Update Linux to v5.10.109
Sourced from [1]
[1] https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.10.109.tar.xz
Change-Id: I19bca9fc6762d4e63bcf3e4cba88bbe560d9c76c
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
new file mode 100644
index 0000000..7c05c5a
--- /dev/null
+++ b/kernel/rcu/tasks.h
@@ -0,0 +1,1249 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Task-based RCU implementations.
+ *
+ * Copyright (C) 2020 Paul E. McKenney
+ */
+
+#ifdef CONFIG_TASKS_RCU_GENERIC
+
+////////////////////////////////////////////////////////////////////////
+//
+// Generic data structures.
+
+struct rcu_tasks;
+typedef void (*rcu_tasks_gp_func_t)(struct rcu_tasks *rtp);
+typedef void (*pregp_func_t)(void);
+typedef void (*pertask_func_t)(struct task_struct *t, struct list_head *hop);
+typedef void (*postscan_func_t)(struct list_head *hop);
+typedef void (*holdouts_func_t)(struct list_head *hop, bool ndrpt, bool *frptp);
+typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
+
+/**
+ * Definition for a Tasks-RCU-like mechanism.
+ * @cbs_head: Head of callback list.
+ * @cbs_tail: Tail pointer for callback list.
+ * @cbs_wq: Wait queue allowning new callback to get kthread's attention.
+ * @cbs_lock: Lock protecting callback list.
+ * @kthread_ptr: This flavor's grace-period/callback-invocation kthread.
+ * @gp_func: This flavor's grace-period-wait function.
+ * @gp_state: Grace period's most recent state transition (debugging).
+ * @gp_sleep: Per-grace-period sleep to prevent CPU-bound looping.
+ * @init_fract: Initial backoff sleep interval.
+ * @gp_jiffies: Time of last @gp_state transition.
+ * @gp_start: Most recent grace-period start in jiffies.
+ * @n_gps: Number of grace periods completed since boot.
+ * @n_ipis: Number of IPIs sent to encourage grace periods to end.
+ * @n_ipis_fails: Number of IPI-send failures.
+ * @pregp_func: This flavor's pre-grace-period function (optional).
+ * @pertask_func: This flavor's per-task scan function (optional).
+ * @postscan_func: This flavor's post-task scan function (optional).
+ * @holdout_func: This flavor's holdout-list scan function (optional).
+ * @postgp_func: This flavor's post-grace-period function (optional).
+ * @call_func: This flavor's call_rcu()-equivalent function.
+ * @name: This flavor's textual name.
+ * @kname: This flavor's kthread name.
+ */
+struct rcu_tasks {
+ struct rcu_head *cbs_head;
+ struct rcu_head **cbs_tail;
+ struct wait_queue_head cbs_wq;
+ raw_spinlock_t cbs_lock;
+ int gp_state;
+ int gp_sleep;
+ int init_fract;
+ unsigned long gp_jiffies;
+ unsigned long gp_start;
+ unsigned long n_gps;
+ unsigned long n_ipis;
+ unsigned long n_ipis_fails;
+ struct task_struct *kthread_ptr;
+ rcu_tasks_gp_func_t gp_func;
+ pregp_func_t pregp_func;
+ pertask_func_t pertask_func;
+ postscan_func_t postscan_func;
+ holdouts_func_t holdouts_func;
+ postgp_func_t postgp_func;
+ call_rcu_func_t call_func;
+ char *name;
+ char *kname;
+};
+
+#define DEFINE_RCU_TASKS(rt_name, gp, call, n) \
+static struct rcu_tasks rt_name = \
+{ \
+ .cbs_tail = &rt_name.cbs_head, \
+ .cbs_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rt_name.cbs_wq), \
+ .cbs_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_lock), \
+ .gp_func = gp, \
+ .call_func = call, \
+ .name = n, \
+ .kname = #rt_name, \
+}
+
+/* Track exiting tasks in order to allow them to be waited for. */
+DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
+
+/* Avoid IPIing CPUs early in the grace period. */
+#define RCU_TASK_IPI_DELAY (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) ? HZ / 2 : 0)
+static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY;
+module_param(rcu_task_ipi_delay, int, 0644);
+
+/* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */
+#define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10)
+static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
+module_param(rcu_task_stall_timeout, int, 0644);
+
+/* RCU tasks grace-period state for debugging. */
+#define RTGS_INIT 0
+#define RTGS_WAIT_WAIT_CBS 1
+#define RTGS_WAIT_GP 2
+#define RTGS_PRE_WAIT_GP 3
+#define RTGS_SCAN_TASKLIST 4
+#define RTGS_POST_SCAN_TASKLIST 5
+#define RTGS_WAIT_SCAN_HOLDOUTS 6
+#define RTGS_SCAN_HOLDOUTS 7
+#define RTGS_POST_GP 8
+#define RTGS_WAIT_READERS 9
+#define RTGS_INVOKE_CBS 10
+#define RTGS_WAIT_CBS 11
+#ifndef CONFIG_TINY_RCU
+static const char * const rcu_tasks_gp_state_names[] = {
+ "RTGS_INIT",
+ "RTGS_WAIT_WAIT_CBS",
+ "RTGS_WAIT_GP",
+ "RTGS_PRE_WAIT_GP",
+ "RTGS_SCAN_TASKLIST",
+ "RTGS_POST_SCAN_TASKLIST",
+ "RTGS_WAIT_SCAN_HOLDOUTS",
+ "RTGS_SCAN_HOLDOUTS",
+ "RTGS_POST_GP",
+ "RTGS_WAIT_READERS",
+ "RTGS_INVOKE_CBS",
+ "RTGS_WAIT_CBS",
+};
+#endif /* #ifndef CONFIG_TINY_RCU */
+
+////////////////////////////////////////////////////////////////////////
+//
+// Generic code.
