| Author | Tokens | Token Proportion | Commits | Commit Proportion |
|---|---|---|---|---|
| Paul E. McKenney | 7228 | 87.04% | 155 | 79.49% |
| Uladzislau Rezki | 338 | 4.07% | 2 | 1.03% |
| Neeraj Upadhyay | 279 | 3.36% | 8 | 4.10% |
| Zqiang | 150 | 1.81% | 7 | 3.59% |
| Frédéric Weisbecker | 91 | 1.10% | 5 | 2.56% |
| Waiman Long | 70 | 0.84% | 1 | 0.51% |
| Sebastian Andrzej Siewior | 35 | 0.42% | 2 | 1.03% |
| Eric Dumazet | 26 | 0.31% | 1 | 0.51% |
| Mathieu Desnoyers | 24 | 0.29% | 1 | 0.51% |
| Pavel Machek | 15 | 0.18% | 1 | 0.51% |
| Andrew Morton | 12 | 0.14% | 2 | 1.03% |
| Peter Zijlstra | 8 | 0.10% | 1 | 0.51% |
| Boqun Feng | 7 | 0.08% | 1 | 0.51% |
| Zhen Lei | 5 | 0.06% | 1 | 0.51% |
| Ian Campbell | 4 | 0.05% | 1 | 0.51% |
| Nikita Kiryushin | 3 | 0.04% | 1 | 0.51% |
| Andrew Lutomirski | 3 | 0.04% | 1 | 0.51% |
| Liu Song | 2 | 0.02% | 1 | 0.51% |
| Linus Torvalds | 2 | 0.02% | 1 | 0.51% |
| Steven Rostedt | 1 | 0.01% | 1 | 0.51% |
| Jiapeng Chong | 1 | 0.01% | 1 | 0.51% |
| Total | 8304 | 195 |
/* SPDX-License-Identifier: GPL-2.0+ */ /* * Task-based RCU implementations. * * Copyright (C) 2020 Paul E. McKenney */ #ifdef CONFIG_TASKS_RCU_GENERIC #include "rcu_segcblist.h" //////////////////////////////////////////////////////////////////////// // // Generic data structures. struct rcu_tasks; typedef void (*rcu_tasks_gp_func_t)(struct rcu_tasks *rtp); typedef void (*pregp_func_t)(struct list_head *hop); 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); /** * struct rcu_tasks_percpu - Per-CPU component of definition for a Tasks-RCU-like mechanism. * @cblist: Callback list. * @lock: Lock protecting per-CPU callback list. * @rtp_jiffies: Jiffies counter value for statistics. * @lazy_timer: Timer to unlazify callbacks. * @urgent_gp: Number of additional non-lazy grace periods. * @rtp_n_lock_retries: Rough lock-contention statistic. * @rtp_work: Work queue for invoking callbacks. * @rtp_irq_work: IRQ work queue for deferred wakeups. * @barrier_q_head: RCU callback for barrier operation. * @rtp_blkd_tasks: List of tasks blocked as readers. * @rtp_exit_list: List of tasks in the latter portion of do_exit(). * @cpu: CPU number corresponding to this entry. * @rtpp: Pointer to the rcu_tasks structure. */ struct rcu_tasks_percpu { struct rcu_segcblist cblist; raw_spinlock_t __private lock; unsigned long rtp_jiffies; unsigned long rtp_n_lock_retries; struct timer_list lazy_timer; unsigned int urgent_gp; struct work_struct rtp_work; struct irq_work rtp_irq_work; struct rcu_head barrier_q_head; struct list_head rtp_blkd_tasks; struct list_head rtp_exit_list; int cpu; struct rcu_tasks *rtpp; }; /** * struct rcu_tasks - Definition for a Tasks-RCU-like mechanism. * @cbs_wait: RCU wait allowing a new callback to get kthread's attention. * @cbs_gbl_lock: Lock protecting callback list. * @tasks_gp_mutex: Mutex protecting grace period, needed during mid-boot dead zone. * @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. * @tasks_gp_seq: 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. * @kthread_ptr: This flavor's grace-period/callback-invocation kthread. * @lazy_jiffies: Number of jiffies to allow callbacks to be lazy. * @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). * @holdouts_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. * @wait_state: Task state for synchronous grace-period waits (default TASK_UNINTERRUPTIBLE). * @rtpcpu: This flavor's rcu_tasks_percpu structure. * @percpu_enqueue_shift: Shift down CPU ID this much when enqueuing callbacks. * @percpu_enqueue_lim: Number of per-CPU callback queues in use for enqueuing. * @percpu_dequeue_lim: Number of per-CPU callback queues in use for dequeuing. * @percpu_dequeue_gpseq: RCU grace-period number to propagate enqueue limit to dequeuers. * @barrier_q_mutex: Serialize barrier operations. * @barrier_q_count: Number of queues being waited on. * @barrier_q_completion: Barrier wait/wakeup mechanism. * @barrier_q_seq: Sequence number for barrier operations. * @name: This flavor's textual name. * @kname: This flavor's kthread name. */ struct rcu_tasks { struct rcuwait cbs_wait; raw_spinlock_t cbs_gbl_lock; struct mutex tasks_gp_mutex; int gp_state; int gp_sleep; int init_fract; unsigned long gp_jiffies; unsigned long gp_start; unsigned long tasks_gp_seq; unsigned long n_ipis; unsigned long n_ipis_fails; struct task_struct *kthread_ptr; unsigned long lazy_jiffies; 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; unsigned int wait_state; struct rcu_tasks_percpu __percpu *rtpcpu; int percpu_enqueue_shift; int percpu_enqueue_lim; int percpu_dequeue_lim; unsigned long percpu_dequeue_gpseq; struct mutex barrier_q_mutex; atomic_t barrier_q_count; struct completion barrier_q_completion; unsigned long barrier_q_seq; char *name; char *kname; }; static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp); #define DEFINE_RCU_TASKS(rt_name, gp, call, n) \ static DEFINE_PER_CPU(struct rcu_tasks_percpu, rt_name ## __percpu) = { \ .lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name ## __percpu.cbs_pcpu_lock), \ .rtp_irq_work = IRQ_WORK_INIT_HARD(call_rcu_tasks_iw_wakeup), \ }; \ static struct rcu_tasks rt_name = \ { \ .cbs_wait = __RCUWAIT_INITIALIZER(rt_name.wait), \ .cbs_gbl_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_gbl_lock), \ .tasks_gp_mutex = __MUTEX_INITIALIZER(rt_name.tasks_gp_mutex), \ .gp_func = gp, \ .call_func = call, \ .wait_state = TASK_UNINTERRUPTIBLE, \ .rtpcpu = &rt_name ## __percpu, \ .lazy_jiffies = DIV_ROUND_UP(HZ, 4), \ .name = n, \ .percpu_enqueue_shift = order_base_2(CONFIG_NR_CPUS), \ .percpu_enqueue_lim = 1, \ .percpu_dequeue_lim = 1, \ .barrier_q_mutex = __MUTEX_INITIALIZER(rt_name.barrier_q_mutex), \ .barrier_q_seq = (0UL - 50UL) << RCU_SEQ_CTR_SHIFT, \ .kname = #rt_name, \ } #ifdef CONFIG_TASKS_RCU /* Report delay of scan exiting tasklist in rcu_tasks_postscan(). */ static void tasks_rcu_exit_srcu_stall(struct timer_list *unused); static DEFINE_TIMER(tasks_rcu_exit_srcu_stall_timer, tasks_rcu_exit_srcu_stall); #endif /* 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_BOOT_STALL_TIMEOUT (HZ * 30) #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); #define RCU_TASK_STALL_INFO (HZ * 10) static int rcu_task_stall_info __read_mostly = RCU_TASK_STALL_INFO; module_param(rcu_task_stall_info, int, 0644); static int rcu_task_stall_info_mult __read_mostly = 3; module_param(rcu_task_stall_info_mult, int, 0444); static int rcu_task_enqueue_lim __read_mostly = -1; module_param(rcu_task_enqueue_lim, int, 0444); static bool rcu_task_cb_adjust; static int rcu_task_contend_lim __read_mostly = 100; module_param(rcu_task_contend_lim, int, 0444); static int rcu_task_collapse_lim __read_mostly = 10; module_param(rcu_task_collapse_lim, int, 0444); static int rcu_task_lazy_lim __read_mostly = 32; module_param(rcu_task_lazy_lim, int, 0444); /* 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. static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp); /* 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 */ // Initialize per-CPU callback lists for the specified flavor of // Tasks RCU. Do not enqueue callbacks before this function is invoked. static void cblist_init_generic(struct rcu_tasks *rtp) { int cpu; int lim; int shift; if (rcu_task_enqueue_lim < 0) { rcu_task_enqueue_lim = 1; rcu_task_cb_adjust = true; } else if (rcu_task_enqueue_lim == 0) { rcu_task_enqueue_lim = 1; } lim = rcu_task_enqueue_lim; if (lim > nr_cpu_ids) lim = nr_cpu_ids; shift = ilog2(nr_cpu_ids / lim); if (((nr_cpu_ids - 1) >> shift) >= lim) shift++; WRITE_ONCE(rtp->percpu_enqueue_shift, shift); WRITE_ONCE(rtp->percpu_dequeue_lim, lim); smp_store_release(&rtp->percpu_enqueue_lim, lim); for_each_possible_cpu(cpu) { struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); WARN_ON_ONCE(!rtpcp); if (cpu) raw_spin_lock_init(&ACCESS_PRIVATE(rtpcp, lock)); if (rcu_segcblist_empty(&rtpcp->cblist)) rcu_segcblist_init(&rtpcp->cblist); INIT_WORK(&rtpcp->rtp_work, rcu_tasks_invoke_cbs_wq); rtpcp->cpu = cpu; rtpcp->rtpp = rtp; if (!rtpcp->rtp_blkd_tasks.next) INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks); if (!rtpcp->rtp_exit_list.next) INIT_LIST_HEAD(&rtpcp->rtp_exit_list); } pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d.\n", rtp->name, data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim), rcu_task_cb_adjust); } // Compute wakeup time for lazy callback timer. static unsigned long rcu_tasks_lazy_time(struct rcu_tasks *rtp) { return jiffies + rtp->lazy_jiffies; } // Timer handler that unlazifies lazy callbacks. static void call_rcu_tasks_generic_timer(struct timer_list *tlp) { unsigned long flags; bool needwake = false; struct rcu_tasks *rtp; struct rcu_tasks_percpu *rtpcp = from_timer(rtpcp, tlp, lazy_timer); rtp = rtpcp->rtpp; raw_spin_lock_irqsave_rcu_node(rtpcp, flags); if (!rcu_segcblist_empty(&rtpcp->cblist) && rtp->lazy_jiffies) { if (!rtpcp->urgent_gp) rtpcp->urgent_gp = 1; needwake = true; mod_timer(&rtpcp->lazy_timer, rcu_tasks_lazy_time(rtp)); } raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); if (needwake) rcuwait_wake_up(&rtp->cbs_wait); } // IRQ-work handler that does deferred wakeup for call_rcu_tasks_generic(). static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp) { struct rcu_tasks *rtp; struct rcu_tasks_percpu *rtpcp = container_of(iwp, struct rcu_tasks_percpu, rtp_irq_work); rtp = rtpcp->rtpp; rcuwait_wake_up(&rtp->cbs_wait); } // 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) { int chosen_cpu; unsigned long flags; bool havekthread = smp_load_acquire(&rtp->kthread_ptr); int ideal_cpu; unsigned long j; bool needadjust = false; bool needwake; struct rcu_tasks_percpu *rtpcp; rhp->next = NULL; rhp->func = func; local_irq_save(flags); rcu_read_lock(); ideal_cpu = smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift); chosen_cpu = cpumask_next(ideal_cpu - 1, cpu_possible_mask); rtpcp = per_cpu_ptr(rtp->rtpcpu, chosen_cpu); if (!raw_spin_trylock_rcu_node(rtpcp)) { // irqs already disabled. raw_spin_lock_rcu_node(rtpcp); // irqs already disabled. j = jiffies; if (rtpcp->rtp_jiffies != j) { rtpcp->rtp_jiffies = j; rtpcp->rtp_n_lock_retries = 0; } if (rcu_task_cb_adjust && ++rtpcp->rtp_n_lock_retries > rcu_task_contend_lim && READ_ONCE(rtp->percpu_enqueue_lim) != nr_cpu_ids) needadjust = true; // Defer adjustment to avoid deadlock. } // Queuing callbacks before initialization not yet supported. if (WARN_ON_ONCE(!rcu_segcblist_is_enabled(&rtpcp->cblist))) rcu_segcblist_init(&rtpcp->cblist); needwake = (func == wakeme_after_rcu) || (rcu_segcblist_n_cbs(&rtpcp->cblist) == rcu_task_lazy_lim); if (havekthread && !needwake && !timer_pending(&rtpcp->lazy_timer)) { if (rtp->lazy_jiffies) mod_timer(&rtpcp->lazy_timer, rcu_tasks_lazy_time(rtp)); else needwake = rcu_segcblist_empty(&rtpcp->cblist); } if (needwake) rtpcp->urgent_gp = 3; rcu_segcblist_enqueue(&rtpcp->cblist, rhp); raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); if (unlikely(needadjust)) { raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); if (rtp->percpu_enqueue_lim != nr_cpu_ids) { WRITE_ONCE(rtp->percpu_enqueue_shift, 0); WRITE_ONCE(rtp->percpu_dequeue_lim, nr_cpu_ids); smp_store_release(&rtp->percpu_enqueue_lim, nr_cpu_ids); pr_info("Switching %s to per-CPU callback queuing.\n", rtp->name); } raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); } rcu_read_unlock(); /* We can't create the thread unless interrupts are enabled. */ if (needwake && READ_ONCE(rtp->kthread_ptr)) irq_work_queue(&rtpcp->rtp_irq_work); } // RCU callback function for rcu_barrier_tasks_generic(). static void rcu_barrier_tasks_generic_cb(struct rcu_head *rhp) { struct rcu_tasks *rtp; struct rcu_tasks_percpu *rtpcp; rtpcp = container_of(rhp, struct rcu_tasks_percpu, barrier_q_head); rtp = rtpcp->rtpp; if (atomic_dec_and_test(&rtp->barrier_q_count)) complete(&rtp->barrier_q_completion); } // Wait for all in-flight callbacks for the specified RCU Tasks flavor. // Operates in a manner similar to rcu_barrier(). static void rcu_barrier_tasks_generic(struct rcu_tasks *rtp) { int cpu; unsigned long flags; struct rcu_tasks_percpu *rtpcp; unsigned long s = rcu_seq_snap(&rtp->barrier_q_seq); mutex_lock(&rtp->barrier_q_mutex); if (rcu_seq_done(&rtp->barrier_q_seq, s)) { smp_mb(); mutex_unlock(&rtp->barrier_q_mutex); return; } rcu_seq_start(&rtp->barrier_q_seq); init_completion(&rtp->barrier_q_completion); atomic_set(&rtp->barrier_q_count, 2); for_each_possible_cpu(cpu) { if (cpu >= smp_load_acquire(&rtp->percpu_dequeue_lim)) break; rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); rtpcp->barrier_q_head.func = rcu_barrier_tasks_generic_cb; raw_spin_lock_irqsave_rcu_node(rtpcp, flags); if (rcu_segcblist_entrain(&rtpcp->cblist, &rtpcp->barrier_q_head)) atomic_inc(&rtp->barrier_q_count); raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); } if (atomic_sub_and_test(2, &rtp->barrier_q_count)) complete(&rtp->barrier_q_completion); wait_for_completion(&rtp->barrier_q_completion); rcu_seq_end(&rtp->barrier_q_seq); mutex_unlock(&rtp->barrier_q_mutex); } // Advance callbacks and indicate whether either a grace period or // callback invocation is needed. static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp) { int cpu; int dequeue_limit; unsigned long flags; bool gpdone = poll_state_synchronize_rcu(rtp->percpu_dequeue_gpseq); long n; long ncbs = 0; long ncbsnz = 0; int