/* * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition * Internal non-public definitions that provide either classic * 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 * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * * 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 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. */ 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) { 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; 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); } /* * 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. */ 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); } /* * 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) { return rcu_preempt_ctrlblk.rcb.rcucblist != NULL; } #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 __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; local_irq_save(flags); rcp->qlen -= n; 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 */