+
+/* Record grace-period phase and time. */
+static void set_tasks_gp_state(struct rcu_tasks *rtp, int newstate)
+{
+ rtp->gp_state = newstate;
+ rtp->gp_jiffies = jiffies;
+}
+
+#ifndef CONFIG_TINY_RCU
+/* Return state name. */
+static const char *tasks_gp_state_getname(struct rcu_tasks *rtp)
+{
+ int i = data_race(rtp->gp_state); // Let KCSAN detect update races
+ int j = READ_ONCE(i); // Prevent the compiler from reading twice
+
+ if (j >= ARRAY_SIZE(rcu_tasks_gp_state_names))
+ return "???";
+ return rcu_tasks_gp_state_names[j];
+}
+#endif /* #ifndef CONFIG_TINY_RCU */
+
+// Enqueue a callback for the specified flavor of Tasks RCU.
+static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
+ struct rcu_tasks *rtp)
+{
+ unsigned long flags;
+ bool needwake;
+
+ rhp->next = NULL;
+ rhp->func = func;
+ raw_spin_lock_irqsave(&rtp->cbs_lock, flags);
+ needwake = !rtp->cbs_head;
+ WRITE_ONCE(*rtp->cbs_tail, rhp);
+ rtp->cbs_tail = &rhp->next;
+ raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags);
+ /* We can't create the thread unless interrupts are enabled. */
+ if (needwake && READ_ONCE(rtp->kthread_ptr))
+ wake_up(&rtp->cbs_wq);
+}
+
+// Wait for a grace period for the specified flavor of Tasks RCU.
+static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp)
+{
+ /* Complain if the scheduler has not started. */
+ RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
+ "synchronize_rcu_tasks called too soon");
+
+ /* Wait for the grace period. */
+ wait_rcu_gp(rtp->call_func);
+}
+
+/* RCU-tasks kthread that detects grace periods and invokes callbacks. */
+static int __noreturn rcu_tasks_kthread(void *arg)
+{
+ unsigned long flags;
+ struct rcu_head *list;
+ struct rcu_head *next;
+ struct rcu_tasks *rtp = arg;
+
+ /* Run on housekeeping CPUs by default. Sysadm can move if desired. */
+ housekeeping_affine(current, HK_FLAG_RCU);
+ WRITE_ONCE(rtp->kthread_ptr, current); // Let GPs start!
+
+ /*
+ * Each pass through the following loop makes one check for
+ * newly arrived callbacks, and, if there are some, waits for
+ * one RCU-tasks grace period and then invokes the callbacks.
+ * This loop is terminated by the system going down. ;-)
+ */
+ for (;;) {
+ set_tasks_gp_state(rtp, RTGS_WAIT_CBS);
+
+ /* Pick up any new callbacks. */
+ raw_spin_lock_irqsave(&rtp->cbs_lock, flags);
+ smp_mb__after_spinlock(); // Order updates vs. GP.
+ list = rtp->cbs_head;
+ rtp->cbs_head = NULL;
+ rtp->cbs_tail = &rtp->cbs_head;
+ raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags);
+
+ /* If there were none, wait a bit and start over. */
+ if (!list) {
+ wait_event_interruptible(rtp->cbs_wq,
+ READ_ONCE(rtp->cbs_head));
+ if (!rtp->cbs_head) {
+ WARN_ON(signal_pending(current));
+ set_tasks_gp_state(rtp, RTGS_WAIT_WAIT_CBS);
+ schedule_timeout_idle(HZ/10);
+ }
+ continue;
+ }
+
+ // Wait for one grace period.
+ set_tasks_gp_state(rtp, RTGS_WAIT_GP);
+ rtp->gp_start = jiffies;
+ rtp->gp_func(rtp);
+ rtp->n_gps++;
+
+ /* Invoke the callbacks. */
+ set_tasks_gp_state(rtp, RTGS_INVOKE_CBS);
+ while (list) {
+ next = list->next;
+ local_bh_disable();
+ list->func(list);
+ local_bh_enable();
+ list = next;
+ cond_resched();
+ }
+ /* Paranoid sleep to keep this from entering a tight loop */
+ schedule_timeout_idle(rtp->gp_sleep);
+ }
+}
+
+/* Spawn RCU-tasks grace-period kthread. */
+static void __init rcu_spawn_tasks_kthread_generic(struct rcu_tasks *rtp)
+{
+ struct task_struct *t;
+
+ t = kthread_run(rcu_tasks_kthread, rtp, "%s_kthread", rtp->kname);
+ if (WARN_ONCE(IS_ERR(t), "%s: Could not start %s grace-period kthread, OOM is now expected behavior\n", __func__, rtp->name))
+ return;
+ smp_mb(); /* Ensure others see full kthread. */
+}
+
+#ifndef CONFIG_TINY_RCU
+
+/*
+ * Print any non-default Tasks RCU settings.
+ */
+static void __init rcu_tasks_bootup_oddness(void)
+{
+#if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU)
+ if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT)
+ pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout);
+#endif /* #ifdef CONFIG_TASKS_RCU */
+#ifdef CONFIG_TASKS_RCU
+ pr_info("\tTrampoline variant of Tasks RCU enabled.\n");
+#endif /* #ifdef CONFIG_TASKS_RCU */
+#ifdef CONFIG_TASKS_RUDE_RCU
+ pr_info("\tRude variant of Tasks RCU enabled.\n");
+#endif /* #ifdef CONFIG_TASKS_RUDE_RCU */
+#ifdef CONFIG_TASKS_TRACE_RCU
+ pr_info("\tTracing variant of Tasks RCU enabled.\n");
+#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
+}
+
+#endif /* #ifndef CONFIG_TINY_RCU */
+
+#ifndef CONFIG_TINY_RCU
+/* Dump out rcutorture-relevant state common to all RCU-tasks flavors. */
+static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
+{
+ pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c %s\n",
+ rtp->kname,
+ tasks_gp_state_getname(rtp), data_race(rtp->gp_state),
+ jiffies - data_race(rtp->gp_jiffies),
+ data_race(rtp->n_gps),
+ data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis),
+ ".k"[!!data_race(rtp->kthread_ptr)],
+ ".C"[!!data_race(rtp->cbs_head)],
+ s);
+}
+#endif /* #ifndef CONFIG_TINY_RCU */
+
+static void exit_tasks_rcu_finish_trace(struct task_struct *t);
+
+#if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU)
+
+////////////////////////////////////////////////////////////////////////
+//
+// Shared code between task-list-scanning variants of Tasks RCU.