needgpcb = 0; dequeue_limit = smp_load_acquire(&rtp->percpu_dequeue_lim); for (cpu = 0; cpu < dequeue_limit; cpu++) { struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); /* Advance and accelerate any new callbacks. */ if (!rcu_segcblist_n_cbs(&rtpcp->cblist)) continue; raw_spin_lock_irqsave_rcu_node(rtpcp, flags); // Should we shrink down to a single callback queue? n = rcu_segcblist_n_cbs(&rtpcp->cblist); if (n) { ncbs += n; if (cpu > 0) ncbsnz += n; } rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq)); (void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq)); if (rtpcp->urgent_gp > 0 && rcu_segcblist_pend_cbs(&rtpcp->cblist)) { if (rtp->lazy_jiffies) rtpcp->urgent_gp--; needgpcb |= 0x3; } else if (rcu_segcblist_empty(&rtpcp->cblist)) { rtpcp->urgent_gp = 0; } if (rcu_segcblist_ready_cbs(&rtpcp->cblist)) needgpcb |= 0x1; raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); } // Shrink down to a single callback queue if appropriate. // This is done in two stages: (1) If there are no more than // rcu_task_collapse_lim callbacks on CPU 0 and none on any other // CPU, limit enqueueing to CPU 0. (2) After an RCU grace period, // if there has not been an increase in callbacks, limit dequeuing // to CPU 0. Note the matching RCU read-side critical section in // call_rcu_tasks_generic(). if (rcu_task_cb_adjust && ncbs <= rcu_task_collapse_lim) { raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); if (rtp->percpu_enqueue_lim > 1) { WRITE_ONCE(rtp->percpu_enqueue_shift, order_base_2(nr_cpu_ids)); smp_store_release(&rtp->percpu_enqueue_lim, 1); rtp->percpu_dequeue_gpseq = get_state_synchronize_rcu(); gpdone = false; pr_info("Starting switch %s to CPU-0 callback queuing.\n", rtp->name); } raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); } if (rcu_task_cb_adjust && !ncbsnz && gpdone) { raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); if (rtp->percpu_enqueue_lim < rtp->percpu_dequeue_lim) { WRITE_ONCE(rtp->percpu_dequeue_lim, 1); pr_info("Completing switch %s to CPU-0 callback queuing.\n", rtp->name); } if (rtp->percpu_dequeue_lim == 1) { for (cpu = rtp->percpu_dequeue_lim; cpu < nr_cpu_ids; cpu++) { struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); WARN_ON_ONCE(rcu_segcblist_n_cbs(&rtpcp->cblist)); } } raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); } return needgpcb; } // Advance callbacks and invoke any that are ready. static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu *rtpcp) { int cpu; int cpunext; int cpuwq; unsigned long flags; int len; struct rcu_head *rhp; struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); struct rcu_tasks_percpu *rtpcp_next; cpu = rtpcp->cpu; cpunext = cpu * 2 + 1; if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) { rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext); cpuwq = rcu_cpu_beenfullyonline(cpunext) ? cpunext : WORK_CPU_UNBOUND; queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work); cpunext++; if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) { rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext); cpuwq = rcu_cpu_beenfullyonline(cpunext) ? cpunext : WORK_CPU_UNBOUND; queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work); } } if (rcu_segcblist_empty(&rtpcp->cblist) || !cpu_possible(cpu)) return; raw_spin_lock_irqsave_rcu_node(rtpcp, flags); rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq)); rcu_segcblist_extract_done_cbs(&rtpcp->cblist, &rcl); raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); len = rcl.len; for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) { debug_rcu_head_callback(rhp); local_bh_disable(); rhp->func(rhp); local_bh_enable(); cond_resched(); } raw_spin_lock_irqsave_rcu_node(rtpcp, flags); rcu_segcblist_add_len(&rtpcp->cblist, -len); (void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq)); raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); } // Workqueue flood to advance callbacks and invoke any that are ready. static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp) { struct rcu_tasks *rtp; struct rcu_tasks_percpu *rtpcp = container_of(wp, struct rcu_tasks_percpu, rtp_work); rtp = rtpcp->rtpp; rcu_tasks_invoke_cbs(rtp, rtpcp); } // Wait for one grace period. static void rcu_tasks_one_gp(struct rcu_tasks *rtp, bool midboot) { int needgpcb; mutex_lock(&rtp->tasks_gp_mutex); // If there were none, wait a bit and start over. if (unlikely(midboot)) { needgpcb = 0x2; } else { mutex_unlock(&rtp->tasks_gp_mutex); set_tasks_gp_state(rtp, RTGS_WAIT_CBS); rcuwait_wait_event(&rtp->cbs_wait, (needgpcb = rcu_tasks_need_gpcb(rtp)), TASK_IDLE); mutex_lock(&rtp->tasks_gp_mutex); } if (needgpcb & 0x2) { // Wait for one grace period. set_tasks_gp_state(rtp, RTGS_WAIT_GP); rtp->gp_start = jiffies; rcu_seq_start(&rtp->tasks_gp_seq); rtp->gp_func(rtp); rcu_seq_end(&rtp->tasks_gp_seq); } // Invoke callbacks. set_tasks_gp_state(rtp, RTGS_INVOKE_CBS); rcu_tasks_invoke_cbs(rtp, per_cpu_ptr(rtp->rtpcpu, 0)); mutex_unlock(&rtp->tasks_gp_mutex); } // RCU-tasks kthread that detects grace periods and invokes callbacks. static int __noreturn rcu_tasks_kthread(void *arg) { int cpu; struct rcu_tasks *rtp = arg; for_each_possible_cpu(cpu) { struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); timer_setup(&rtpcp->lazy_timer, call_rcu_tasks_generic_timer, 0); rtpcp->urgent_gp = 1; } /* Run on housekeeping CPUs by default. Sysadm can move if desired. */ housekeeping_affine(current, HK_TYPE_RCU); smp_store_release(&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 (;;) { // Wait for one grace period and invoke any callbacks // that are ready. rcu_tasks_one_gp(rtp, false); // Paranoid sleep to keep this from entering a tight loop. schedule_timeout_idle(rtp->gp_sleep); } } // 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. */ if (WARN_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE, "synchronize_%s() called too soon", rtp->name)) return; // If the grace-period kthread is running, use it. if (READ_ONCE(rtp->kthread_ptr)) { wait_rcu_gp_state(rtp->wait_state, rtp->call_func); return; } rcu_tasks_one_gp(rtp, true); } /* 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) int rtsimc; 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); rtsimc = clamp(rcu_task_stall_info_mult, 1, 10); if (rtsimc != rcu_task_stall_info_mult) { pr_info("\tTasks-RCU CPU stall info multiplier clamped to %d (rcu_task_stall_info_mult).