONFIG_RCU_BOOST
+ struct rt_mutex *rbmp = NULL;
+#endif /* #ifdef CONFIG_RCU_BOOST */
+ int special;
+
+ /*
+ * NMI handlers cannot block and cannot safely manipulate state.
+ * They therefore cannot possibly be special, so just leave.
+ */
+ if (in_nmi())
+ return;
+
+ local_irq_save(flags);
+
+ /*
+ * If RCU core is waiting for this CPU to exit critical section,
+ * let it know that we have done so.
+ */
+ special = t->rcu_read_unlock_special;
+ if (special & RCU_READ_UNLOCK_NEED_QS)
+ rcu_preempt_cpu_qs();
+
+ /* Hardware IRQ handlers cannot block. */
+ if (in_irq() || in_serving_softirq()) {
+ local_irq_restore(flags);
+ return;
+ }
+
+ /* Clean up if blocked during RCU read-side critical section. */
+ if (special & RCU_READ_UNLOCK_BLOCKED) {
+ t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
+
+ /*
+ * Remove this task from the ->blkd_tasks list and adjust
+ * any pointers that might have been referencing it.
+ */
+ empty = !rcu_preempt_blocked_readers_cgp();
+ empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL;
+ np = rcu_next_node_entry(t);
+ list_del_init(&t->rcu_node_entry);
+ if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks)
+ rcu_preempt_ctrlblk.gp_tasks = np;
+ if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks)
+ rcu_preempt_ctrlblk.exp_tasks = np;
+#ifdef CONFIG_RCU_BOOST
+ if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks)
+ rcu_preempt_ctrlblk.boost_tasks = np;
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+ /*
+ * If this was the last task on the current list, and if
+ * we aren't waiting on the CPU, report the quiescent state
+ * and start a new grace period if needed.
+ */
+ if (!empty && !rcu_preempt_blocked_readers_cgp()) {
+ rcu_preempt_cpu_qs();
+ rcu_preempt_start_gp();
+ }
+
+ /*
+ * If this was the last task on the expedited lists,
+ * then we need wake up the waiting task.
+ */
+ if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL)
+ rcu_report_exp_done();
+ }
+#ifdef CONFIG_RCU_BOOST
+ /* Unboost self if was boosted. */
+ if (t->rcu_boost_mutex != NULL) {
+ rbmp = t->rcu_boost_mutex;
+ t->rcu_boost_mutex = NULL;
+ rt_mutex_unlock(rbmp);
+ }
+#endif /* #ifdef CONFIG_RCU_BOOST */
+ local_irq_restore(flags);
+}
+
+/*
+ * Tiny-preemptible RCU implementation for rcu_read_unlock().
+ * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
+ * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
+ * invoke rcu_read_unlock_special() to clean up after a context switch
+ * in an RCU read-side critical section and other special cases.
+ */
+void __rcu_read_unlock(void)
+{
+ struct task_struct *t = current;
+
+ barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */
+ if (t->rcu_read_lock_nesting != 1)
+ --t->rcu_read_lock_nesting;
+ else {
+ t->rcu_read_lock_nesting = INT_MIN;
+ barrier(); /* assign before ->rcu_read_unlock_special load */
+ if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
+ rcu_read_unlock_special(t);
+ barrier(); /* ->rcu_read_unlock_special load before assign */
+ t->rcu_read_lock_nesting = 0;
+ }
+#ifdef CONFIG_PROVE_LOCKING
+ {
+ int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
+
+ WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
+ }
+#endif /* #ifdef CONFIG_PROVE_LOCKING */
+}
+EXPORT_SYMBOL_GPL(__rcu_read_unlock);
+
+/*
+ * Check for a quiescent state from the current CPU. When a task blocks,
+ * the task is recorded in the rcu_preempt_ctrlblk structure, which is
+ * checked elsewhere. This is called from the scheduling-clock interrupt.
+ *
+ * Caller must disable hard irqs.