+
+/* Wait for one RCU-tasks grace period. */
+static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
+{
+ struct task_struct *g, *t;
+ unsigned long lastreport;
+ LIST_HEAD(holdouts);
+ int fract;
+
+ set_tasks_gp_state(rtp, RTGS_PRE_WAIT_GP);
+ rtp->pregp_func();
+
+ /*
+ * There were callbacks, so we need to wait for an RCU-tasks
+ * grace period. Start off by scanning the task list for tasks
+ * that are not already voluntarily blocked. Mark these tasks
+ * and make a list of them in holdouts.
+ */
+ set_tasks_gp_state(rtp, RTGS_SCAN_TASKLIST);
+ rcu_read_lock();
+ for_each_process_thread(g, t)
+ rtp->pertask_func(t, &holdouts);
+ rcu_read_unlock();
+
+ set_tasks_gp_state(rtp, RTGS_POST_SCAN_TASKLIST);
+ rtp->postscan_func(&holdouts);
+
+ /*
+ * Each pass through the following loop scans the list of holdout
+ * tasks, removing any that are no longer holdouts. When the list
+ * is empty, we are done.
+ */
+ lastreport = jiffies;
+
+ // Start off with initial wait and slowly back off to 1 HZ wait.
+ fract = rtp->init_fract;
+ if (fract > HZ)
+ fract = HZ;
+
+ for (;;) {
+ bool firstreport;
+ bool needreport;
+ int rtst;
+
+ if (list_empty(&holdouts))
+ break;
+
+ /* Slowly back off waiting for holdouts */
+ set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS);
+ schedule_timeout_idle(HZ/fract);
+
+ if (fract > 1)
+ fract--;
+
+ rtst = READ_ONCE(rcu_task_stall_timeout);
+ needreport = rtst > 0 && time_after(jiffies, lastreport + rtst);
+ if (needreport)
+ lastreport = jiffies;
+ firstreport = true;
+ WARN_ON(signal_pending(current));
+ set_tasks_gp_state(rtp, RTGS_SCAN_HOLDOUTS);
+ rtp->holdouts_func(&holdouts, needreport, &firstreport);
+ }
+
+ set_tasks_gp_state(rtp, RTGS_POST_GP);
+ rtp->postgp_func(rtp);
+}
+
+#endif /* #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) */
+
+#ifdef CONFIG_TASKS_RCU
+
+////////////////////////////////////////////////////////////////////////
+//
+// Simple variant of RCU whose quiescent states are voluntary context
+// switch, cond_resched_rcu_qs(), user-space execution, and idle.
+// As such, grace periods can take one good long time. There are no
+// read-side primitives similar to rcu_read_lock() and rcu_read_unlock()
+// because this implementation is intended to get the system into a safe
+// state for some of the manipulations involved in tracing and the like.
+// Finally, this implementation does not support high call_rcu_tasks()
+// rates from multiple CPUs. If this is required, per-CPU callback lists
+// will be needed.
+
+/* Pre-grace-period preparation. */
+static void rcu_tasks_pregp_step(void)
+{
+ /*
+ * Wait for all pre-existing t->on_rq and t->nvcsw transitions
+ * to complete. Invoking synchronize_rcu() suffices because all
+ * these transitions occur with interrupts disabled. Without this
+ * synchronize_rcu(), a read-side critical section that started
+ * before the grace period might be incorrectly seen as having
+ * started after the grace period.
+ *
+ * This synchronize_rcu() also dispenses with the need for a
+ * memory barrier on the first store to t->rcu_tasks_holdout,
+ * as it forces the store to happen after the beginning of the
+ * grace period.
+ */
+ synchronize_rcu();
+}
+
+/* Per-task initial processing. */
+static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop)
+{
+ if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) {
+ get_task_struct(t);
+ t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
+ WRITE_ONCE(t->rcu_tasks_holdout, true);
+ list_add(&t->rcu_tasks_holdout_list, hop);
+ }
+}
+
+/* Processing between scanning taskslist and draining the holdout list. */
+static void rcu_tasks_postscan(struct list_head *hop)
+{
+ /*
+ * Wait for tasks that are in the process of exiting. This
+ * does only part of the job, ensuring that all tasks that were
+ * previously exiting reach the point where they have disabled
+ * preemption, allowing the later synchronize_rcu() to finish
+ * the job.
+ */
+ synchronize_srcu(&tasks_rcu_exit_srcu);
+}
+
+/* See if tasks are still holding out, complain if so. */
+static void check_holdout_task(struct task_struct *t,
+ bool needreport, bool *firstreport)
+{
+ int cpu;
+
+ if (!READ_ONCE(t->rcu_tasks_holdout) ||
+ t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
+ !READ_ONCE(t->on_rq) ||
+ (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
+ !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
+ WRITE_ONCE(t->rcu_tasks_holdout, false);
+ list_del_init(&t->rcu_tasks_holdout_list);
+ put_task_struct(t);
+ return;
+ }
+ rcu_request_urgent_qs_task(t);
+ if (!needreport)
+ return;
+ if (*firstreport) {
+ pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
+ *firstreport = false;
+ }
+ cpu = task_cpu(t);
+ pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
+ t, ".I"[is_idle_task(t)],
+ "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
+ t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
+ t->rcu_tasks_idle_cpu, cpu);
+ sched_show_task(t);
+}
+
+/* Scan the holdout lists for tasks no longer holding out. */
+static void check_all_holdout_tasks(struct list_head *hop,
+ bool needreport, bool *firstreport)
+{
+ struct task_struct *t, *t1;
+
+ list_for_each_entry_safe(t, t1, hop, rcu_tasks_holdout_list) {
+ check_holdout_task(t, needreport, firstreport);
+ cond_resched();
+ }
+}
+
+/* Finish off the Tasks-RCU grace period. */
+static void rcu_tasks_postgp(struct rcu_tasks *rtp)
+{
+ /*
+ * Because ->on_rq and ->nvcsw are not guaranteed to have a full
+ * memory barriers prior to them in the schedule() path, memory
+ * reordering on other CPUs could cause their RCU-tasks read-side
+ * critical sections to extend past the end of the grace period.