\n", rtsimc); rcu_task_stall_info_mult = rtsimc; } #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) { int cpu; bool havecbs = false; bool haveurgent = false; bool haveurgentcbs = false; for_each_possible_cpu(cpu) { struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); if (!data_race(rcu_segcblist_empty(&rtpcp->cblist))) havecbs = true; if (data_race(rtpcp->urgent_gp)) haveurgent = true; if (!data_race(rcu_segcblist_empty(&rtpcp->cblist)) && data_race(rtpcp->urgent_gp)) haveurgentcbs = true; if (havecbs && haveurgent && haveurgentcbs) break; } pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c%c%c l:%lu %s\n", rtp->kname, tasks_gp_state_getname(rtp), data_race(rtp->gp_state), jiffies - data_race(rtp->gp_jiffies), data_race(rcu_seq_current(&rtp->tasks_gp_seq)), data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis), ".k"[!!data_race(rtp->kthread_ptr)], ".C"[havecbs], ".u"[haveurgent], ".U"[haveurgentcbs], rtp->lazy_jiffies, 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; int fract; LIST_HEAD(holdouts); unsigned long j; unsigned long lastinfo; unsigned long lastreport; bool reported = false; int rtsi; struct task_struct *t; set_tasks_gp_state(rtp, RTGS_PRE_WAIT_GP); rtp->pregp_func(&holdouts); /* * 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); if (rtp->pertask_func) { 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; lastinfo = lastreport; rtsi = READ_ONCE(rcu_task_stall_info); // Start off with initial wait and slowly back off to 1 HZ wait. fract = rtp->init_fract; while (!list_empty(&holdouts)) { ktime_t exp; bool firstreport; bool needreport; int rtst; // Slowly back off waiting for holdouts set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS); if (!IS_ENABLED(CONFIG_PREEMPT_RT)) { schedule_timeout_idle(fract); } else { exp = jiffies_to_nsecs(fract); __set_current_state(TASK_IDLE); schedule_hrtimeout_range(&exp, jiffies_to_nsecs(HZ / 2), HRTIMER_MODE_REL_HARD); } if (fract < HZ) fract++; rtst = READ_ONCE(rcu_task_stall_timeout); needreport = rtst > 0 && time_after(jiffies, lastreport + rtst); if (needreport) { lastreport = jiffies; reported = true; } firstreport = true; WARN_ON(signal_pending(current)); set_tasks_gp_state(rtp, RTGS_SCAN_HOLDOUTS); rtp->holdouts_func(&holdouts, needreport, &firstreport); // Print pre-stall informational messages if needed. j = jiffies; if (rtsi > 0 && !reported && time_after(j, lastinfo + rtsi)) { lastinfo = j; rtsi = rtsi * rcu_task_stall_info_mult; pr_info("%s: %s grace period number %lu (since boot) is %lu jiffies old.\n", __func__, rtp->kname, rtp->tasks_gp_seq, j - rtp->gp_start); } } 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_tasks_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. // // The implementation uses rcu_tasks_wait_gp(), which relies on function // pointers in the rcu_tasks structure. The rcu_spawn_tasks_kthread() // function sets these function pointers up so that rcu_tasks_wait_gp() // invokes these functions in this order: // // rcu_tasks_pregp_step(): // Invokes synchronize_rcu() in order to wait for all in-flight // t->on_rq and t->nvcsw transitions to complete. This works because // all such transitions are carried out with interrupts disabled. // rcu_tasks_pertask(), invoked on every non-idle task: // For every runnable non-idle task other than the current one, use // get_task_struct() to pin down that task, snapshot that task's // number of voluntary context switches, and add that task to the // holdout list. // rcu_tasks_postscan(): // Gather per-CPU lists of tasks in do_exit() to ensure that all // tasks that were in the process of exiting (and which thus might // not know to synchronize with this RCU Tasks grace period) have // completed exiting. The synchronize_rcu() in rcu_tasks_postgp() // will take care of any tasks stuck in the non-preemptible region // of do_exit() following its call to exit_tasks_rcu_finish(). // check_all_holdout_tasks(), repeatedly until holdout list is empty: // Scans the holdout list, attempting to identify a quiescent state // for each task on the list. If there is a quiescent state, the // corresponding task is removed from the holdout list. // rcu_tasks_postgp(): // Invokes synchronize_rcu() in order to ensure that all prior // t->on_rq and t->nvcsw transitions are seen by all CPUs and tasks // to have happened before the end of this RCU Tasks grace period. // Again, this works because all such transitions are carried out // with interrupts disabled. // // For each exiting task, the exit_tasks_rcu_start() and // exit_tasks_rcu_finish() functions add and remove, respectively, the // current task to a per-CPU list of tasks that rcu_tasks_postscan() must // wait on. This is necessary because rcu_tasks_postscan() must wait on // tasks that have already been removed from the global list of tasks. // // Pre-grace-period update-side code is ordered before the grace // via the raw_spin_lock.*rcu_node(). Pre-grace-period read-side code // is ordered before the grace period via synchronize_rcu() call in // rcu_tasks_pregp_step() and by the scheduler's locks and interrupt // disabling. /* Pre-grace-period preparation. */ static void rcu_tasks_pregp_step(struct list_head *hop) { /* * 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(); } /* Check for quiescent states since the pregp's synchronize_rcu() */ static bool rcu_tasks_is_holdout(struct task_struct *t) { int cpu; /* Has the task been seen voluntarily sleeping? */ if (!READ_ONCE(t->on_rq)) return false; /* * Idle tasks (or idle injection) within the idle loop are RCU-tasks * quiescent states. But CPU boot code performed by the idle task * isn't a quiescent state. */ if (is_idle_task(t)) return false; cpu = task_cpu(t); /* Idle tasks on offline CPUs are RCU-tasks quiescent states. */ if (t == idle_task(cpu) && !rcu_cpu_online(cpu)) return false; return true; } /* Per-task initial processing. */ static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop) { if (t != current && rcu_tasks_is_holdout(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); } } 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"); /* Processing between scanning taskslist and draining the holdout list. */ static void rcu_tasks_postscan(struct list_head *hop) { int cpu; int rtsi = READ_ONCE(rcu_task_stall_info); if (!IS_ENABLED(CONFIG_TINY_RCU)) { tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi; add_timer(&tasks_rcu_exit_srcu_stall_timer); } /* * Exiting tasks may escape the tasklist scan. Those are vulnerable * until their final schedule() with TASK_DEAD state. To cope with * this, divide the fragile exit path part in two intersecting * read side critical sections: * * 1) A task_struct list addition before calling exit_notify(), * which may remove the task from the tasklist, with the * removal after the final preempt_disable() call in do_exit(). * * 2) An _RCU_ read side starting with the final preempt_disable() * call in do_exit() and ending with the final call to