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d6ad60635c
The RCU Tasks Trace grace-period kthread loops across all CPUs, and there can be quite a few CPUs, with some commercially available systems sporting well over a thousand of them. Some of these loops can feature IPIs, which can take some time. This commit therefore places a call to cond_resched_tasks_rcu_qs() in each such loop. Link: https://docs.google.com/document/d/1V0YnG1HTWMt9WHJjroiJL9lf-hMrud4v8Fn3fhyY0cI/edit?usp=sharing Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
1915 lines
64 KiB
C
1915 lines
64 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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* Task-based RCU implementations.
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*
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* Copyright (C) 2020 Paul E. McKenney
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*/
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#ifdef CONFIG_TASKS_RCU_GENERIC
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#include "rcu_segcblist.h"
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////////////////////////////////////////////////////////////////////////
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//
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// Generic data structures.
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struct rcu_tasks;
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typedef void (*rcu_tasks_gp_func_t)(struct rcu_tasks *rtp);
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typedef void (*pregp_func_t)(struct list_head *hop);
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typedef void (*pertask_func_t)(struct task_struct *t, struct list_head *hop);
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typedef void (*postscan_func_t)(struct list_head *hop);
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typedef void (*holdouts_func_t)(struct list_head *hop, bool ndrpt, bool *frptp);
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typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
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/**
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* struct rcu_tasks_percpu - Per-CPU component of definition for a Tasks-RCU-like mechanism.
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* @cblist: Callback list.
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* @lock: Lock protecting per-CPU callback list.
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* @rtp_jiffies: Jiffies counter value for statistics.
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* @rtp_n_lock_retries: Rough lock-contention statistic.
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* @rtp_work: Work queue for invoking callbacks.
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* @rtp_irq_work: IRQ work queue for deferred wakeups.
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* @barrier_q_head: RCU callback for barrier operation.
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* @rtp_blkd_tasks: List of tasks blocked as readers.
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* @cpu: CPU number corresponding to this entry.
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* @rtpp: Pointer to the rcu_tasks structure.
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*/
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struct rcu_tasks_percpu {
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struct rcu_segcblist cblist;
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raw_spinlock_t __private lock;
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unsigned long rtp_jiffies;
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unsigned long rtp_n_lock_retries;
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struct work_struct rtp_work;
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struct irq_work rtp_irq_work;
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struct rcu_head barrier_q_head;
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struct list_head rtp_blkd_tasks;
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int cpu;
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struct rcu_tasks *rtpp;
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};
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/**
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* struct rcu_tasks - Definition for a Tasks-RCU-like mechanism.
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* @cbs_wait: RCU wait allowing a new callback to get kthread's attention.
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* @cbs_gbl_lock: Lock protecting callback list.
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* @tasks_gp_mutex: Mutex protecting grace period, needed during mid-boot dead zone.
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* @kthread_ptr: This flavor's grace-period/callback-invocation kthread.
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* @gp_func: This flavor's grace-period-wait function.
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* @gp_state: Grace period's most recent state transition (debugging).
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* @gp_sleep: Per-grace-period sleep to prevent CPU-bound looping.
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* @init_fract: Initial backoff sleep interval.
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* @gp_jiffies: Time of last @gp_state transition.
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* @gp_start: Most recent grace-period start in jiffies.
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* @tasks_gp_seq: Number of grace periods completed since boot.
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* @n_ipis: Number of IPIs sent to encourage grace periods to end.
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* @n_ipis_fails: Number of IPI-send failures.
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* @pregp_func: This flavor's pre-grace-period function (optional).
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* @pertask_func: This flavor's per-task scan function (optional).
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* @postscan_func: This flavor's post-task scan function (optional).
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* @holdouts_func: This flavor's holdout-list scan function (optional).
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* @postgp_func: This flavor's post-grace-period function (optional).
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* @call_func: This flavor's call_rcu()-equivalent function.
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* @rtpcpu: This flavor's rcu_tasks_percpu structure.