+ * However, because these ->nvcsw updates are carried out with
+ * interrupts disabled, we can use synchronize_rcu() to force the
+ * needed ordering on all such CPUs.
+ *
+ * This synchronize_rcu() also confines all ->rcu_tasks_holdout
+ * accesses to be within the grace period, avoiding the need for
+ * memory barriers for ->rcu_tasks_holdout accesses.
+ *
+ * In addition, this synchronize_rcu() waits for exiting tasks
+ * to complete their final preempt_disable() region of execution,
+ * cleaning up after the synchronize_srcu() above.
+ */
+ synchronize_rcu();
+}
+
+void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func);
+DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks");
+
+/**
+ * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
+ * @rhp: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. call_rcu_tasks() assumes
+ * that the read-side critical sections end at a voluntary context
+ * switch (not a preemption!), cond_resched_rcu_qs(), entry into idle,
+ * or transition to usermode execution. As such, there are no read-side
+ * primitives analogous to rcu_read_lock() and rcu_read_unlock() because
+ * this primitive is intended to determine that all tasks have passed
+ * through a safe state, not so much for data-strcuture synchronization.
+ *
+ * See the description of call_rcu() for more detailed information on
+ * memory ordering guarantees.
+ */
+void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
+{
+ call_rcu_tasks_generic(rhp, func, &rcu_tasks);
+}
+EXPORT_SYMBOL_GPL(call_rcu_tasks);
+
+/**
+ * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full rcu-tasks
+ * grace period has elapsed, in other words after all currently
+ * executing rcu-tasks read-side critical sections have elapsed. These
+ * read-side critical sections are delimited by calls to schedule(),
+ * cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls
+ * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
+ *
+ * This is a very specialized primitive, intended only for a few uses in
+ * tracing and other situations requiring manipulation of function
+ * preambles and profiling hooks. The synchronize_rcu_tasks() function
+ * is not (yet) intended for heavy use from multiple CPUs.
+ *
+ * See the description of synchronize_rcu() for more detailed information
+ * on memory ordering guarantees.
+ */
+void synchronize_rcu_tasks(void)
+{
+ synchronize_rcu_tasks_generic(&rcu_tasks);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
+
+/**
+ * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
+ *
+ * Although the current implementation is guaranteed to wait, it is not
+ * obligated to, for example, if there are no pending callbacks.
+ */
+void rcu_barrier_tasks(void)
+{
+ /* There is only one callback queue, so this is easy. ;-) */
+ synchronize_rcu_tasks();
+}
+EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
+
+static int __init rcu_spawn_tasks_kthread(void)
+{
+ rcu_tasks.gp_sleep = HZ / 10;
+ rcu_tasks.init_fract = 10;
+ rcu_tasks.pregp_func = rcu_tasks_pregp_step;
+ rcu_tasks.pertask_func = rcu_tasks_pertask;
+ rcu_tasks.postscan_func = rcu_tasks_postscan;
+ rcu_tasks.holdouts_func = check_all_holdout_tasks;
+ rcu_tasks.postgp_func = rcu_tasks_postgp;
+ rcu_spawn_tasks_kthread_generic(&rcu_tasks);
+ return 0;
+}
+
+#ifndef CONFIG_TINY_RCU
+static void show_rcu_tasks_classic_gp_kthread(void)
+{
+ show_rcu_tasks_generic_gp_kthread(&rcu_tasks, "");
+}
+#endif /* #ifndef CONFIG_TINY_RCU */
+
+/* Do the srcu_read_lock() for the above synchronize_srcu(). */
+void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
+{
+ preempt_disable();
+ current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
+ preempt_enable();
+}
+
+/* Do the srcu_read_unlock() for the above synchronize_srcu(). */
+void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu)
+{
+ struct task_struct *t = current;
+
+ preempt_disable();
+ __srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx);
+ preempt_enable();
+ exit_tasks_rcu_finish_trace(t);
+}
+
+#else /* #ifdef CONFIG_TASKS_RCU */
+static inline void show_rcu_tasks_classic_gp_kthread(void) { }
+void exit_tasks_rcu_start(void) { }
+void exit_tasks_rcu_finish(void) { exit_tasks_rcu_finish_trace(current); }
+#endif /* #else #ifdef CONFIG_TASKS_RCU */
+
+#ifdef CONFIG_TASKS_RUDE_RCU
+
+////////////////////////////////////////////////////////////////////////
+//
+// "Rude" variant of Tasks RCU, inspired by Steve Rostedt's trick of
+// passing an empty function to schedule_on_each_cpu(). This approach
+// provides an asynchronous call_rcu_tasks_rude() API and batching
+// of concurrent calls to the synchronous synchronize_rcu_rude() API.
+// This sends IPIs far and wide and induces otherwise unnecessary context
+// switches on all online CPUs, whether idle or not.
+
+// Empty function to allow workqueues to force a context switch.
+static void rcu_tasks_be_rude(struct work_struct *work)
+{
+}
+
+// Wait for one rude RCU-tasks grace period.
+static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp)
+{
+ rtp->n_ipis += cpumask_weight(cpu_online_mask);
+ schedule_on_each_cpu(rcu_tasks_be_rude);
+}
+
+void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func);
+DEFINE_RCU_TASKS(rcu_tasks_rude, rcu_tasks_rude_wait_gp, call_rcu_tasks_rude,
+ "RCU Tasks Rude");
+
+/**
+ * call_rcu_tasks_rude() - Queue a callback rude task-based grace period
+ * @rhp: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. call_rcu_tasks_rude()
+ * assumes that the read-side critical sections end at context switch,
+ * cond_resched_rcu_qs(), or transition to usermode execution. As such,
+ * there are no read-side primitives analogous to rcu_read_lock() and
+ * rcu_read_unlock() because this primitive is intended to determine
+ * that all tasks have passed through a safe state, not so much for
+ * data-strcuture synchronization.