+ */
+static void rcu_preempt_check_callbacks(void)
+{
+ struct task_struct *t = current;
+
+ if (rcu_preempt_gp_in_progress() &&
+ (!rcu_preempt_running_reader() ||
+ !rcu_cpu_blocking_cur_gp()))
+ rcu_preempt_cpu_qs();
+ if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
+ rcu_preempt_ctrlblk.rcb.donetail)
+ invoke_rcu_callbacks();
+ if (rcu_preempt_gp_in_progress() &&
+ rcu_cpu_blocking_cur_gp() &&
+ rcu_preempt_running_reader() > 0)
+ t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
+}
+
+/*
+ * TINY_PREEMPT_RCU has an extra callback-list tail pointer to
+ * update, so this is invoked from rcu_process_callbacks() to
+ * handle that case. Of course, it is invoked for all flavors of
+ * RCU, but RCU callbacks can appear only on one of the lists, and
+ * neither ->nexttail nor ->donetail can possibly be NULL, so there
+ * is no need for an explicit check.
+ */
+static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
+{
+ if (rcu_preempt_ctrlblk.nexttail == rcp->donetail)
+ rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist;
+}
+
+/*
+ * Process callbacks for preemptible RCU.
+ */
+static void rcu_preempt_process_callbacks(void)
+{
+ __rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
+}
+
+/*
+ * Queue a preemptible -RCU callback for invocation after a grace period.
+ */
+void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
+{
+ unsigned long flags;
+
+ debug_rcu_head_queue(head);
+ head->func = func;
+ head->next = NULL;
+
+ local_irq_save(flags);
+ *rcu_preempt_ctrlblk.nexttail = head;
+ rcu_preempt_ctrlblk.nexttail = &head->next;
+ RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++);
+ rcu_preempt_start_gp(); /* checks to see if GP needed. */
+ local_irq_restore(flags);
+}
+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)
+{
+ rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
+ !lock_is_held(&rcu_lock_map) &&
+ !lock_is_held(&rcu_sched_lock_map),
+ "Illegal synchronize_rcu() in RCU read-side critical section");
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ if (!rcu_scheduler_active)
+ return;
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+ WARN_ON_ONCE(rcu_preempt_running_reader());
+ if (!rcu_preempt_blocked_readers_any())
+ return;
+
+ /* Once we get past the fastpath checks, same code as rcu_barrier(). */
+ rcu_barrier();
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu);
+
+static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
+static unsigned 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(void)
+{
+ return rcu_preempt_ctrlblk.exp_tasks != NULL;
+}
+
+/*
+ * 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.
+ */
+static void rcu_report_exp_done(void)
+{
+ wake_up(&sync_rcu_preempt_exp_wq);
+}
+
+/*
+ * Wait for an rcu-preempt grace period, but expedite it. The basic idea
+ * is to rely in the fact that there is but one CPU, and that it is
+ * illegal for a task to invoke synchronize_rcu_expedited() while in a
+ * preemptible-RCU read-side critical section. Therefore, any such
+ * critical sections must correspond to blocked tasks, which must therefore
+ * be on the ->blkd_tasks list. So just record the current head of the
+ * list in the ->exp_tasks pointer, and wait for all tasks including and
+ * after the task pointed to by ->exp_tasks to drain.
+ */
+void synchronize_rcu_expedited(void)
+{
+ unsigned long flags;
+ struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk;
+ unsigned long snap;
+
+ barrier(); /* ensure prior action seen before grace period. */
+
+ WARN_ON_ONCE(rcu_preempt_running_reader());
+
+ /*
+ * Acquire lock so that there is only one preemptible RCU grace
+ * period in flight. Of course, if someone does the expedited
+ * grace period for us while we are acquiring the lock, just leave.
+ */
+ snap = sync_rcu_preempt_exp_count + 1;
+ mutex_lock(&sync_rcu_preempt_exp_mutex);
+ if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count))
+ goto unlock_mb_ret; /* Others did our work for us. */
+
+ local_irq_save(flags);
+
+ /*
+ * All RCU readers have to already be on blkd_tasks because
+ * we cannot legally be executing in an RCU read-side critical
+ * section.