schedule() * with TASK_DEAD state. * * This handles the part 1). And postgp will handle part 2) with a * call to synchronize_rcu(). */ for_each_possible_cpu(cpu) { unsigned long j = jiffies + 1; struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rcu_tasks.rtpcpu, cpu); struct task_struct *t; struct task_struct *t1; struct list_head tmp; raw_spin_lock_irq_rcu_node(rtpcp); list_for_each_entry_safe(t, t1, &rtpcp->rtp_exit_list, rcu_tasks_exit_list) { if (list_empty(&t->rcu_tasks_holdout_list)) rcu_tasks_pertask(t, hop); // RT kernels need frequent pauses, otherwise // pause at least once per pair of jiffies. if (!IS_ENABLED(CONFIG_PREEMPT_RT) && time_before(jiffies, j)) continue; // Keep our place in the list while pausing. // Nothing else traverses this list, so adding a // bare list_head is OK. list_add(&tmp, &t->rcu_tasks_exit_list); raw_spin_unlock_irq_rcu_node(rtpcp); cond_resched(); // For CONFIG_PREEMPT=n kernels raw_spin_lock_irq_rcu_node(rtpcp); t1 = list_entry(tmp.next, struct task_struct, rcu_tasks_exit_list); list_del(&tmp); j = jiffies + 1; } raw_spin_unlock_irq_rcu_node(rtpcp); } if (!IS_ENABLED(CONFIG_TINY_RCU)) del_timer_sync(&tasks_rcu_exit_srcu_stall_timer); } /* 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) || !rcu_tasks_is_holdout(t) || (IS_ENABLED(CONFIG_NO_HZ_FULL) && !is_idle_task(t) && READ_ONCE(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, data_race(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, * enforcing the whole region before tasklist removal until * the final schedule() with TASK_DEAD state to be an RCU TASKS * read side critical section. */ synchronize_rcu(); } static void tasks_rcu_exit_srcu_stall(struct timer_list *unused) { #ifndef CONFIG_TINY_RCU int rtsi; rtsi = READ_ONCE(rcu_task_stall_info); pr_info("%s: %s grace period number %lu (since boot) gp_state: %s is %lu jiffies old.\n", __func__, rcu_tasks.kname, rcu_tasks.tasks_gp_seq, tasks_gp_state_getname(&rcu_tasks), jiffies - rcu_tasks.gp_jiffies); pr_info("Please check any exiting tasks stuck between calls to exit_tasks_rcu_start() and exit_tasks_rcu_finish()\n"); tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi; add_timer(&tasks_rcu_exit_srcu_stall_timer); #endif // #ifndef CONFIG_TINY_RCU } /** * 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_tasks_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-structure 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) { rcu_barrier_tasks_generic(&rcu_tasks); } EXPORT_SYMBOL_GPL(rcu_barrier_tasks); static int rcu_tasks_lazy_ms = -1; module_param(rcu_tasks_lazy_ms, int, 0444); static int __init rcu_spawn_tasks_kthread(void) { rcu_tasks.gp_sleep = HZ / 10; rcu_tasks.init_fract = HZ / 10; if (rcu_tasks_lazy_ms >= 0) rcu_tasks.lazy_jiffies = msecs_to_jiffies(rcu_tasks_lazy_ms); 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_tasks.wait_state = TASK_IDLE; rcu_spawn_tasks_kthread_generic(&rcu_tasks); return 0; } #if !defined(CONFIG_TINY_RCU) void show_rcu_tasks_classic_gp_kthread(void) { show_rcu_tasks_generic_gp_kthread(&rcu_tasks, ""); } EXPORT_SYMBOL_GPL(show_rcu_tasks_classic_gp_kthread); #endif // !defined(CONFIG_TINY_RCU) struct task_struct *get_rcu_tasks_gp_kthread(void) { return rcu_tasks.kthread_ptr; } EXPORT_SYMBOL_GPL(get_rcu_tasks_gp_kthread); void rcu_tasks_get_gp_data(int *flags, unsigned long *gp_seq) { *flags = 0; *gp_seq = rcu_seq_current(&rcu_tasks.tasks_gp_seq); } EXPORT_SYMBOL_GPL(rcu_tasks_get_gp_data); /* * Protect against tasklist scan blind spot while the task is exiting and * may be removed from the tasklist. Do this by adding the task to yet * another list. * * Note that the task will remove itself from this list, so there is no * need for get_task_struct(), except in the case where rcu_tasks_pertask() * adds it to the holdout list, in which case rcu_tasks_pertask() supplies * the needed get_task_struct(). */ void exit_tasks_rcu_start(void) { unsigned long flags; struct rcu_tasks_percpu *rtpcp; struct task_struct *t = current; WARN_ON_ONCE(!list_empty(&t->rcu_tasks_exit_list)); preempt_disable(); rtpcp = this_cpu_ptr(rcu_tasks.rtpcpu); t->rcu_tasks_exit_cpu = smp_processor_id(); raw_spin_lock_irqsave_rcu_node(rtpcp, flags); WARN_ON_ONCE(!rtpcp->rtp_exit_list.next); list_add(&t->rcu_tasks_exit_list, &rtpcp->rtp_exit_list); raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); preempt_enable(); } /* * Remove the task from the "yet another list" because do_exit() is now * non-preemptible, allowing synchronize_rcu() to wait beyond this point. */ void exit_tasks_rcu_finish(void) { unsigned long flags; struct rcu_tasks_percpu *rtpcp; struct task_struct *t = current; WARN_ON_ONCE(list_empty(&t->rcu_tasks_exit_list)); rtpcp = per_cpu_ptr(rcu_tasks.rtpcpu, t->rcu_tasks_exit_cpu); raw_spin_lock_irqsave_rcu_node(rtpcp, flags); list_del_init(&t->rcu_tasks_exit_list); raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); exit_tasks_rcu_finish_trace(t); } #else /* #ifdef CONFIG_TASKS_RCU */ 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_tasks_rude() API. // This invokes schedule_on_each_cpu() in order to send IPIs far and wide // and induces otherwise unnecessary context switches on all online CPUs, // whether idle or not. // // Callback handling is provided by the rcu_tasks_kthread() function. // // Ordering is provided by the scheduler's context-switch code. // 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_tasks_rcu_qs(), or transition to usermode execution (as * usermode execution is schedulable). 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-structure 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 (which is a schedulable * context), 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) { rcu_barrier_tasks_generic(&rcu_tasks_rude); } EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude); int rcu_tasks_rude_lazy_ms = -1; module_param(rcu_tasks_rude_lazy_ms, int, 0444); static int __init rcu_spawn_tasks_rude_kthread(void) { rcu_tasks_rude.gp_sleep = HZ / 10; if (rcu_tasks_rude_lazy_ms >= 0) rcu_tasks_rude.lazy_jiffies = msecs_to_jiffies(rcu_tasks_rude_lazy_ms); rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude); return 0; } #if !defined(CONFIG_TINY_RCU) void show_rcu_tasks_rude_gp_kthread(void) { show_rcu_tasks_generic_gp_kthread(&rcu_tasks_rude, ""); } EXPORT_SYMBOL_GPL(show_rcu_tasks_rude_gp_kthread); #endif // !defined(CONFIG_TINY_RCU) struct task_struct *get_rcu_tasks_rude_gp_kthread(void) { return rcu_tasks_rude.kthread_ptr; } EXPORT_SYMBOL_GPL(get_rcu_tasks_rude_gp_kthread); void rcu_tasks_rude_get_gp_data(int *flags, unsigned long *gp_seq) { *flags = 0; *gp_seq = rcu_seq_current(&rcu_tasks_rude.tasks_gp_seq); } EXPORT_SYMBOL_GPL(rcu_tasks_rude_get_gp_data); #endif /* #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 instructions, having overhead similar // to that of Preemptible RCU. // // There are of course downsides. For example, the grace-period code // can send IPIs to CPUs, even when those CPUs are in the idle loop or // in nohz_full userspace. 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 implementation uses rcu_tasks_wait_gp(), which relies on function // pointers in the rcu_tasks structure. The rcu_spawn_tasks_trace_kthread() // function sets these function pointers up so that rcu_tasks_wait_gp() // invokes these functions in this order: // // rcu_tasks_trace_pregp_step(): // Disables CPU hotplug, adds all currently executing tasks to the // holdout list, then checks the state of all tasks that blocked // or were preempted within their current RCU Tasks Trace read-side // critical section, adding them to the holdout list if appropriate. // Finally, this function re-enables CPU hotplug. // The ->pertask_func() pointer is NULL, so there is no per-task processing. // rcu_tasks_trace_postscan(): // Invokes synchronize_rcu() to wait for late-stage exiting tasks // to finish exiting. // check_all_holdout_tasks_trace(), repeatedly until holdout list is empty: // Scans the holdout list, attempting to identify a quiescent state // for each task on the list. If there is a quiescent state, the // corresponding task is removed from the holdout list. Once this // list is empty, the grace period has completed. // rcu_tasks_trace_postgp(): // Provides the needed full memory barrier and does debug checks. // // The exit_tasks_rcu_finish_trace() synchronizes with exiting tasks. // // Pre-grace-period update-side code is ordered before the grace period // via the ->cbs_lock and barriers in rcu_tasks_kthread(). Pre-grace-period // read-side code is ordered before the grace period by atomic operations // on .b.need_qs flag of each task involved in this process, or by scheduler // context-switch ordering (for locked-down non-running readers). // 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 // 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; static unsigned long n_trc_holdouts; 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"); /* Load from ->trc_reader_special.b.need_qs with proper ordering. */ static u8 rcu_ld_need_qs(struct task_struct *t) { smp_mb(); // Enforce full grace-period ordering. return smp_load_acquire(&t->trc_reader_special.b.need_qs); } /* Store to ->trc_reader_special.b.need_qs with proper ordering. */ static void rcu_st_need_qs(struct task_struct *t, u8 v) { smp_store_release(&t->trc_reader_special.b.need_qs, v); smp_mb(); // Enforce full grace-period ordering. } /* * Do a cmpxchg() on ->trc_reader_special.b.need_qs, allowing for * the four-byte operand-size restriction of some platforms. * * Returns the old value, which is often ignored. */ u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new) { union rcu_special ret; union rcu_special trs_old = READ_ONCE(t->trc_reader_special); union rcu_special trs_new = trs_old; if (trs_old.b.need_qs != old) return trs_old.b.need_qs; trs_new.b.need_qs = new; // Although cmpxchg() appears to KCSAN to update all four bytes, // only the .b.need_qs byte actually changes. instrument_atomic_read_write(&t->trc_reader_special.b.need_qs, sizeof(t->trc_reader_special.b.need_qs)); // Avoid false-positive KCSAN failures. ret.s = data_race(cmpxchg(&t->trc_reader_special.s, trs_old.s, trs_new.s)); return ret.b.need_qs; } EXPORT_SYMBOL_GPL(rcu_trc_cmpxchg_need_qs); /* * If we are the last reader, signal the grace-period kthread. * Also remove from the per-CPU list of blocked tasks. */ void rcu_read_unlock_trace_special(struct task_struct *t) { unsigned long flags; struct rcu_tasks_percpu *rtpcp; union rcu_special trs; // Open-coded full-word version of rcu_ld_need_qs(). smp_mb(); // Enforce full grace-period ordering. trs = smp_load_acquire(&t->trc_reader_special); 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 (trs.b.need_qs == (TRC_NEED_QS_CHECKED | TRC_NEED_QS)) { u8 result = rcu_trc_cmpxchg_need_qs(t, TRC_NEED_QS_CHECKED | TRC_NEED_QS, TRC_NEED_QS_CHECKED); WARN_ONCE(result != trs.b.need_qs, "%s: result = %d", __func__, result); } if (trs.b.blocked) { rtpcp = per_cpu_ptr(rcu_tasks_trace.rtpcpu, t->trc_blkd_cpu); raw_spin_lock_irqsave_rcu_node(rtpcp, flags); list_del_init(&t->trc_blkd_node); WRITE_ONCE(t->trc_reader_special.b.blocked, false); raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); } WRITE_ONCE(t->trc_reader_nesting, 0); } EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special); /* Add a newly blocked reader task to its CPU's list. */ void rcu_tasks_trace_qs_blkd(struct task_struct *t) { unsigned long flags; struct rcu_tasks_percpu *rtpcp; local_irq_save(flags); rtpcp = this_cpu_ptr(rcu_tasks_trace.rtpcpu); raw_spin_lock_rcu_node(rtpcp); // irqs already disabled t->trc_blkd_cpu = smp_processor_id(); if (!rtpcp->rtp_blkd_tasks.next) INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks); list_add(&t->trc_blkd_node, &rtpcp->rtp_blkd_tasks); WRITE_ONCE(t->trc_reader_special.b.blocked, true); raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); } EXPORT_SYMBOL_GPL(rcu_tasks_trace_qs_blkd); /* 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); n_trc_holdouts++; } } /* 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); n_trc_holdouts--; } } /* IPI handler to check task state. */ static void trc_read_check_handler(void *t_in) { int nesting; 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)) 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. nesting = READ_ONCE(t->trc_reader_nesting); if (likely(!nesting)) { rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); goto reset_ipi; } // If we are racing with an rcu_read_unlock_trace(), try again later. if (unlikely(nesting < 0)) goto reset_ipi; // Get here if the task is in a read-side critical section. // Set its state so that it will update state for the grace-period // kthread upon exit from that critical section. rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS | TRC_NEED_QS_CHECKED); 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_ptr(&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 int trc_inspect_reader(struct task_struct *t, void *bhp_in) { struct list_head *bhp = bhp_in; int cpu = task_cpu(t); int nesting; bool ofl = cpu_is_offline(cpu); if (task_curr(t) && !ofl) { // If no chance of heavyweight readers, do it the hard way. if (!IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) return -EINVAL; // 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++; // Check for "running" idle tasks on offline CPUs. if (!rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting)) return -EINVAL; // No quiescent state, do it the hard way. n_heavy_reader_updates++; nesting = 0; } else { // The task is not running, so C-language access is safe. nesting = t->trc_reader_nesting; WARN_ON_ONCE(ofl && task_curr(t) && (t != idle_task(task_cpu(t)))); if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && ofl) n_heavy_reader_ofl_updates++; } // If not exiting a read-side critical section, mark as checked // so that the grace-period kthread will remove it from the // holdout list. if (!nesting) { rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); return 0; // In QS, so done. } if (nesting < 0) return -EINVAL; // Reader transitioning, try again later. // The task is in a read-side critical section, so set up its // state so that it will update state upon exit from that critical // section. if (!rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS | TRC_NEED_QS_CHECKED)) trc_add_holdout(t, bhp); return 0; } /* 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) { rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting)); return; } // Attempt to nail down the task for inspection. get_task_struct(t); if (!task_call_func(t, trc_inspect_reader, bhp)) { put_task_struct(t); return; } put_task_struct(t); // If this task is not yet on the holdout list, then we are in // an RCU read-side critical section. Otherwise, the invocation of // trc_add_holdout() that added it to the list did the necessary // get_task_struct(). Either way, the task cannot be freed out // from under this code. // 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; 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. WARN_ONCE(1, "%s(): smp_call_function_single() failed for CPU: %d\n", __func__, cpu); rcu_tasks_trace.n_ipis_fails++; per_cpu(trc_ipi_to_cpu, cpu) = false; t->trc_ipi_to_cpu = -1; } } } /* * Initialize for first-round processing for the specified task. * Return false if task is NULL or already taken care of, true otherwise. */ static bool rcu_tasks_trace_pertask_prep(struct task_struct *t, bool notself) { // During early boot when there is only the one boot CPU, there // is no idle task for the other CPUs. Also, the grace-period // kthread is always in a quiescent state. In addition, just return // if this task is already on the list. if (unlikely(t == NULL) || (t == current && notself) || !list_empty(&t->trc_holdout_list)) return false; rcu_st_need_qs(t, 0); t->trc_ipi_to_cpu = -1; return true; } /* Do first-round processing for the specified task. */ static void rcu_tasks_trace_pertask(struct task_struct *t, struct list_head *hop) { if (rcu_tasks_trace_pertask_prep(t, true)) trc_wait_for_one_reader(t, hop); } /* Initialize for a new RCU-tasks-trace grace period. */ static void rcu_tasks_trace_pregp_step(struct list_head *hop) { LIST_HEAD(blkd_tasks); int cpu; unsigned long flags; struct rcu_tasks_percpu *rtpcp; struct task_struct *t; // 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 CPU scan for the benefit of // any IPIs that might be needed. This also waits for all readers // in CPU-hotplug code paths. cpus_read_lock(); // These rcu_tasks_trace_pertask_prep() calls are serialized to // allow safe access to the hop list. for_each_online_cpu(cpu) { rcu_read_lock(); // Note that cpu_curr_snapshot() picks up the target // CPU's current task while its runqueue is locked with // an smp_mb__after_spinlock(). This ensures that either // the grace-period kthread will see that task's read-side // critical section or the task will see the updater's pre-GP // accesses. The trailing smp_mb() in cpu_curr_snapshot() // does not currently play a role other than simplify // that function's ordering semantics. If these simplified // ordering semantics continue to be redundant, that smp_mb() // might be removed. t = cpu_curr_snapshot(cpu); if (rcu_tasks_trace_pertask_prep(t, true)) trc_add_holdout(t, hop); rcu_read_unlock(); cond_resched_tasks_rcu_qs(); } // Only after all running tasks have been accounted for is it // safe to take care of the tasks that have blocked within their // current RCU tasks trace read-side critical section. for_each_possible_cpu(cpu) { rtpcp = per_cpu_ptr(rcu_tasks_trace.rtpcpu, cpu); raw_spin_lock_irqsave_rcu_node(rtpcp, flags); list_splice_init(&rtpcp->rtp_blkd_tasks, &blkd_tasks); while (!list_empty(&blkd_tasks)) { rcu_read_lock(); t = list_first_entry(&blkd_tasks, struct task_struct, trc_blkd_node); list_del_init(&t->trc_blkd_node); list_add(&t->trc_blkd_node, &rtpcp->rtp_blkd_tasks); raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); rcu_tasks_trace_pertask(t, hop); rcu_read_unlock(); raw_spin_lock_irqsave_rcu_node(rtpcp, flags); } raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); cond_resched_tasks_rcu_qs(); } // Re-enable CPU hotplug now that the holdout list is populated. cpus_read_unlock(); } /* * Do intermediate processing between task and holdout scans. */ static void rcu_tasks_trace_postscan(struct list_head *hop) { // Wait for late-stage exiting tasks to finish exiting. // These might have passed the call to exit_tasks_rcu_finish(). // If you remove the following line, update rcu_trace_implies_rcu_gp()!!! synchronize_rcu(); // Any tasks that exit after this point will set // TRC_NEED_QS_CHECKED in ->trc_reader_special.b.need_qs. } /* Communicate task state back to the RCU tasks trace stall warning request. */ struct trc_stall_chk_rdr { int nesting; int ipi_to_cpu; u8 needqs; }; static int trc_check_slow_task(struct task_struct *t, void *arg) { struct trc_stall_chk_rdr *trc_rdrp = arg; if (task_curr(t) && cpu_online(task_cpu(t))) return false; // It is running, so decline to inspect it. trc_rdrp->nesting = READ_ONCE(t->trc_reader_nesting); trc_rdrp->ipi_to_cpu = READ_ONCE(t->trc_ipi_to_cpu); trc_rdrp->needqs = rcu_ld_need_qs(t); return true; } /* 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; struct trc_stall_chk_rdr trc_rdr; bool is_idle_tsk = is_idle_task(t); if (*firstreport) { pr_err("INFO: rcu_tasks_trace detected stalls on tasks:\n"); *firstreport = false; } cpu = task_cpu(t); if (!task_call_func(t, trc_check_slow_task, &trc_rdr)) pr_alert("P%d: %c%c\n", t->pid, ".I"[t->trc_ipi_to_cpu >= 0], ".i"[is_idle_tsk]); else pr_alert("P%d: %c%c%c%c nesting: %d%c%c cpu: %d%s\n", t->pid, ".I"[trc_rdr.ipi_to_cpu >= 0], ".i"[is_idle_tsk], ".N"[cpu >= 0 && tick_nohz_full_cpu(cpu)], ".B"[!!data_race(t->trc_reader_special.b.blocked)], trc_rdr.nesting, " !CN"[trc_rdr.needqs & 0x3], " ?"[trc_rdr.needqs > 0x3], cpu, cpu_online(cpu) ? "" : "(offline)"); 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 for IPIs. 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 && !(rcu_ld_need_qs(t) & TRC_NEED_QS_CHECKED)) trc_wait_for_one_reader(t, hop); // If check succeeded, remove this task from the list. if (smp_load_acquire(&t->trc_ipi_to_cpu) == -1 && rcu_ld_need_qs(t) == TRC_NEED_QS_CHECKED) trc_del_holdout(t); else if (needreport) show_stalled_task_trace(t, firstreport); cond_resched_tasks_rcu_qs(); } // 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(); } } static void rcu_tasks_trace_empty_fn(void *unused) { } /* Wait for grace period to complete and provide ordering. */ static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp) { int cpu; // Wait for any lingering IPI handlers to complete. Note that // if a CPU has gone offline or transitioned to userspace in the // meantime, all IPI handlers should have been drained beforehand. // Yes, this assumes that CPUs process IPIs in order. If that ever // changes, there will need to be a recheck and/or timed wait. for_each_online_cpu(cpu) if (WARN_ON_ONCE(smp_load_acquire(per_cpu_ptr(&trc_ipi_to_cpu, cpu)))) smp_call_function_single(cpu, rcu_tasks_trace_empty_fn, NULL, 1); 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) { union rcu_special trs = READ_ONCE(t->trc_reader_special); rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting)); if (WARN_ON_ONCE(rcu_ld_need_qs(t) & TRC_NEED_QS || trs.b.blocked)) rcu_read_unlock_trace_special(t); else WRITE_ONCE(t->trc_reader_nesting, 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 trace rcu-tasks * grace period elapses, in other words after all currently executing * trace rcu-tasks read-side critical sections have completed. These * read-side critical sections are delimited by calls to rcu_read_lock_trace() * and rcu_read_unlock_trace(). * * 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 * trace 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) { rcu_barrier_tasks_generic(&rcu_tasks_trace); } EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace); int rcu_tasks_trace_lazy_ms = -1; module_param(rcu_tasks_trace_lazy_ms, int, 0444); 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 = HZ / 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 / 200; if (rcu_tasks_trace.init_fract <= 0) rcu_tasks_trace.init_fract = 1; } if (rcu_tasks_trace_lazy_ms >= 0) rcu_tasks_trace.lazy_jiffies = msecs_to_jiffies(rcu_tasks_trace_lazy_ms); rcu_tasks_trace.pregp_func = rcu_tasks_trace_pregp_step; 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; } #if !defined(CONFIG_TINY_RCU) void show_rcu_tasks_trace_gp_kthread(void) { char buf[64]; snprintf(buf, sizeof(buf), "N%lu h:%lu/%lu/%lu", data_race(n_trc_holdouts), 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); } EXPORT_SYMBOL_GPL(show_rcu_tasks_trace_gp_kthread); #endif // !defined(CONFIG_TINY_RCU) struct task_struct *get_rcu_tasks_trace_gp_kthread(void) { return rcu_tasks_trace.kthread_ptr; } EXPORT_SYMBOL_GPL(get_rcu_tasks_trace_gp_kthread); void rcu_tasks_trace_get_gp_data(int *flags, unsigned long *gp_seq) { *flags = 0; *gp_seq = rcu_seq_current(&rcu_tasks_trace.tasks_gp_seq); } EXPORT_SYMBOL_GPL(rcu_tasks_trace_get_gp_data); #else /* #ifdef CONFIG_TASKS_TRACE_RCU */ static void exit_tasks_rcu_finish_trace(struct task_struct *t) { } #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 */ #ifdef CONFIG_PROVE_RCU struct rcu_tasks_test_desc { struct rcu_head rh; const char *name; bool notrun; unsigned long runstart; }; static struct rcu_tasks_test_desc tests[] = { { .name = "call_rcu_tasks()", /* If not defined, the test is skipped. */ .notrun = IS_ENABLED(CONFIG_TASKS_RCU), }, { .name = "call_rcu_tasks_rude()", /* If not defined, the test is skipped. */ .notrun = IS_ENABLED(CONFIG_TASKS_RUDE_RCU), }, { .name = "call_rcu_tasks_trace()", /* If not defined, the test is skipped. */ .notrun = IS_ENABLED(CONFIG_TASKS_TRACE_RCU) } }; static void test_rcu_tasks_callback(struct rcu_head *rhp) { struct rcu_tasks_test_desc *rttd = container_of(rhp, struct rcu_tasks_test_desc, rh); pr_info("Callback from %s invoked.\n", rttd->name); rttd->notrun = false; } static void rcu_tasks_initiate_self_tests(void) { #ifdef CONFIG_TASKS_RCU pr_info("Running RCU Tasks wait API self tests\n"); tests[0].runstart = jiffies; synchronize_rcu_tasks(); call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback); #endif #ifdef CONFIG_TASKS_RUDE_RCU pr_info("Running RCU Tasks Rude wait API self tests\n"); tests[1].runstart = jiffies; synchronize_rcu_tasks_rude(); call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback); #endif #ifdef CONFIG_TASKS_TRACE_RCU pr_info("Running RCU Tasks Trace wait API self tests\n"); tests[2].runstart = jiffies; synchronize_rcu_tasks_trace(); call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback); #endif } /* * Return: 0 - test passed * 1 - test failed, but have not timed out yet * -1 - test failed and timed out */ static int rcu_tasks_verify_self_tests(void) { int ret = 0; int i; unsigned long bst = rcu_task_stall_timeout; if (bst <= 0 || bst > RCU_TASK_BOOT_STALL_TIMEOUT) bst = RCU_TASK_BOOT_STALL_TIMEOUT; for (i = 0; i < ARRAY_SIZE(tests); i++) { while (tests[i].notrun) { // still hanging. if (time_after(jiffies, tests[i].runstart + bst)) { pr_err("%s has failed boot-time tests.\n", tests[i].name); ret = -1; break; } ret = 1; break; } } WARN_ON(ret < 0); return ret; } /* * Repeat the rcu_tasks_verify_self_tests() call once every second until the * test passes or has timed out. */ static struct delayed_work rcu_tasks_verify_work; static void rcu_tasks_verify_work_fn(struct work_struct *work __maybe_unused) { int ret = rcu_tasks_verify_self_tests(); if (ret <= 0) return; /* Test fails but not timed out yet, reschedule another check */ schedule_delayed_work(&rcu_tasks_verify_work, HZ); } static int rcu_tasks_verify_schedule_work(void) { INIT_DELAYED_WORK(&rcu_tasks_verify_work, rcu_tasks_verify_work_fn); rcu_tasks_verify_work_fn(NULL); return 0; } late_initcall(rcu_tasks_verify_schedule_work); #else /* #ifdef CONFIG_PROVE_RCU */ static void rcu_tasks_initiate_self_tests(void) { } #endif /* #else #ifdef CONFIG_PROVE_RCU */ void __init tasks_cblist_init_generic(void) { lockdep_assert_irqs_disabled(); WARN_ON(num_online_cpus() > 1); #ifdef CONFIG_TASKS_RCU cblist_init_generic(&rcu_tasks); #endif #ifdef CONFIG_TASKS_RUDE_RCU cblist_init_generic(&rcu_tasks_rude); #endif #ifdef CONFIG_TASKS_TRACE_RCU cblist_init_generic(&rcu_tasks_trace); #endif } 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 // Run the self-tests. rcu_tasks_initiate_self_tests(); } #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ static inline void rcu_tasks_bootup_oddness(void) {} #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
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