+ *
+ * See the description of call_rcu() for more detailed information on
+ * memory ordering guarantees.
+ */
+void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func)
+{
+ call_rcu_tasks_generic(rhp, func, &rcu_tasks_rude);
+}
+EXPORT_SYMBOL_GPL(call_rcu_tasks_rude);
+
+/**
+ * synchronize_rcu_tasks_rude - wait for a rude rcu-tasks grace period
+ *
+ * Control will return to the caller some time after a rude rcu-tasks
+ * grace period has elapsed, in other words after all currently
+ * executing rcu-tasks read-side critical sections have elapsed. These
+ * read-side critical sections are delimited by calls to schedule(),
+ * cond_resched_tasks_rcu_qs(), userspace execution, and (in theory,
+ * anyway) cond_resched().
+ *
+ * This is a very specialized primitive, intended only for a few uses in
+ * tracing and other situations requiring manipulation of function preambles
+ * and profiling hooks. The synchronize_rcu_tasks_rude() function is not
+ * (yet) intended for heavy use from multiple CPUs.
+ *
+ * See the description of synchronize_rcu() for more detailed information
+ * on memory ordering guarantees.
+ */
+void synchronize_rcu_tasks_rude(void)
+{
+ synchronize_rcu_tasks_generic(&rcu_tasks_rude);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_rude);
+
+/**
+ * rcu_barrier_tasks_rude - Wait for in-flight call_rcu_tasks_rude() callbacks.
+ *
+ * Although the current implementation is guaranteed to wait, it is not
+ * obligated to, for example, if there are no pending callbacks.
+ */
+void rcu_barrier_tasks_rude(void)
+{
+ /* There is only one callback queue, so this is easy. ;-) */
+ synchronize_rcu_tasks_rude();
+}
+EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude);
+
+static int __init rcu_spawn_tasks_rude_kthread(void)
+{
+ rcu_tasks_rude.gp_sleep = HZ / 10;
+ rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude);
+ return 0;
+}
+
+#ifndef CONFIG_TINY_RCU
+static void show_rcu_tasks_rude_gp_kthread(void)
+{
+ show_rcu_tasks_generic_gp_kthread(&rcu_tasks_rude, "");
+}
+#endif /* #ifndef CONFIG_TINY_RCU */
+
+#else /* #ifdef CONFIG_TASKS_RUDE_RCU */
+static void show_rcu_tasks_rude_gp_kthread(void) {}
+#endif /* #else #ifdef CONFIG_TASKS_RUDE_RCU */
+
+////////////////////////////////////////////////////////////////////////
+//
+// Tracing variant of Tasks RCU. This variant is designed to be used
+// to protect tracing hooks, including those of BPF. This variant
+// therefore:
+//
+// 1. Has explicit read-side markers to allow finite grace periods
+// in the face of in-kernel loops for PREEMPT=n builds.
+//
+// 2. Protects code in the idle loop, exception entry/exit, and
+// CPU-hotplug code paths, similar to the capabilities of SRCU.
+//
+// 3. Avoids expensive read-side instruction, having overhead similar
+// to that of Preemptible RCU.
+//
+// There are of course downsides. The grace-period code can send IPIs to
+// CPUs, even when those CPUs are in the idle loop or in nohz_full userspace.
+// It is necessary to scan the full tasklist, much as for Tasks RCU. There
+// is a single callback queue guarded by a single lock, again, much as for
+// Tasks RCU. If needed, these downsides can be at least partially remedied.
+//
+// Perhaps most important, this variant of RCU does not affect the vanilla
+// flavors, rcu_preempt and rcu_sched. The fact that RCU Tasks Trace
+// readers can operate from idle, offline, and exception entry/exit in no
+// way allows rcu_preempt and rcu_sched readers to also do so.
+
+// The lockdep state must be outside of #ifdef to be useful.
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+static struct lock_class_key rcu_lock_trace_key;
+struct lockdep_map rcu_trace_lock_map =
+ STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_trace", &rcu_lock_trace_key);
+EXPORT_SYMBOL_GPL(rcu_trace_lock_map);
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+#ifdef CONFIG_TASKS_TRACE_RCU
+
+static atomic_t trc_n_readers_need_end; // Number of waited-for readers.
+static DECLARE_WAIT_QUEUE_HEAD(trc_wait); // List of holdout tasks.
+
+// Record outstanding IPIs to each CPU. No point in sending two...
+static DEFINE_PER_CPU(bool, trc_ipi_to_cpu);
+
+// The number of detections of task quiescent state relying on
+// heavyweight readers executing explicit memory barriers.
+static unsigned long n_heavy_reader_attempts;
+static unsigned long n_heavy_reader_updates;
+static unsigned long n_heavy_reader_ofl_updates;
+
+void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
+DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace,
+ "RCU Tasks Trace");
+
+/*
+ * This irq_work handler allows rcu_read_unlock_trace() to be invoked
+ * while the scheduler locks are held.
+ */
+static void rcu_read_unlock_iw(struct irq_work *iwp)
+{
+ wake_up(&trc_wait);
+}
+static DEFINE_IRQ_WORK(rcu_tasks_trace_iw, rcu_read_unlock_iw);
+
+/* If we are the last reader, wake up the grace-period kthread. */
+void rcu_read_unlock_trace_special(struct task_struct *t, int nesting)
+{
+ int nq = t->trc_reader_special.b.need_qs;
+
+ if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) &&
+ t->trc_reader_special.b.need_mb)
+ smp_mb(); // Pairs with update-side barriers.
+ // Update .need_qs before ->trc_reader_nesting for irq/NMI handlers.