+ */
+
+ /* Snapshot current head of ->blkd_tasks list. */
+ rpcp->exp_tasks = rpcp->blkd_tasks.next;
+ if (rpcp->exp_tasks == &rpcp->blkd_tasks)
+ rpcp->exp_tasks = NULL;
+
+ /* Wait for tail of ->blkd_tasks list to drain. */
+ if (!rcu_preempted_readers_exp())
+ local_irq_restore(flags);
+ else {
+ rcu_initiate_boost();
+ local_irq_restore(flags);
+ wait_event(sync_rcu_preempt_exp_wq,
+ !rcu_preempted_readers_exp());
+ }
+
+ /* Clean up and exit. */
+ barrier(); /* ensure expedited GP seen before counter increment. */
+ sync_rcu_preempt_exp_count++;
+unlock_mb_ret:
+ mutex_unlock(&sync_rcu_preempt_exp_mutex);
+ barrier(); /* ensure subsequent action seen after grace period. */
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+/*
+ * Does preemptible RCU need the CPU to stay out of dynticks mode?
+ */
+int rcu_preempt_needs_cpu(void)
+{
+ if (!rcu_preempt_running_reader())
+ rcu_preempt_cpu_qs();
+ return rcu_preempt_ctrlblk.rcb.rcucblist != NULL;
+}
+
+/*
+ * Check for a task exiting while in a preemptible -RCU read-side
+ * critical section, clean up if so. No need to issue warnings,
+ * as debug_check_no_locks_held() already does this if lockdep
+ * is enabled.
+ */
+void exit_rcu(void)
+{
+ struct task_struct *t = current;
+
+ if (t->rcu_read_lock_nesting == 0)
+ return;
+ t->rcu_read_lock_nesting = 1;
+ __rcu_read_unlock();
+}
+
+#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
+
+#ifdef CONFIG_RCU_TRACE
+
+/*
+ * Because preemptible RCU does not exist, it is not necessary to
+ * dump out its statistics.
+ */
+static void show_tiny_preempt_stats(struct seq_file *m)
+{
+}
+
+#endif /* #ifdef CONFIG_RCU_TRACE */
+
+/*
+ * Because preemptible RCU does not exist, it never has any callbacks
+ * to check.
+ */
+static void rcu_preempt_check_callbacks(void)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, it never has any callbacks
+ * to remove.
+ */
+static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, it never has any callbacks
+ * to process.
+ */
+static void rcu_preempt_process_callbacks(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */
+
+#ifdef CONFIG_RCU_BOOST
+
+/*
+ * Wake up rcu_kthread() to process callbacks now eligible for invocation
+ * or to boost readers.
+ */
+static void invoke_rcu_callbacks(void)
+{
+ have_rcu_kthread_work = 1;
+ if (rcu_kthread_task != NULL)
+ wake_up(&rcu_kthread_wq);
+}
+
+#ifdef CONFIG_RCU_TRACE
+
+/*
+ * Is the current CPU running the RCU-callbacks kthread?
+ * Caller must have preemption disabled.
+ */
+static bool rcu_is_callbacks_kthread(void)
+{
+ return rcu_kthread_task == current;
+}
+
+#endif /* #ifdef CONFIG_RCU_TRACE */
+
+/*
+ * This kthread invokes RCU callbacks whose grace periods have
+ * elapsed. It is awakened as needed, and takes the place of the
+ * RCU_SOFTIRQ that is used for this purpose when boosting is disabled.
+ * This is a kthread, but it is never stopped, at least not until
+ * the system goes down.
+ */
+static int rcu_kthread(void *arg)
+{
+ unsigned long work;
+ unsigned long morework;
+ unsigned long flags;
+
+ for (;;) {
+ wait_event_interruptible(rcu_kthread_wq,
+ have_rcu_kthread_work != 0);
+ morework = rcu_boost();
+ local_irq_save(flags);
+ work = have_rcu_kthread_work;
+ have_rcu_kthread_work = morework;
+ local_irq_restore(flags);
+ if (work)
+ rcu_process_callbacks(NULL);
+ schedule_timeout_interruptible(1); /* Leave CPU for others. */
+ }
+
+ return 0; /* Not reached, but needed to shut gcc up. */
+}
+
+/*
+ * Spawn the kthread that invokes RCU callbacks.
