diff options
Diffstat (limited to 'kernel/rcutiny_plugin.h')
| -rw-r--r-- | kernel/rcutiny_plugin.h | 1009 |
1 files changed, 35 insertions, 974 deletions
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 8a233002fae..0cd385acccf 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -53,958 +53,10 @@ static struct rcu_ctrlblk rcu_bh_ctrlblk = { }; #ifdef CONFIG_DEBUG_LOCK_ALLOC +#include <linux/kernel_stat.h> + int rcu_scheduler_active __read_mostly; EXPORT_SYMBOL_GPL(rcu_scheduler_active); -#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ - -#ifdef CONFIG_RCU_TRACE - -static void check_cpu_stall(struct rcu_ctrlblk *rcp) -{ - unsigned long j; - unsigned long js; - - if (rcu_cpu_stall_suppress) - return; - rcp->ticks_this_gp++; - j = jiffies; - js = rcp->jiffies_stall; - if (*rcp->curtail && ULONG_CMP_GE(j, js)) { - pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n", - rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting, - jiffies - rcp->gp_start, rcp->qlen); - dump_stack(); - } - if (*rcp->curtail && ULONG_CMP_GE(j, js)) - rcp->jiffies_stall = jiffies + - 3 * rcu_jiffies_till_stall_check() + 3; - else if (ULONG_CMP_GE(j, js)) - rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check(); -} - -static void check_cpu_stall_preempt(void); - -#endif /* #ifdef CONFIG_RCU_TRACE */ - -static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp) -{ -#ifdef CONFIG_RCU_TRACE - rcp->ticks_this_gp = 0; - rcp->gp_start = jiffies; - rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check(); -#endif /* #ifdef CONFIG_RCU_TRACE */ -} - -static void check_cpu_stalls(void) -{ - RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk)); - RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk)); - RCU_TRACE(check_cpu_stall_preempt()); -} - -#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++); - reset_cpu_stall_ticks(&rcu_preempt_ctrlblk.rcb); - - /* 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(). */ - if (rcu_expedited) - synchronize_rcu_expedited(); - else - 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 @@ -1020,25 +72,6 @@ void __init rcu_scheduler_starting(void) #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; @@ -1053,7 +86,6 @@ static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n) */ 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; @@ -1103,11 +135,40 @@ MODULE_AUTHOR("Paul E. McKenney"); MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation"); MODULE_LICENSE("GPL"); -static void check_cpu_stall_preempt(void) +static void check_cpu_stall(struct rcu_ctrlblk *rcp) { -#ifdef CONFIG_TINY_PREEMPT_RCU - check_cpu_stall(&rcu_preempt_ctrlblk.rcb); -#endif /* #ifdef CONFIG_TINY_PREEMPT_RCU */ + unsigned long j; + unsigned long js; + + if (rcu_cpu_stall_suppress) + return; + rcp->ticks_this_gp++; + j = jiffies; + js = rcp->jiffies_stall; + if (*rcp->curtail && ULONG_CMP_GE(j, js)) { + pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n", + rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting, + jiffies - rcp->gp_start, rcp->qlen); + dump_stack(); + } + if (*rcp->curtail && ULONG_CMP_GE(j, js)) + rcp->jiffies_stall = jiffies + + 3 * rcu_jiffies_till_stall_check() + 3; + else if (ULONG_CMP_GE(j, js)) + rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check(); +} + +static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp) +{ + rcp->ticks_this_gp = 0; + rcp->gp_start = jiffies; + rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check(); +} + +static void check_cpu_stalls(void) +{ + RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk)); + RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk)); } #endif /* #ifdef CONFIG_RCU_TRACE */ |