+ if (nq)
+ WRITE_ONCE(t->trc_reader_special.b.need_qs, false);
+ WRITE_ONCE(t->trc_reader_nesting, nesting);
+ if (nq && atomic_dec_and_test(&trc_n_readers_need_end))
+ irq_work_queue(&rcu_tasks_trace_iw);
+}
+EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special);
+
+/* Add a task to the holdout list, if it is not already on the list. */
+static void trc_add_holdout(struct task_struct *t, struct list_head *bhp)
+{
+ if (list_empty(&t->trc_holdout_list)) {
+ get_task_struct(t);
+ list_add(&t->trc_holdout_list, bhp);
+ }
+}
+
+/* Remove a task from the holdout list, if it is in fact present. */
+static void trc_del_holdout(struct task_struct *t)
+{
+ if (!list_empty(&t->trc_holdout_list)) {
+ list_del_init(&t->trc_holdout_list);
+ put_task_struct(t);
+ }
+}
+
+/* IPI handler to check task state. */
+static void trc_read_check_handler(void *t_in)
+{
+ struct task_struct *t = current;
+ struct task_struct *texp = t_in;
+
+ // If the task is no longer running on this CPU, leave.
+ if (unlikely(texp != t)) {
+ if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end)))
+ wake_up(&trc_wait);
+ goto reset_ipi; // Already on holdout list, so will check later.
+ }
+
+ // If the task is not in a read-side critical section, and
+ // if this is the last reader, awaken the grace-period kthread.
+ if (likely(!t->trc_reader_nesting)) {
+ if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end)))
+ wake_up(&trc_wait);
+ // Mark as checked after decrement to avoid false
+ // positives on the above WARN_ON_ONCE().
+ WRITE_ONCE(t->trc_reader_checked, true);
+ goto reset_ipi;
+ }
+ // If we are racing with an rcu_read_unlock_trace(), try again later.
+ if (unlikely(t->trc_reader_nesting < 0)) {
+ if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end)))
+ wake_up(&trc_wait);
+ goto reset_ipi;
+ }
+ WRITE_ONCE(t->trc_reader_checked, true);
+
+ // Get here if the task is in a read-side critical section. Set
+ // its state so that it will awaken the grace-period kthread upon
+ // exit from that critical section.
+ WARN_ON_ONCE(t->trc_reader_special.b.need_qs);
+ WRITE_ONCE(t->trc_reader_special.b.need_qs, true);
+
+reset_ipi:
+ // Allow future IPIs to be sent on CPU and for task.
+ // Also order this IPI handler against any later manipulations of
+ // the intended task.
+ smp_store_release(&per_cpu(trc_ipi_to_cpu, smp_processor_id()), false); // ^^^
+ smp_store_release(&texp->trc_ipi_to_cpu, -1); // ^^^
+}
+
+/* Callback function for scheduler to check locked-down task. */
+static bool trc_inspect_reader(struct task_struct *t, void *arg)
+{
+ int cpu = task_cpu(t);
+ bool in_qs = false;
+ bool ofl = cpu_is_offline(cpu);
+
+ if (task_curr(t)) {
+ WARN_ON_ONCE(ofl && !is_idle_task(t));
+
+ // If no chance of heavyweight readers, do it the hard way.
+ if (!ofl && !IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
+ return false;
+
+ // If heavyweight readers are enabled on the remote task,
+ // we can inspect its state despite its currently running.
+ // However, we cannot safely change its state.
+ n_heavy_reader_attempts++;
+ if (!ofl && // Check for "running" idle tasks on offline CPUs.
+ !rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting))
+ return false; // No quiescent state, do it the hard way.
+ n_heavy_reader_updates++;
+ if (ofl)
+ n_heavy_reader_ofl_updates++;
+ in_qs = true;
+ } else {
+ in_qs = likely(!t->trc_reader_nesting);
+ }
+
+ // Mark as checked so that the grace-period kthread will
+ // remove it from the holdout list.
+ t->trc_reader_checked = true;
+
+ if (in_qs)
+ return true; // Already in quiescent state, done!!!
+
+ // The task is in a read-side critical section, so set up its
+ // state so that it will awaken the grace-period kthread upon exit
+ // from that critical section.
+ atomic_inc(&trc_n_readers_need_end); // One more to wait on.
+ WARN_ON_ONCE(t->trc_reader_special.b.need_qs);
+ WRITE_ONCE(t->trc_reader_special.b.need_qs, true);
+ return true;
+}
+
+/* Attempt to extract the state for the specified task. */
+static void trc_wait_for_one_reader(struct task_struct *t,
+ struct list_head *bhp)
+{
+ int cpu;
+
+ // If a previous IPI is still in flight, let it complete.
+ if (smp_load_acquire(&t->trc_ipi_to_cpu) != -1) // Order IPI
+ return;
+
+ // The current task had better be in a quiescent state.
+ if (t == current) {
+ t->trc_reader_checked = true;
+ WARN_ON_ONCE(t->trc_reader_nesting);
+ return;
+ }
+
+ // Attempt to nail down the task for inspection.
+ get_task_struct(t);
+ if (try_invoke_on_locked_down_task(t, trc_inspect_reader, NULL)) {
+ put_task_struct(t);
+ return;
+ }
+ put_task_struct(t);
+
+ // If currently running, send an IPI, either way, add to list.
+ trc_add_holdout(t, bhp);
+ if (task_curr(t) &&
+ time_after(jiffies + 1, rcu_tasks_trace.gp_start + rcu_task_ipi_delay)) {
+ // The task is currently running, so try IPIing it.
+ cpu = task_cpu(t);
+
+ // If there is already an IPI outstanding, let it happen.
+ if (per_cpu(trc_ipi_to_cpu, cpu) || t->trc_ipi_to_cpu >= 0)
+ return;
+
+ atomic_inc(&trc_n_readers_need_end);
+ per_cpu(trc_ipi_to_cpu, cpu) = true;
+ t->trc_ipi_to_cpu = cpu;
+ rcu_tasks_trace.n_ipis++;
+ if (smp_call_function_single(cpu,
+ trc_read_check_handler, t, 0)) {
+ // Just in case there is some other reason for
+ // failure than the target CPU being offline.