+ */
+static int __init rcu_spawn_kthreads(void)
+{
+ struct sched_param sp;
+
+ rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");
+ sp.sched_priority = RCU_BOOST_PRIO;
+ sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);
+ return 0;
+}
+early_initcall(rcu_spawn_kthreads);
+
+#else /* #ifdef CONFIG_RCU_BOOST */
+
+/* Hold off callback invocation until early_initcall() time. */
+static int rcu_scheduler_fully_active __read_mostly;
+
+/*
+ * Start up softirq processing of callbacks.
+ */
+void invoke_rcu_callbacks(void)
+{
+ if (rcu_scheduler_fully_active)
+ raise_softirq(RCU_SOFTIRQ);
+}
+
+#ifdef CONFIG_RCU_TRACE
+
+/*
+ * There is no callback kthread, so this thread is never it.
+ */
+static bool rcu_is_callbacks_kthread(void)
+{
+ return false;
+}
+
+#endif /* #ifdef CONFIG_RCU_TRACE */
+
+static int __init rcu_scheduler_really_started(void)
+{
+ rcu_scheduler_fully_active = 1;
+ open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+ raise_softirq(RCU_SOFTIRQ); /* Invoke any callbacks from early boot. */
+ return 0;
+}
+early_initcall(rcu_scheduler_really_started);
+
+#endif /* #else #ifdef CONFIG_RCU_BOOST */
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
#include <linux/kernel_stat.h>
/*
* During boot, we forgive RCU lockdep issues. After this function is
* invoked, we start taking RCU lockdep issues seriously.
*/
-void rcu_scheduler_starting(void)
+void __init rcu_scheduler_starting(void)
{
WARN_ON(nr_context_switches() > 0);
rcu_scheduler_active = 1;
}
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+#ifdef CONFIG_RCU_TRACE
+
+#ifdef CONFIG_RCU_BOOST
+
+static void rcu_initiate_boost_trace(void)
+{
+ if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks))
+ rcu_preempt_ctrlblk.n_balk_blkd_tasks++;
+ else if (rcu_preempt_ctrlblk.gp_tasks == NULL &&
+ rcu_preempt_ctrlblk.exp_tasks == NULL)
+ rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++;
+ else if (rcu_preempt_ctrlblk.boost_tasks != NULL)
+ rcu_preempt_ctrlblk.n_balk_boost_tasks++;
+ else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))
+ rcu_preempt_ctrlblk.n_balk_notyet++;
+ else
+ rcu_preempt_ctrlblk.n_balk_nos++;
+}
+
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
+{
+ unsigned long flags;
+
+ raw_local_irq_save(flags);
+ rcp->qlen -= n;
+ raw_local_irq_restore(flags);
+}
+
+/*
+ * Dump statistics for TINY_RCU, such as they are.
+ */
+static int show_tiny_stats(struct seq_file *m, void *unused)
+{
+ show_tiny_preempt_stats(m);
+ seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
+ seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
+ return 0;
+}
+
+static int show_tiny_stats_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, show_tiny_stats, NULL);
+}
+
+static const struct file_operations show_tiny_stats_fops = {
+ .owner = THIS_MODULE,
+ .open = show_tiny_stats_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+static struct dentry *rcudir;
+
+static int __init rcutiny_trace_init(void)
+{
+ struct dentry *retval;
+
+ rcudir = debugfs_create_dir("rcu", NULL);
+ if (!rcudir)
+ goto free_out;
+ retval = debugfs_create_file("rcudata", 0444, rcudir,
+ NULL, &show_tiny_stats_fops);
+ if (!retval)
+ goto free_out;
+ return 0;
+free_out:
+ debugfs_remove_recursive(rcudir);
+ return 1;
+}
+
+static void __exit rcutiny_trace_cleanup(void)
+{
+ debugfs_remove_recursive(rcudir);
+}
+
+module_init(rcutiny_trace_init);
+module_exit(rcutiny_trace_cleanup);
+
+MODULE_AUTHOR("Paul E. McKenney");
+MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
+MODULE_LICENSE("GPL");
+
+#endif /* #ifdef CONFIG_RCU_TRACE */
projects / linux-flexiantxendom0-3.2.10.git / blobdiff