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* @percpu_enqueue_shift: Shift down CPU ID this much when enqueuing callbacks.
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* @percpu_enqueue_lim: Number of per-CPU callback queues in use for enqueuing.
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* @percpu_dequeue_lim: Number of per-CPU callback queues in use for dequeuing.
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* @percpu_dequeue_gpseq: RCU grace-period number to propagate enqueue limit to dequeuers.
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* @barrier_q_mutex: Serialize barrier operations.
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* @barrier_q_count: Number of queues being waited on.
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* @barrier_q_completion: Barrier wait/wakeup mechanism.
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* @barrier_q_seq: Sequence number for barrier operations.
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* @name: This flavor's textual name.
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* @kname: This flavor's kthread name.
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*/
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struct rcu_tasks {
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struct rcuwait cbs_wait;
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raw_spinlock_t cbs_gbl_lock;
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struct mutex tasks_gp_mutex;
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int gp_state;
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int gp_sleep;
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int init_fract;
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unsigned long gp_jiffies;
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unsigned long gp_start;
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unsigned long tasks_gp_seq;
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unsigned long n_ipis;
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unsigned long n_ipis_fails;
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struct task_struct *kthread_ptr;
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rcu_tasks_gp_func_t gp_func;
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pregp_func_t pregp_func;
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pertask_func_t pertask_func;
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postscan_func_t postscan_func;
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holdouts_func_t holdouts_func;
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postgp_func_t postgp_func;
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call_rcu_func_t call_func;
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struct rcu_tasks_percpu __percpu *rtpcpu;
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int percpu_enqueue_shift;
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int percpu_enqueue_lim;
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int percpu_dequeue_lim;
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unsigned long percpu_dequeue_gpseq;
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struct mutex barrier_q_mutex;
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atomic_t barrier_q_count;
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struct completion barrier_q_completion;
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unsigned long barrier_q_seq;
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char *name;
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char *kname;
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};
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static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp);
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#define DEFINE_RCU_TASKS(rt_name, gp, call, n) \
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static DEFINE_PER_CPU(struct rcu_tasks_percpu, rt_name ## __percpu) = { \
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.lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name ## __percpu.cbs_pcpu_lock), \
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.rtp_irq_work = IRQ_WORK_INIT_HARD(call_rcu_tasks_iw_wakeup), \
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}; \
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static struct rcu_tasks rt_name = \
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{ \
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.cbs_wait = __RCUWAIT_INITIALIZER(rt_name.wait), \
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.cbs_gbl_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_gbl_lock), \
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.tasks_gp_mutex = __MUTEX_INITIALIZER(rt_name.tasks_gp_mutex), \
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.gp_func = gp, \
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.call_func = call, \
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.rtpcpu = &rt_name ## __percpu, \
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.name = n, \
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.percpu_enqueue_shift = order_base_2(CONFIG_NR_CPUS), \
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.percpu_enqueue_lim = 1, \
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.percpu_dequeue_lim = 1, \
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.barrier_q_mutex = __MUTEX_INITIALIZER(rt_name.barrier_q_mutex), \
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.barrier_q_seq = (0UL - 50UL) << RCU_SEQ_CTR_SHIFT, \
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.kname = #rt_name, \
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}
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/* Track exiting tasks in order to allow them to be waited for. */
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DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
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/* Avoid IPIing CPUs early in the grace period. */
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#define RCU_TASK_IPI_DELAY (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) ? HZ / 2 : 0)
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static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY;
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module_param(rcu_task_ipi_delay, int, 0644);
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/* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */
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#define RCU_TASK_BOOT_STALL_TIMEOUT (HZ * 30)
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#define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10)
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static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
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module_param(rcu_task_stall_timeout, int, 0644);
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#define RCU_TASK_STALL_INFO (HZ * 10)
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static int rcu_task_stall_info __read_mostly = RCU_TASK_STALL_INFO;
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module_param(rcu_task_stall_info, int, 0644);
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static int rcu_task_stall_info_mult __read_mostly = 3;
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module_param(rcu_task_stall_info_mult, int, 0444);
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static int rcu_task_enqueue_lim __read_mostly = -1;
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module_param(rcu_task_enqueue_lim, int, 0444);
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static bool rcu_task_cb_adjust;
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static int rcu_task_contend_lim __read_mostly = 100;
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module_param(rcu_task_contend_lim, int, 0444);
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static int rcu_task_collapse_lim __read_mostly = 10;
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module_param(rcu_task_collapse_lim, int, 0444);
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/* RCU tasks grace-period state for debugging. */
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#define RTGS_INIT 0
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#define RTGS_WAIT_WAIT_CBS 1
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#define RTGS_WAIT_GP 2
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#define RTGS_PRE_WAIT_GP 3
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#define RTGS_SCAN_TASKLIST 4
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#define RTGS_POST_SCAN_TASKLIST 5
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#define RTGS_WAIT_SCAN_HOLDOUTS 6
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#define RTGS_SCAN_HOLDOUTS 7
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#define RTGS_POST_GP 8
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#define RTGS_WAIT_READERS 9
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#define RTGS_INVOKE_CBS 10
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#define RTGS_WAIT_CBS 11
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#ifndef CONFIG_TINY_RCU
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static const char * const rcu_tasks_gp_state_names[] = {
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"RTGS_INIT",
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"RTGS_WAIT_WAIT_CBS",
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"RTGS_WAIT_GP",
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"RTGS_PRE_WAIT_GP",
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"RTGS_SCAN_TASKLIST",
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"RTGS_POST_SCAN_TASKLIST",
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"RTGS_WAIT_SCAN_HOLDOUTS",
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"RTGS_SCAN_HOLDOUTS",
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"RTGS_POST_GP",
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"RTGS_WAIT_READERS",
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"RTGS_INVOKE_CBS",
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"RTGS_WAIT_CBS",
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};
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#endif /* #ifndef CONFIG_TINY_RCU */
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////////////////////////////////////////////////////////////////////////
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//
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// Generic code.
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static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp);
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/* Record grace-period phase and time. */
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static void set_tasks_gp_state(struct rcu_tasks *rtp, int newstate)
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{
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rtp->gp_state = newstate;
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rtp->gp_jiffies = jiffies;
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}
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#ifndef CONFIG_TINY_RCU
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/* Return state name. */
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static const char *tasks_gp_state_getname(struct rcu_tasks *rtp)
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{
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int i = data_race(rtp->gp_state); // Let KCSAN detect update races
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int j = READ_ONCE(i); // Prevent the compiler from reading twice
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if (j >= ARRAY_SIZE(rcu_tasks_gp_state_names))
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return "???";
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return rcu_tasks_gp_state_names[j];
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}
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#endif /* #ifndef CONFIG_TINY_RCU */
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// Initialize per-CPU callback lists for the specified flavor of
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// Tasks RCU.
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static void cblist_init_generic(struct rcu_tasks *rtp)
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{
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int cpu;
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unsigned long flags;
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int lim;
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int shift;
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raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
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if (rcu_task_enqueue_lim < 0) {
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rcu_task_enqueue_lim = 1;
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rcu_task_cb_adjust = true;
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pr_info("%s: Setting adjustable number of callback queues.\n", __func__);
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} else if (rcu_task_enqueue_lim == 0) {
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rcu_task_enqueue_lim = 1;
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}
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lim = rcu_task_enqueue_lim;
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if (lim > nr_cpu_ids)
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lim = nr_cpu_ids;
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shift = ilog2(nr_cpu_ids / lim);
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if (((nr_cpu_ids - 1) >> shift) >= lim)
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shift++;
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WRITE_ONCE(rtp->percpu_enqueue_shift, shift);
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WRITE_ONCE(rtp->percpu_dequeue_lim, lim);
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smp_store_release(&rtp->percpu_enqueue_lim, lim);
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for_each_possible_cpu(cpu) {
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struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
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WARN_ON_ONCE(!rtpcp);
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if (cpu)
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raw_spin_lock_init(&ACCESS_PRIVATE(rtpcp, lock));
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raw_spin_lock_rcu_node(rtpcp); // irqs already disabled.
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if (rcu_segcblist_empty(&rtpcp->cblist))
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rcu_segcblist_init(&rtpcp->cblist);
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INIT_WORK(&rtpcp->rtp_work, rcu_tasks_invoke_cbs_wq);
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rtpcp->cpu = cpu;
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rtpcp->rtpp = rtp;
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if (!rtpcp->rtp_blkd_tasks.next)
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INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks);
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raw_spin_unlock_rcu_node(rtpcp); // irqs remain disabled.
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}
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raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
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pr_info("%s: Setting shift to %d and lim to %d.\n", __func__, data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim));
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}
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// IRQ-work handler that does deferred wakeup for call_rcu_tasks_generic().
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static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp)
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{
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struct rcu_tasks *rtp;
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struct rcu_tasks_percpu *rtpcp = container_of(iwp, struct rcu_tasks_percpu, rtp_irq_work);
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rtp = rtpcp->rtpp;
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rcuwait_wake_up(&rtp->cbs_wait);
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}
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// Enqueue a callback for the specified flavor of Tasks RCU.
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static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
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struct rcu_tasks *rtp)
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{
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int chosen_cpu;
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unsigned long flags;
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int ideal_cpu;
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unsigned long j;
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bool needadjust = false;
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bool needwake;
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struct rcu_tasks_percpu *rtpcp;
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rhp->next = NULL;
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rhp->func = func;
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local_irq_save(flags);
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rcu_read_lock();
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ideal_cpu = smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift);
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chosen_cpu = cpumask_next(ideal_cpu - 1, cpu_possible_mask);
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rtpcp = per_cpu_ptr(rtp->rtpcpu, chosen_cpu);
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if (!raw_spin_trylock_rcu_node(rtpcp)) { // irqs already disabled.
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raw_spin_lock_rcu_node(rtpcp); // irqs already disabled.
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j = jiffies;
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if (rtpcp->rtp_jiffies != j) {
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rtpcp->rtp_jiffies = j;
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rtpcp->rtp_n_lock_retries = 0;
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}
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if (rcu_task_cb_adjust && ++rtpcp->rtp_n_lock_retries > rcu_task_contend_lim &&
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READ_ONCE(rtp->percpu_enqueue_lim) != nr_cpu_ids)
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needadjust = true; // Defer adjustment to avoid deadlock.
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}
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if (!rcu_segcblist_is_enabled(&rtpcp->cblist)) {
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raw_spin_unlock_rcu_node(rtpcp); // irqs remain disabled.
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cblist_init_generic(rtp);
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raw_spin_lock_rcu_node(rtpcp); // irqs already disabled.
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}
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needwake = rcu_segcblist_empty(&rtpcp->cblist);
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rcu_segcblist_enqueue(&rtpcp->cblist, rhp);
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raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
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if (unlikely(needadjust)) {
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raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
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if (rtp->percpu_enqueue_lim != nr_cpu_ids) {
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WRITE_ONCE(rtp->percpu_enqueue_shift, 0);
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WRITE_ONCE(rtp->percpu_dequeue_lim, nr_cpu_ids);
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smp_store_release(&rtp->percpu_enqueue_lim, nr_cpu_ids);
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pr_info("Switching %s to per-CPU callback queuing.\n", rtp->name);
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}
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raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
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}
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rcu_read_unlock();
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/* We can't create the thread unless interrupts are enabled. */
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if (needwake && READ_ONCE(rtp->kthread_ptr))
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irq_work_queue(&rtpcp->rtp_irq_work);
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}
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// RCU callback function for rcu_barrier_tasks_generic().
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static void rcu_barrier_tasks_generic_cb(struct rcu_head *rhp)
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{
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struct rcu_tasks *rtp;
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struct rcu_tasks_percpu *rtpcp;
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rtpcp = container_of(rhp, struct rcu_tasks_percpu, barrier_q_head);
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rtp = rtpcp->rtpp;
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if (atomic_dec_and_test(&rtp->barrier_q_count))
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complete(&rtp->barrier_q_completion);
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}
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// Wait for all in-flight callbacks for the specified RCU Tasks flavor.
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// Operates in a manner similar to rcu_barrier().
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static void rcu_barrier_tasks_generic(struct rcu_tasks *rtp)
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{
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int cpu;
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unsigned long flags;
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struct rcu_tasks_percpu *rtpcp;
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unsigned long s = rcu_seq_snap(&rtp->barrier_q_seq);
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mutex_lock(&rtp->barrier_q_mutex);
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if (rcu_seq_done(&rtp->barrier_q_seq, s)) {
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smp_mb();
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mutex_unlock(&rtp->barrier_q_mutex);
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return;
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}
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rcu_seq_start(&rtp->barrier_q_seq);
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init_completion(&rtp->barrier_q_completion);
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atomic_set(&rtp->barrier_q_count, 2);
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for_each_possible_cpu(cpu) {
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if (cpu >= smp_load_acquire(&rtp->percpu_dequeue_lim))
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break;
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rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
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rtpcp->barrier_q_head.func = rcu_barrier_tasks_generic_cb;
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raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
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if (rcu_segcblist_entrain(&rtpcp->cblist, &rtpcp->barrier_q_head))
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atomic_inc(&rtp->barrier_q_count);
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raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
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}
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if (atomic_sub_and_test(2, &rtp->barrier_q_count))
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complete(&rtp->barrier_q_completion);
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wait_for_completion(&rtp->barrier_q_completion);
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rcu_seq_end(&rtp->barrier_q_seq);
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mutex_unlock(&rtp->barrier_q_mutex);
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}
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// Advance callbacks and indicate whether either a grace period or
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// callback invocation is needed.
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static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
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{
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int cpu;
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unsigned long flags;
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long n;
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long ncbs = 0;
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long ncbsnz = 0;
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int needgpcb = 0;
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for (cpu = 0; cpu < smp_load_acquire(&rtp->percpu_dequeue_lim); cpu++) {
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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 (rcu_segcblist_pend_cbs(&rtpcp->cblist))
|
|
needgpcb |= 0x3;
|
|
if (!rcu_segcblist_empty(&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();
|
|
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 &&
|
|
poll_state_synchronize_rcu(rtp->percpu_dequeue_gpseq)) {
|
|
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);
|
|
}
|
|
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;
|
|
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);
|
|
queue_work_on(cpunext, system_wq, &rtpcp_next->rtp_work);
|
|
cpunext++;
|
|
if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) {
|
|
rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext);
|
|
queue_work_on(cpunext, 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)) {
|
|
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 {
|
|
set_tasks_gp_state(rtp, RTGS_WAIT_CBS);
|
|
rcuwait_wait_event(&rtp->cbs_wait,
|
|
(needgpcb = rcu_tasks_need_gpcb(rtp)),
|
|
TASK_IDLE);
|
|
}
|
|
|
|
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)
|
|
{
|
|
struct rcu_tasks *rtp = arg;
|
|
|
|
/* Run on housekeeping CPUs by default. Sysadm can move if desired. */
|
|
housekeeping_affine(current, HK_TYPE_RCU);
|
|
WRITE_ONCE(rtp->kthread_ptr, current); // Let GPs start!
|
|
|
|
/*
|
|
* Each pass through the following loop makes one check for
|
|
* newly arrived callbacks, and, if there are some, waits for
|
|
* one RCU-tasks grace period and then invokes the callbacks.
|
|
* This loop is terminated by the system going down. ;-)
|
|
*/
|
|
for (;;) {
|
|
// 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. */
|
|
WARN_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
|
|
"synchronize_rcu_tasks called too soon");
|
|
|
|
// If the grace-period kthread is running, use it.
|
|
if (READ_ONCE(rtp->kthread_ptr)) {
|
|
wait_rcu_gp(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;
|
|
|
|
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;
|
|
break;
|
|
}
|
|
}
|
|
pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c %s\n",
|
|
rtp->kname,
|
|
tasks_gp_state_getname(rtp), data_race(rtp->gp_state),
|
|
jiffies - data_race(rtp->gp_jiffies),
|
|
data_race(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],
|
|
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 %lu 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():
|
|
// Invoke synchronize_srcu() 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.
|
|
// 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 begin and end, respectively, the SRCU
|
|
// read-side critical sections waited for by rcu_tasks_postscan().
|
|
//
|
|
// 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();
|
|
}
|
|
|
|
/* Per-task initial processing. */
|
|
static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop)
|
|
{
|
|
if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) {
|
|
get_task_struct(t);
|
|
t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
|
|
WRITE_ONCE(t->rcu_tasks_holdout, true);
|
|
list_add(&t->rcu_tasks_holdout_list, hop);
|
|
}
|
|
}
|
|
|
|
/* Processing between scanning taskslist and draining the holdout list. */
|
|
static void rcu_tasks_postscan(struct list_head *hop)
|
|
{
|
|
/*
|
|
* Wait for tasks that are in the process of exiting. This
|
|
* does only part of the job, ensuring that all tasks that were
|
|
* previously exiting reach the point where they have disabled
|
|
* preemption, allowing the later synchronize_rcu() to finish
|
|
* the job.
|
|
*/
|
|
synchronize_srcu(&tasks_rcu_exit_srcu);
|
|
}
|
|
|
|
/* See if tasks are still holding out, complain if so. */
|
|
static void check_holdout_task(struct task_struct *t,
|
|
bool needreport, bool *firstreport)
|
|
{
|
|
int cpu;
|
|
|
|
if (!READ_ONCE(t->rcu_tasks_holdout) ||
|
|
t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
|
|
!READ_ONCE(t->on_rq) ||
|
|
(IS_ENABLED(CONFIG_NO_HZ_FULL) &&
|
|
!is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
|
|
WRITE_ONCE(t->rcu_tasks_holdout, false);
|
|
list_del_init(&t->rcu_tasks_holdout_list);
|
|
put_task_struct(t);
|
|
return;
|
|
}
|
|
rcu_request_urgent_qs_task(t);
|
|
if (!needreport)
|
|
return;
|
|
if (*firstreport) {
|
|
pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
|
|
*firstreport = false;
|
|
}
|
|
cpu = task_cpu(t);
|
|
pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
|
|
t, ".I"[is_idle_task(t)],
|
|
"N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
|
|
t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
|
|
t->rcu_tasks_idle_cpu, cpu);
|
|
sched_show_task(t);
|
|
}
|
|
|
|
/* Scan the holdout lists for tasks no longer holding out. */
|
|
static void check_all_holdout_tasks(struct list_head *hop,
|
|
bool needreport, bool *firstreport)
|
|
{
|
|
struct task_struct *t, *t1;
|
|
|
|
list_for_each_entry_safe(t, t1, hop, rcu_tasks_holdout_list) {
|
|
check_holdout_task(t, needreport, firstreport);
|
|
cond_resched();
|
|
}
|
|
}
|
|
|
|
/* Finish off the Tasks-RCU grace period. */
|
|
static void rcu_tasks_postgp(struct rcu_tasks *rtp)
|
|
{
|
|
/*
|
|
* Because ->on_rq and ->nvcsw are not guaranteed to have a full
|
|
* memory barriers prior to them in the schedule() path, memory
|
|
* reordering on other CPUs could cause their RCU-tasks read-side
|
|
* critical sections to extend past the end of the grace period.
|
|
* However, because these ->nvcsw updates are carried out with
|
|
* interrupts disabled, we can use synchronize_rcu() to force the
|
|
* needed ordering on all such CPUs.
|
|
*
|
|
* This synchronize_rcu() also confines all ->rcu_tasks_holdout
|
|
* accesses to be within the grace period, avoiding the need for
|
|
* memory barriers for ->rcu_tasks_holdout accesses.
|
|
*
|
|
* In addition, this synchronize_rcu() waits for exiting tasks
|
|
* to complete their final preempt_disable() region of execution,
|
|
* cleaning up after the synchronize_srcu() above.
|
|
*/
|
|
synchronize_rcu();
|
|
}
|
|
|
|
void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func);
|
|
DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks");
|
|
|
|
/**
|
|
* call_rcu_tasks() - Queue an RCU for invocation task-based grace period
|
|
* @rhp: structure to be used for queueing the RCU updates.
|
|
* @func: actual callback function to be invoked after the grace period
|
|
*
|
|
* The callback function will be invoked some time after a full grace
|
|
* period elapses, in other words after all currently executing RCU
|
|
* read-side critical sections have completed. call_rcu_tasks() assumes
|
|
* that the read-side critical sections end at a voluntary context
|
|
* switch (not a preemption!), cond_resched_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 __init rcu_spawn_tasks_kthread(void)
|
|
{
|
|
cblist_init_generic(&rcu_tasks);
|
|
rcu_tasks.gp_sleep = HZ / 10;
|
|
rcu_tasks.init_fract = HZ / 10;
|
|
rcu_tasks.pregp_func = rcu_tasks_pregp_step;
|
|
rcu_tasks.pertask_func = rcu_tasks_pertask;
|
|
rcu_tasks.postscan_func = rcu_tasks_postscan;
|
|
rcu_tasks.holdouts_func = check_all_holdout_tasks;
|
|
rcu_tasks.postgp_func = rcu_tasks_postgp;
|
|
rcu_spawn_tasks_kthread_generic(&rcu_tasks);
|
|
return 0;
|
|
}
|
|
|
|
#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)
|
|
|
|
/* Do the srcu_read_lock() for the above synchronize_srcu(). */
|
|
void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
|
|
{
|
|
preempt_disable();
|
|
current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
|
|
preempt_enable();
|
|
}
|
|
|
|
/* Do the srcu_read_unlock() for the above synchronize_srcu(). */
|
|
void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
preempt_disable();
|
|
__srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx);
|
|
preempt_enable();
|
|
exit_tasks_rcu_finish_trace(t);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_TASKS_RCU */
|
|
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)
|
|
{
|
|
if (num_online_cpus() <= 1)
|
|
return; // Fastpath for only one CPU.
|
|
|
|
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);
|
|
|
|
static int __init rcu_spawn_tasks_rude_kthread(void)
|
|
{
|
|
cblist_init_generic(&rcu_tasks_rude);
|
|
rcu_tasks_rude.gp_sleep = HZ / 10;
|
|
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)
|
|
#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;
|
|
ret.s = 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) && !is_idle_task(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();
|
|
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().
|
|
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);
|
|
|
|
static int __init rcu_spawn_tasks_trace_kthread(void)
|
|
{
|
|
cblist_init_generic(&rcu_tasks_trace);
|
|
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;
|
|
}
|
|
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];
|
|
|
|
sprintf(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)
|
|
|
|
#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)
|
|
{
|
|
unsigned long j = jiffies;
|
|
|
|
pr_info("Running RCU-tasks wait API self tests\n");
|
|
#ifdef CONFIG_TASKS_RCU
|
|
tests[0].runstart = j;
|
|
synchronize_rcu_tasks();
|
|
call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
|
|
#endif
|
|
|
|
#ifdef CONFIG_TASKS_RUDE_RCU
|
|
tests[1].runstart = j;
|
|
synchronize_rcu_tasks_rude();
|
|
call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback);
|
|
#endif
|
|
|
|
#ifdef CONFIG_TASKS_TRACE_RCU
|
|
tests[2].runstart = j;
|
|
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 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 */
|