+ rcu_tasks_trace.n_ipis_fails++;
+ per_cpu(trc_ipi_to_cpu, cpu) = false;
+ t->trc_ipi_to_cpu = cpu;
+ if (atomic_dec_and_test(&trc_n_readers_need_end)) {
+ WARN_ON_ONCE(1);
+ wake_up(&trc_wait);
+ }
+ }
+ }
+}
+
+/* Initialize for a new RCU-tasks-trace grace period. */
+static void rcu_tasks_trace_pregp_step(void)
+{
+ int cpu;
+
+ // Allow for fast-acting IPIs.
+ atomic_set(&trc_n_readers_need_end, 1);
+
+ // There shouldn't be any old IPIs, but...
+ for_each_possible_cpu(cpu)
+ WARN_ON_ONCE(per_cpu(trc_ipi_to_cpu, cpu));
+
+ // Disable CPU hotplug across the tasklist scan.
+ // This also waits for all readers in CPU-hotplug code paths.
+ cpus_read_lock();
+}
+
+/* Do first-round processing for the specified task. */
+static void rcu_tasks_trace_pertask(struct task_struct *t,
+ struct list_head *hop)
+{
+ // During early boot when there is only the one boot CPU, there
+ // is no idle task for the other CPUs. Just return.
+ if (unlikely(t == NULL))
+ return;
+
+ WRITE_ONCE(t->trc_reader_special.b.need_qs, false);
+ WRITE_ONCE(t->trc_reader_checked, false);
+ t->trc_ipi_to_cpu = -1;
+ trc_wait_for_one_reader(t, hop);
+}
+
+/*
+ * Do intermediate processing between task and holdout scans and
+ * pick up the idle tasks.
+ */
+static void rcu_tasks_trace_postscan(struct list_head *hop)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ rcu_tasks_trace_pertask(idle_task(cpu), hop);
+
+ // Re-enable CPU hotplug now that the tasklist scan has completed.
+ cpus_read_unlock();
+
+ // Wait for late-stage exiting tasks to finish exiting.
+ // These might have passed the call to exit_tasks_rcu_finish().
+ synchronize_rcu();
+ // Any tasks that exit after this point will set ->trc_reader_checked.
+}
+
+/* Show the state of a task stalling the current RCU tasks trace GP. */
+static void show_stalled_task_trace(struct task_struct *t, bool *firstreport)
+{
+ int cpu;
+
+ if (*firstreport) {
+ pr_err("INFO: rcu_tasks_trace detected stalls on tasks:\n");
+ *firstreport = false;
+ }
+ // FIXME: This should attempt to use try_invoke_on_nonrunning_task().
+ cpu = task_cpu(t);
+ pr_alert("P%d: %c%c%c nesting: %d%c cpu: %d\n",
+ t->pid,
+ ".I"[READ_ONCE(t->trc_ipi_to_cpu) > 0],
+ ".i"[is_idle_task(t)],
+ ".N"[cpu > 0 && tick_nohz_full_cpu(cpu)],
+ t->trc_reader_nesting,
+ " N"[!!t->trc_reader_special.b.need_qs],
+ cpu);
+ sched_show_task(t);
+}
+
+/* List stalled IPIs for RCU tasks trace. */
+static void show_stalled_ipi_trace(void)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ if (per_cpu(trc_ipi_to_cpu, cpu))
+ pr_alert("\tIPI outstanding to CPU %d\n", cpu);
+}
+
+/* Do one scan of the holdout list. */
+static void check_all_holdout_tasks_trace(struct list_head *hop,
+ bool needreport, bool *firstreport)
+{
+ struct task_struct *g, *t;
+
+ // Disable CPU hotplug across the holdout list scan.
+ cpus_read_lock();
+
+ list_for_each_entry_safe(t, g, hop, trc_holdout_list) {
+ // If safe and needed, try to check the current task.
+ if (READ_ONCE(t->trc_ipi_to_cpu) == -1 &&
+ !READ_ONCE(t->trc_reader_checked))
+ trc_wait_for_one_reader(t, hop);
+
+ // If check succeeded, remove this task from the list.
+ if (READ_ONCE(t->trc_reader_checked))
+ trc_del_holdout(t);
+ else if (needreport)
+ show_stalled_task_trace(t, firstreport);
+ }
+
+ // Re-enable CPU hotplug now that the holdout list scan has completed.
+ cpus_read_unlock();
+
+ if (needreport) {
+ if (firstreport)
+ pr_err("INFO: rcu_tasks_trace detected stalls? (Late IPI?)\n");
+ show_stalled_ipi_trace();
+ }
+}
+
+/* Wait for grace period to complete and provide ordering. */
+static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp)
+{
+ bool firstreport;
+ struct task_struct *g, *t;
+ LIST_HEAD(holdouts);
+ long ret;
+
+ // Remove the safety count.
+ smp_mb__before_atomic(); // Order vs. earlier atomics
+ atomic_dec(&trc_n_readers_need_end);
+ smp_mb__after_atomic(); // Order vs. later atomics
+
+ // Wait for readers.
+ set_tasks_gp_state(rtp, RTGS_WAIT_READERS);
+ for (;;) {
+ ret = wait_event_idle_exclusive_timeout(
+ trc_wait,
+ atomic_read(&trc_n_readers_need_end) == 0,
+ READ_ONCE(rcu_task_stall_timeout));
+ if (ret)
+ break; // Count reached zero.
+ // Stall warning time, so make a list of the offenders.
+ rcu_read_lock();
+ for_each_process_thread(g, t)
+ if (READ_ONCE(t->trc_reader_special.b.need_qs))
+ trc_add_holdout(t, &holdouts);
+ rcu_read_unlock();
+ firstreport = true;
+ list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list) {
+ if (READ_ONCE(t->trc_reader_special.b.need_qs))
+ show_stalled_task_trace(t, &firstreport);
+ trc_del_holdout(t); // Release task_struct reference.
+ }
+ if (firstreport)
+ pr_err("INFO: rcu_tasks_trace detected stalls? (Counter/taskslist mismatch?)\n");
+ show_stalled_ipi_trace();
+ pr_err("\t%d holdouts\n", atomic_read(&trc_n_readers_need_end));
+ }
+ smp_mb(); // Caller's code must be ordered after wakeup.
+ // Pairs with pretty much every ordering primitive.
+}
+
+/* Report any needed quiescent state for this exiting task. */
+static void exit_tasks_rcu_finish_trace(struct task_struct *t)
+{
+ WRITE_ONCE(t->trc_reader_checked, true);
+ WARN_ON_ONCE(t->trc_reader_nesting);
+ WRITE_ONCE(t->trc_reader_nesting, 0);
+ if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs)))
+ rcu_read_unlock_trace_special(t, 0);
+}
+
+/**
+ * call_rcu_tasks_trace() - Queue a callback trace task-based grace period
+ * @rhp: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. call_rcu_tasks_trace()
+ * assumes that the read-side critical sections end at context switch,
+ * cond_resched_rcu_qs(), or transition to usermode execution. As such,
+ * there are no read-side primitives analogous to rcu_read_lock() and
+ * rcu_read_unlock() because this primitive is intended to determine
+ * that all tasks have passed through a safe state, not so much for
+ * data-strcuture synchronization.
+ *
+ * See the description of call_rcu() for more detailed information on
+ * memory ordering guarantees.
+ */
+void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func)
+{
+ call_rcu_tasks_generic(rhp, func, &rcu_tasks_trace);
+}
+EXPORT_SYMBOL_GPL(call_rcu_tasks_trace);
+
+/**
+ * synchronize_rcu_tasks_trace - wait for a trace rcu-tasks grace period
+ *
+ * Control will return to the caller some time after a trace rcu-tasks
+ * grace period has elapsed, in other words after all currently executing
+ * rcu-tasks read-side critical sections have elapsed. These read-side
+ * critical sections are delimited by calls to rcu_read_lock_trace()
+ * and rcu_read_unlock_trace().
+ *
+ * This is a very specialized primitive, intended only for a few uses in
+ * tracing and other situations requiring manipulation of function preambles
+ * and profiling hooks. The synchronize_rcu_tasks_trace() function is not
+ * (yet) intended for heavy use from multiple CPUs.
+ *
+ * See the description of synchronize_rcu() for more detailed information
+ * on memory ordering guarantees.
+ */
+void synchronize_rcu_tasks_trace(void)
+{
+ RCU_LOCKDEP_WARN(lock_is_held(&rcu_trace_lock_map), "Illegal synchronize_rcu_tasks_trace() in RCU Tasks Trace read-side critical section");
+ synchronize_rcu_tasks_generic(&rcu_tasks_trace);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_trace);
+
+/**
+ * rcu_barrier_tasks_trace - Wait for in-flight call_rcu_tasks_trace() callbacks.
+ *
+ * Although the current implementation is guaranteed to wait, it is not
+ * obligated to, for example, if there are no pending callbacks.
+ */
+void rcu_barrier_tasks_trace(void)
+{
+ /* There is only one callback queue, so this is easy. ;-) */
+ synchronize_rcu_tasks_trace();
+}
+EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace);
+
+static int __init rcu_spawn_tasks_trace_kthread(void)
+{
+ if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) {
+ rcu_tasks_trace.gp_sleep = HZ / 10;
+ rcu_tasks_trace.init_fract = 10;
+ } else {
+ rcu_tasks_trace.gp_sleep = HZ / 200;
+ if (rcu_tasks_trace.gp_sleep <= 0)
+ rcu_tasks_trace.gp_sleep = 1;
+ rcu_tasks_trace.init_fract = HZ / 5;
+ if (rcu_tasks_trace.init_fract <= 0)
+ rcu_tasks_trace.init_fract = 1;
+ }
+ rcu_tasks_trace.pregp_func = rcu_tasks_trace_pregp_step;
+ rcu_tasks_trace.pertask_func = rcu_tasks_trace_pertask;
+ rcu_tasks_trace.postscan_func = rcu_tasks_trace_postscan;
+ rcu_tasks_trace.holdouts_func = check_all_holdout_tasks_trace;
+ rcu_tasks_trace.postgp_func = rcu_tasks_trace_postgp;
+ rcu_spawn_tasks_kthread_generic(&rcu_tasks_trace);
+ return 0;
+}
+
+#ifndef CONFIG_TINY_RCU
+static void show_rcu_tasks_trace_gp_kthread(void)
+{
+ char buf[64];
+
+ sprintf(buf, "N%d h:%lu/%lu/%lu", atomic_read(&trc_n_readers_need_end),
+ data_race(n_heavy_reader_ofl_updates),
+ data_race(n_heavy_reader_updates),
+ data_race(n_heavy_reader_attempts));
+ show_rcu_tasks_generic_gp_kthread(&rcu_tasks_trace, buf);
+}
+#endif /* #ifndef CONFIG_TINY_RCU */
+
+#else /* #ifdef CONFIG_TASKS_TRACE_RCU */
+static void exit_tasks_rcu_finish_trace(struct task_struct *t) { }
+static inline void show_rcu_tasks_trace_gp_kthread(void) {}
+#endif /* #else #ifdef CONFIG_TASKS_TRACE_RCU */
+
+#ifndef CONFIG_TINY_RCU
+void show_rcu_tasks_gp_kthreads(void)
+{
+ show_rcu_tasks_classic_gp_kthread();
+ show_rcu_tasks_rude_gp_kthread();
+ show_rcu_tasks_trace_gp_kthread();
+}
+#endif /* #ifndef CONFIG_TINY_RCU */
+
+void __init rcu_init_tasks_generic(void)
+{
+#ifdef CONFIG_TASKS_RCU
+ rcu_spawn_tasks_kthread();
+#endif
+
+#ifdef CONFIG_TASKS_RUDE_RCU
+ rcu_spawn_tasks_rude_kthread();
+#endif
+
+#ifdef CONFIG_TASKS_TRACE_RCU
+ rcu_spawn_tasks_trace_kthread();
+#endif
+}
+
+#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
+static inline void rcu_tasks_bootup_oddness(void) {}
+void show_rcu_tasks_gp_kthreads(void) {}
+#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */