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dfcb275402
The kernel/rcu/tree_plugin.h file contains not only the plugins for preemptible RCU, but also many other features including rcu_nocbs callback offloading. This offloading has become large and complex, so it is time to put it in its own file. This commit starts that process. Suggested-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> [ paulmck: Rename to tree_nocb.h, add Frederic as author. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
1497 lines
45 KiB
C
1497 lines
45 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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* Read-Copy Update mechanism for mutual exclusion (tree-based version)
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* Internal non-public definitions that provide either classic
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* or preemptible semantics.
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*
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* Copyright Red Hat, 2009
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* Copyright IBM Corporation, 2009
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* Copyright SUSE, 2021
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*
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* Author: Ingo Molnar <mingo@elte.hu>
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* Paul E. McKenney <paulmck@linux.ibm.com>
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* Frederic Weisbecker <frederic@kernel.org>
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*/
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#ifdef CONFIG_RCU_NOCB_CPU
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static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
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static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
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static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp)
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{
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return lockdep_is_held(&rdp->nocb_lock);
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}
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static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp)
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{
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/* Race on early boot between thread creation and assignment */
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if (!rdp->nocb_cb_kthread || !rdp->nocb_gp_kthread)
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return true;
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if (current == rdp->nocb_cb_kthread || current == rdp->nocb_gp_kthread)
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if (in_task())
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return true;
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return false;
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}
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/*
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* Offload callback processing from the boot-time-specified set of CPUs
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* specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
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* created that pull the callbacks from the corresponding CPU, wait for
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* a grace period to elapse, and invoke the callbacks. These kthreads
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* are organized into GP kthreads, which manage incoming callbacks, wait for
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* grace periods, and awaken CB kthreads, and the CB kthreads, which only
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* invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
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* do a wake_up() on their GP kthread when they insert a callback into any
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* empty list, unless the rcu_nocb_poll boot parameter has been specified,
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* in which case each kthread actively polls its CPU. (Which isn't so great
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* for energy efficiency, but which does reduce RCU's overhead on that CPU.)
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*
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* This is intended to be used in conjunction with Frederic Weisbecker's
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* adaptive-idle work, which would seriously reduce OS jitter on CPUs
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* running CPU-bound user-mode computations.
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*
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* Offloading of callbacks can also be used as an energy-efficiency
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* measure because CPUs with no RCU callbacks queued are more aggressive
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* about entering dyntick-idle mode.
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*/
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/*
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* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
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* If the list is invalid, a warning is emitted and all CPUs are offloaded.
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*/
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static int __init rcu_nocb_setup(char *str)
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{
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alloc_bootmem_cpumask_var(&rcu_nocb_mask);
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if (cpulist_parse(str, rcu_nocb_mask)) {
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pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
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cpumask_setall(rcu_nocb_mask);
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}
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return 1;
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}
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__setup("rcu_nocbs=", rcu_nocb_setup);
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static int __init parse_rcu_nocb_poll(char *arg)
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{
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rcu_nocb_poll = true;
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return 0;
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}
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early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
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/*
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* Don't bother bypassing ->cblist if the call_rcu() rate is low.
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* After all, the main point of bypassing is to avoid lock contention
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* on ->nocb_lock, which only can happen at high call_rcu() rates.
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*/
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static int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ;
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module_param(nocb_nobypass_lim_per_jiffy, int, 0);
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/*
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* Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the
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* lock isn't immediately available, increment ->nocb_lock_contended to
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* flag the contention.
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*/
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static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
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__acquires(&rdp->nocb_bypass_lock)
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{
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lockdep_assert_irqs_disabled();
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if (raw_spin_trylock(&rdp->nocb_bypass_lock))
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return;
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atomic_inc(&rdp->nocb_lock_contended);
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WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
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smp_mb__after_atomic(); /* atomic_inc() before lock. */
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raw_spin_lock(&rdp->nocb_bypass_lock);
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smp_mb__before_atomic(); /* atomic_dec() after lock. */
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atomic_dec(&rdp->nocb_lock_contended);
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}
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/*
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* Spinwait until the specified rcu_data structure's ->nocb_lock is
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* not contended. Please note that this is extremely special-purpose,
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* relying on the fact that at most two kthreads and one CPU contend for
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* this lock, and also that the two kthreads are guaranteed to have frequent
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* grace-period-duration time intervals between successive acquisitions
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* of the lock. This allows us to use an extremely simple throttling
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* mechanism, and further to apply it only to the CPU doing floods of
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* call_rcu() invocations. Don't try this at home!
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*/
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static void rcu_nocb_wait_contended(struct rcu_data *rdp)
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{
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WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
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while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)))
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cpu_relax();
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}
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/*
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* Conditionally acquire the specified rcu_data structure's
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* ->nocb_bypass_lock.
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*/
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static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp)
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{
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lockdep_assert_irqs_disabled();
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return raw_spin_trylock(&rdp->nocb_bypass_lock);
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}
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/*
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* Release the specified rcu_data structure's ->nocb_bypass_lock.
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*/
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static void rcu_nocb_bypass_unlock(struct rcu_data *rdp)
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__releases(&rdp->nocb_bypass_lock)
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{
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lockdep_assert_irqs_disabled();
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raw_spin_unlock(&rdp->nocb_bypass_lock);
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}
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/*
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* Acquire the specified rcu_data structure's ->nocb_lock, but only
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* if it corresponds to a no-CBs CPU.
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*/
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static void rcu_nocb_lock(struct rcu_data *rdp)
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{
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lockdep_assert_irqs_disabled();
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if (!rcu_rdp_is_offloaded(rdp))
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return;
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raw_spin_lock(&rdp->nocb_lock);
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}
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/*
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* Release the specified rcu_data structure's ->nocb_lock, but only
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* if it corresponds to a no-CBs CPU.
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*/
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static void rcu_nocb_unlock(struct rcu_data *rdp)
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{
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if (rcu_rdp_is_offloaded(rdp)) {
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lockdep_assert_irqs_disabled();
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raw_spin_unlock(&rdp->nocb_lock);
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}
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}
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/*
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* Release the specified rcu_data structure's ->nocb_lock and restore
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* interrupts, but only if it corresponds to a no-CBs CPU.
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*/
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static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
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unsigned long flags)
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{
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if (rcu_rdp_is_offloaded(rdp)) {
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lockdep_assert_irqs_disabled();
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raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
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} else {
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local_irq_restore(flags);
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}
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}
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/* Lockdep check that ->cblist may be safely accessed. */
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static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
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{
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lockdep_assert_irqs_disabled();
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if (rcu_rdp_is_offloaded(rdp))
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lockdep_assert_held(&rdp->nocb_lock);
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}
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/*
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* Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
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* grace period.
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*/
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static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
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{
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swake_up_all(sq);
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}
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static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
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{
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return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1];
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}
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static void rcu_init_one_nocb(struct rcu_node *rnp)
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{
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init_swait_queue_head(&rnp->nocb_gp_wq[0]);
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init_swait_queue_head(&rnp->nocb_gp_wq[1]);
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}
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/* Is the specified CPU a no-CBs CPU? */
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bool rcu_is_nocb_cpu(int cpu)
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{
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if (cpumask_available(rcu_nocb_mask))
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return cpumask_test_cpu(cpu, rcu_nocb_mask);
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return false;
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}
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static bool __wake_nocb_gp(struct rcu_data *rdp_gp,
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struct rcu_data *rdp,
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bool force, unsigned long flags)
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__releases(rdp_gp->nocb_gp_lock)
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{
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bool needwake = false;
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if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) {
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raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
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trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
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TPS("AlreadyAwake"));
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return false;
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}
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if (rdp_gp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
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WRITE_ONCE(rdp_gp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
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del_timer(&rdp_gp->nocb_timer);
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}
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if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) {
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WRITE_ONCE(rdp_gp->nocb_gp_sleep, false);
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needwake = true;
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}
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raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
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if (needwake) {
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trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake"));
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wake_up_process(rdp_gp->nocb_gp_kthread);
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}
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return needwake;
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}
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/*
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* Kick the GP kthread for this NOCB group.
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*/
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static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
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{
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unsigned long flags;
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struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
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raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
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return __wake_nocb_gp(rdp_gp, rdp, force, flags);
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}
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/*
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* Arrange to wake the GP kthread for this NOCB group at some future
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* time when it is safe to do so.
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*/
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static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
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const char *reason)
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{
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unsigned long flags;
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struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
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raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
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/*
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* Bypass wakeup overrides previous deferments. In case
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* of callback storm, no need to wake up too early.
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*/
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if (waketype == RCU_NOCB_WAKE_BYPASS) {
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mod_timer(&rdp_gp->nocb_timer, jiffies + 2);
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WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
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} else {
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if (rdp_gp->nocb_defer_wakeup < RCU_NOCB_WAKE)
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mod_timer(&rdp_gp->nocb_timer, jiffies + 1);
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if (rdp_gp->nocb_defer_wakeup < waketype)
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WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
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}
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raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
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trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
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}
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/*
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* Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
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* However, if there is a callback to be enqueued and if ->nocb_bypass
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* proves to be initially empty, just return false because the no-CB GP
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* kthread may need to be awakened in this case.
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*
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* Note that this function always returns true if rhp is NULL.
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*/
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static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
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unsigned long j)
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{
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struct rcu_cblist rcl;
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WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp));
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rcu_lockdep_assert_cblist_protected(rdp);
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lockdep_assert_held(&rdp->nocb_bypass_lock);
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if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) {
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raw_spin_unlock(&rdp->nocb_bypass_lock);
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return false;
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}
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/* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
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if (rhp)
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rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
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rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
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rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
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WRITE_ONCE(rdp->nocb_bypass_first, j);
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rcu_nocb_bypass_unlock(rdp);
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return true;
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}
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/*
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* Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
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* However, if there is a callback to be enqueued and if ->nocb_bypass
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* proves to be initially empty, just return false because the no-CB GP
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* kthread may need to be awakened in this case.
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*
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* Note that this function always returns true if rhp is NULL.
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*/
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static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
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unsigned long j)
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{
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if (!rcu_rdp_is_offloaded(rdp))
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return true;
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rcu_lockdep_assert_cblist_protected(rdp);
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rcu_nocb_bypass_lock(rdp);
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return rcu_nocb_do_flush_bypass(rdp, rhp, j);
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}
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/*
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* If the ->nocb_bypass_lock is immediately available, flush the
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* ->nocb_bypass queue into ->cblist.
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*/
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static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
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{
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rcu_lockdep_assert_cblist_protected(rdp);
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if (!rcu_rdp_is_offloaded(rdp) ||
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!rcu_nocb_bypass_trylock(rdp))
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return;
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WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j));
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}
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/*
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* See whether it is appropriate to use the ->nocb_bypass list in order
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* to control contention on ->nocb_lock. A limited number of direct
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* enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass
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* is non-empty, further callbacks must be placed into ->nocb_bypass,
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* otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch
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* back to direct use of ->cblist. However, ->nocb_bypass should not be
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* used if ->cblist is empty, because otherwise callbacks can be stranded
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* on ->nocb_bypass because we cannot count on the current CPU ever again
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* invoking call_rcu(). The general rule is that if ->nocb_bypass is
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* non-empty, the corresponding no-CBs grace-period kthread must not be
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* in an indefinite sleep state.
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*
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* Finally, it is not permitted to use the bypass during early boot,
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* as doing so would confuse the auto-initialization code. Besides
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* which, there is no point in worrying about lock contention while
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* there is only one CPU in operation.
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*/
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static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
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bool *was_alldone, unsigned long flags)
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{
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unsigned long c;
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unsigned long cur_gp_seq;
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unsigned long j = jiffies;
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long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
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lockdep_assert_irqs_disabled();
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// Pure softirq/rcuc based processing: no bypassing, no
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// locking.
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if (!rcu_rdp_is_offloaded(rdp)) {
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*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
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return false;
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}
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// In the process of (de-)offloading: no bypassing, but
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// locking.
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if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
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rcu_nocb_lock(rdp);
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*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
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return false; /* Not offloaded, no bypassing. */
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}
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// Don't use ->nocb_bypass during early boot.
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if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
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rcu_nocb_lock(rdp);
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WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
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*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
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return false;
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}
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// If we have advanced to a new jiffy, reset counts to allow
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// moving back from ->nocb_bypass to ->cblist.
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if (j == rdp->nocb_nobypass_last) {
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c = rdp->nocb_nobypass_count + 1;
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} else {
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WRITE_ONCE(rdp->nocb_nobypass_last, j);
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c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy;
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if (ULONG_CMP_LT(rdp->nocb_nobypass_count,
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nocb_nobypass_lim_per_jiffy))
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c = 0;
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else if (c > nocb_nobypass_lim_per_jiffy)
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c = nocb_nobypass_lim_per_jiffy;
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}
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WRITE_ONCE(rdp->nocb_nobypass_count, c);
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|
|
// If there hasn't yet been all that many ->cblist enqueues
|
|
// this jiffy, tell the caller to enqueue onto ->cblist. But flush
|
|
// ->nocb_bypass first.
|
|
if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) {
|
|
rcu_nocb_lock(rdp);
|
|
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
|
|
if (*was_alldone)
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("FirstQ"));
|
|
WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j));
|
|
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
|
|
return false; // Caller must enqueue the callback.
|
|
}
|
|
|
|
// If ->nocb_bypass has been used too long or is too full,
|
|
// flush ->nocb_bypass to ->cblist.
|
|
if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) ||
|
|
ncbs >= qhimark) {
|
|
rcu_nocb_lock(rdp);
|
|
if (!rcu_nocb_flush_bypass(rdp, rhp, j)) {
|
|
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
|
|
if (*was_alldone)
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("FirstQ"));
|
|
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
|
|
return false; // Caller must enqueue the callback.
|
|
}
|
|
if (j != rdp->nocb_gp_adv_time &&
|
|
rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
|
|
rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
|
|
rcu_advance_cbs_nowake(rdp->mynode, rdp);
|
|
rdp->nocb_gp_adv_time = j;
|
|
}
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
return true; // Callback already enqueued.
|
|
}
|
|
|
|
// We need to use the bypass.
|
|
rcu_nocb_wait_contended(rdp);
|
|
rcu_nocb_bypass_lock(rdp);
|
|
ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
|
|
rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
|
|
rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
|
|
if (!ncbs) {
|
|
WRITE_ONCE(rdp->nocb_bypass_first, j);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
|
|
}
|
|
rcu_nocb_bypass_unlock(rdp);
|
|
smp_mb(); /* Order enqueue before wake. */
|
|
if (ncbs) {
|
|
local_irq_restore(flags);
|
|
} else {
|
|
// No-CBs GP kthread might be indefinitely asleep, if so, wake.
|
|
rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
|
|
if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("FirstBQwake"));
|
|
__call_rcu_nocb_wake(rdp, true, flags);
|
|
} else {
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("FirstBQnoWake"));
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
}
|
|
}
|
|
return true; // Callback already enqueued.
|
|
}
|
|
|
|
/*
|
|
* Awaken the no-CBs grace-period kthread if needed, either due to it
|
|
* legitimately being asleep or due to overload conditions.
|
|
*
|
|
* If warranted, also wake up the kthread servicing this CPUs queues.
|
|
*/
|
|
static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
|
|
unsigned long flags)
|
|
__releases(rdp->nocb_lock)
|
|
{
|
|
unsigned long cur_gp_seq;
|
|
unsigned long j;
|
|
long len;
|
|
struct task_struct *t;
|
|
|
|
// If we are being polled or there is no kthread, just leave.
|
|
t = READ_ONCE(rdp->nocb_gp_kthread);
|
|
if (rcu_nocb_poll || !t) {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("WakeNotPoll"));
|
|
return;
|
|
}
|
|
// Need to actually to a wakeup.
|
|
len = rcu_segcblist_n_cbs(&rdp->cblist);
|
|
if (was_alldone) {
|
|
rdp->qlen_last_fqs_check = len;
|
|
if (!irqs_disabled_flags(flags)) {
|
|
/* ... if queue was empty ... */
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
wake_nocb_gp(rdp, false);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("WakeEmpty"));
|
|
} else {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
|
|
TPS("WakeEmptyIsDeferred"));
|
|
}
|
|
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
|
|
/* ... or if many callbacks queued. */
|
|
rdp->qlen_last_fqs_check = len;
|
|
j = jiffies;
|
|
if (j != rdp->nocb_gp_adv_time &&
|
|
rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
|
|
rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
|
|
rcu_advance_cbs_nowake(rdp->mynode, rdp);
|
|
rdp->nocb_gp_adv_time = j;
|
|
}
|
|
smp_mb(); /* Enqueue before timer_pending(). */
|
|
if ((rdp->nocb_cb_sleep ||
|
|
!rcu_segcblist_ready_cbs(&rdp->cblist)) &&
|
|
!timer_pending(&rdp->nocb_timer)) {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
|
|
TPS("WakeOvfIsDeferred"));
|
|
} else {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
|
|
}
|
|
} else {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
|
|
}
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Check if we ignore this rdp.
|
|
*
|
|
* We check that without holding the nocb lock but
|
|
* we make sure not to miss a freshly offloaded rdp
|
|
* with the current ordering:
|
|
*
|
|
* rdp_offload_toggle() nocb_gp_enabled_cb()
|
|
* ------------------------- ----------------------------
|
|
* WRITE flags LOCK nocb_gp_lock
|
|
* LOCK nocb_gp_lock READ/WRITE nocb_gp_sleep
|
|
* READ/WRITE nocb_gp_sleep UNLOCK nocb_gp_lock
|
|
* UNLOCK nocb_gp_lock READ flags
|
|
*/
|
|
static inline bool nocb_gp_enabled_cb(struct rcu_data *rdp)
|
|
{
|
|
u8 flags = SEGCBLIST_OFFLOADED | SEGCBLIST_KTHREAD_GP;
|
|
|
|
return rcu_segcblist_test_flags(&rdp->cblist, flags);
|
|
}
|
|
|
|
static inline bool nocb_gp_update_state_deoffloading(struct rcu_data *rdp,
|
|
bool *needwake_state)
|
|
{
|
|
struct rcu_segcblist *cblist = &rdp->cblist;
|
|
|
|
if (rcu_segcblist_test_flags(cblist, SEGCBLIST_OFFLOADED)) {
|
|
if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP)) {
|
|
rcu_segcblist_set_flags(cblist, SEGCBLIST_KTHREAD_GP);
|
|
if (rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB))
|
|
*needwake_state = true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* De-offloading. Clear our flag and notify the de-offload worker.
|
|
* We will ignore this rdp until it ever gets re-offloaded.
|
|
*/
|
|
WARN_ON_ONCE(!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP));
|
|
rcu_segcblist_clear_flags(cblist, SEGCBLIST_KTHREAD_GP);
|
|
if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB))
|
|
*needwake_state = true;
|
|
return true;
|
|
}
|
|
|
|
|
|
/*
|
|
* No-CBs GP kthreads come here to wait for additional callbacks to show up
|
|
* or for grace periods to end.
|
|
*/
|
|
static void nocb_gp_wait(struct rcu_data *my_rdp)
|
|
{
|
|
bool bypass = false;
|
|
long bypass_ncbs;
|
|
int __maybe_unused cpu = my_rdp->cpu;
|
|
unsigned long cur_gp_seq;
|
|
unsigned long flags;
|
|
bool gotcbs = false;
|
|
unsigned long j = jiffies;
|
|
bool needwait_gp = false; // This prevents actual uninitialized use.
|
|
bool needwake;
|
|
bool needwake_gp;
|
|
struct rcu_data *rdp;
|
|
struct rcu_node *rnp;
|
|
unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
|
|
bool wasempty = false;
|
|
|
|
/*
|
|
* Each pass through the following loop checks for CBs and for the
|
|
* nearest grace period (if any) to wait for next. The CB kthreads
|
|
* and the global grace-period kthread are awakened if needed.
|
|
*/
|
|
WARN_ON_ONCE(my_rdp->nocb_gp_rdp != my_rdp);
|
|
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
|
|
bool needwake_state = false;
|
|
|
|
if (!nocb_gp_enabled_cb(rdp))
|
|
continue;
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
|
|
rcu_nocb_lock_irqsave(rdp, flags);
|
|
if (nocb_gp_update_state_deoffloading(rdp, &needwake_state)) {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
if (needwake_state)
|
|
swake_up_one(&rdp->nocb_state_wq);
|
|
continue;
|
|
}
|
|
bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
|
|
if (bypass_ncbs &&
|
|
(time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
|
|
bypass_ncbs > 2 * qhimark)) {
|
|
// Bypass full or old, so flush it.
|
|
(void)rcu_nocb_try_flush_bypass(rdp, j);
|
|
bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
|
|
} else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
if (needwake_state)
|
|
swake_up_one(&rdp->nocb_state_wq);
|
|
continue; /* No callbacks here, try next. */
|
|
}
|
|
if (bypass_ncbs) {
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("Bypass"));
|
|
bypass = true;
|
|
}
|
|
rnp = rdp->mynode;
|
|
|
|
// Advance callbacks if helpful and low contention.
|
|
needwake_gp = false;
|
|
if (!rcu_segcblist_restempty(&rdp->cblist,
|
|
RCU_NEXT_READY_TAIL) ||
|
|
(rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
|
|
rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
|
|
raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
|
|
needwake_gp = rcu_advance_cbs(rnp, rdp);
|
|
wasempty = rcu_segcblist_restempty(&rdp->cblist,
|
|
RCU_NEXT_READY_TAIL);
|
|
raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
|
|
}
|
|
// Need to wait on some grace period?
|
|
WARN_ON_ONCE(wasempty &&
|
|
!rcu_segcblist_restempty(&rdp->cblist,
|
|
RCU_NEXT_READY_TAIL));
|
|
if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
|
|
if (!needwait_gp ||
|
|
ULONG_CMP_LT(cur_gp_seq, wait_gp_seq))
|
|
wait_gp_seq = cur_gp_seq;
|
|
needwait_gp = true;
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("NeedWaitGP"));
|
|
}
|
|
if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
|
|
needwake = rdp->nocb_cb_sleep;
|
|
WRITE_ONCE(rdp->nocb_cb_sleep, false);
|
|
smp_mb(); /* CB invocation -after- GP end. */
|
|
} else {
|
|
needwake = false;
|
|
}
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
if (needwake) {
|
|
swake_up_one(&rdp->nocb_cb_wq);
|
|
gotcbs = true;
|
|
}
|
|
if (needwake_gp)
|
|
rcu_gp_kthread_wake();
|
|
if (needwake_state)
|
|
swake_up_one(&rdp->nocb_state_wq);
|
|
}
|
|
|
|
my_rdp->nocb_gp_bypass = bypass;
|
|
my_rdp->nocb_gp_gp = needwait_gp;
|
|
my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
|
|
|
|
if (bypass && !rcu_nocb_poll) {
|
|
// At least one child with non-empty ->nocb_bypass, so set
|
|
// timer in order to avoid stranding its callbacks.
|
|
wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS,
|
|
TPS("WakeBypassIsDeferred"));
|
|
}
|
|
if (rcu_nocb_poll) {
|
|
/* Polling, so trace if first poll in the series. */
|
|
if (gotcbs)
|
|
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
|
|
schedule_timeout_idle(1);
|
|
} else if (!needwait_gp) {
|
|
/* Wait for callbacks to appear. */
|
|
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
|
|
swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
|
|
!READ_ONCE(my_rdp->nocb_gp_sleep));
|
|
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
|
|
} else {
|
|
rnp = my_rdp->mynode;
|
|
trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));
|
|
swait_event_interruptible_exclusive(
|
|
rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1],
|
|
rcu_seq_done(&rnp->gp_seq, wait_gp_seq) ||
|
|
!READ_ONCE(my_rdp->nocb_gp_sleep));
|
|
trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait"));
|
|
}
|
|
if (!rcu_nocb_poll) {
|
|
raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
|
|
if (my_rdp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
|
|
WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
|
|
del_timer(&my_rdp->nocb_timer);
|
|
}
|
|
WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
|
|
raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
|
|
}
|
|
my_rdp->nocb_gp_seq = -1;
|
|
WARN_ON(signal_pending(current));
|
|
}
|
|
|
|
/*
|
|
* No-CBs grace-period-wait kthread. There is one of these per group
|
|
* of CPUs, but only once at least one CPU in that group has come online
|
|
* at least once since boot. This kthread checks for newly posted
|
|
* callbacks from any of the CPUs it is responsible for, waits for a
|
|
* grace period, then awakens all of the rcu_nocb_cb_kthread() instances
|
|
* that then have callback-invocation work to do.
|
|
*/
|
|
static int rcu_nocb_gp_kthread(void *arg)
|
|
{
|
|
struct rcu_data *rdp = arg;
|
|
|
|
for (;;) {
|
|
WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
|
|
nocb_gp_wait(rdp);
|
|
cond_resched_tasks_rcu_qs();
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
static inline bool nocb_cb_can_run(struct rcu_data *rdp)
|
|
{
|
|
u8 flags = SEGCBLIST_OFFLOADED | SEGCBLIST_KTHREAD_CB;
|
|
return rcu_segcblist_test_flags(&rdp->cblist, flags);
|
|
}
|
|
|
|
static inline bool nocb_cb_wait_cond(struct rcu_data *rdp)
|
|
{
|
|
return nocb_cb_can_run(rdp) && !READ_ONCE(rdp->nocb_cb_sleep);
|
|
}
|
|
|
|
/*
|
|
* Invoke any ready callbacks from the corresponding no-CBs CPU,
|
|
* then, if there are no more, wait for more to appear.
|
|
*/
|
|
static void nocb_cb_wait(struct rcu_data *rdp)
|
|
{
|
|
struct rcu_segcblist *cblist = &rdp->cblist;
|
|
unsigned long cur_gp_seq;
|
|
unsigned long flags;
|
|
bool needwake_state = false;
|
|
bool needwake_gp = false;
|
|
bool can_sleep = true;
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
local_irq_save(flags);
|
|
rcu_momentary_dyntick_idle();
|
|
local_irq_restore(flags);
|
|
/*
|
|
* Disable BH to provide the expected environment. Also, when
|
|
* transitioning to/from NOCB mode, a self-requeuing callback might
|
|
* be invoked from softirq. A short grace period could cause both
|
|
* instances of this callback would execute concurrently.
|
|
*/
|
|
local_bh_disable();
|
|
rcu_do_batch(rdp);
|
|
local_bh_enable();
|
|
lockdep_assert_irqs_enabled();
|
|
rcu_nocb_lock_irqsave(rdp, flags);
|
|
if (rcu_segcblist_nextgp(cblist, &cur_gp_seq) &&
|
|
rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
|
|
raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
|
|
needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
|
|
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
|
|
}
|
|
|
|
if (rcu_segcblist_test_flags(cblist, SEGCBLIST_OFFLOADED)) {
|
|
if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB)) {
|
|
rcu_segcblist_set_flags(cblist, SEGCBLIST_KTHREAD_CB);
|
|
if (rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP))
|
|
needwake_state = true;
|
|
}
|
|
if (rcu_segcblist_ready_cbs(cblist))
|
|
can_sleep = false;
|
|
} else {
|
|
/*
|
|
* De-offloading. Clear our flag and notify the de-offload worker.
|
|
* We won't touch the callbacks and keep sleeping until we ever
|
|
* get re-offloaded.
|
|
*/
|
|
WARN_ON_ONCE(!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB));
|
|
rcu_segcblist_clear_flags(cblist, SEGCBLIST_KTHREAD_CB);
|
|
if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP))
|
|
needwake_state = true;
|
|
}
|
|
|
|
WRITE_ONCE(rdp->nocb_cb_sleep, can_sleep);
|
|
|
|
if (rdp->nocb_cb_sleep)
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
|
|
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
if (needwake_gp)
|
|
rcu_gp_kthread_wake();
|
|
|
|
if (needwake_state)
|
|
swake_up_one(&rdp->nocb_state_wq);
|
|
|
|
do {
|
|
swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
|
|
nocb_cb_wait_cond(rdp));
|
|
|
|
// VVV Ensure CB invocation follows _sleep test.
|
|
if (smp_load_acquire(&rdp->nocb_cb_sleep)) { // ^^^
|
|
WARN_ON(signal_pending(current));
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
|
|
}
|
|
} while (!nocb_cb_can_run(rdp));
|
|
}
|
|
|
|
/*
|
|
* Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
|
|
* nocb_cb_wait() to do the dirty work.
|
|
*/
|
|
static int rcu_nocb_cb_kthread(void *arg)
|
|
{
|
|
struct rcu_data *rdp = arg;
|
|
|
|
// Each pass through this loop does one callback batch, and,
|
|
// if there are no more ready callbacks, waits for them.
|
|
for (;;) {
|
|
nocb_cb_wait(rdp);
|
|
cond_resched_tasks_rcu_qs();
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
|
|
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
|
|
{
|
|
return READ_ONCE(rdp->nocb_defer_wakeup) >= level;
|
|
}
|
|
|
|
/* Do a deferred wakeup of rcu_nocb_kthread(). */
|
|
static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp_gp,
|
|
struct rcu_data *rdp, int level,
|
|
unsigned long flags)
|
|
__releases(rdp_gp->nocb_gp_lock)
|
|
{
|
|
int ndw;
|
|
int ret;
|
|
|
|
if (!rcu_nocb_need_deferred_wakeup(rdp_gp, level)) {
|
|
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
|
|
return false;
|
|
}
|
|
|
|
ndw = rdp_gp->nocb_defer_wakeup;
|
|
ret = __wake_nocb_gp(rdp_gp, rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake"));
|
|
|
|
return ret;
|
|
}
|
|
|
|
/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
|
|
static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
|
|
|
|
WARN_ON_ONCE(rdp->nocb_gp_rdp != rdp);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer"));
|
|
|
|
raw_spin_lock_irqsave(&rdp->nocb_gp_lock, flags);
|
|
smp_mb__after_spinlock(); /* Timer expire before wakeup. */
|
|
do_nocb_deferred_wakeup_common(rdp, rdp, RCU_NOCB_WAKE_BYPASS, flags);
|
|
}
|
|
|
|
/*
|
|
* Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
|
|
* This means we do an inexact common-case check. Note that if
|
|
* we miss, ->nocb_timer will eventually clean things up.
|
|
*/
|
|
static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
|
|
|
|
if (!rdp_gp || !rcu_nocb_need_deferred_wakeup(rdp_gp, RCU_NOCB_WAKE))
|
|
return false;
|
|
|
|
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
|
|
return do_nocb_deferred_wakeup_common(rdp_gp, rdp, RCU_NOCB_WAKE, flags);
|
|
}
|
|
|
|
void rcu_nocb_flush_deferred_wakeup(void)
|
|
{
|
|
do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data));
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_nocb_flush_deferred_wakeup);
|
|
|
|
static int rdp_offload_toggle(struct rcu_data *rdp,
|
|
bool offload, unsigned long flags)
|
|
__releases(rdp->nocb_lock)
|
|
{
|
|
struct rcu_segcblist *cblist = &rdp->cblist;
|
|
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
|
|
bool wake_gp = false;
|
|
|
|
rcu_segcblist_offload(cblist, offload);
|
|
|
|
if (rdp->nocb_cb_sleep)
|
|
rdp->nocb_cb_sleep = false;
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
|
|
/*
|
|
* Ignore former value of nocb_cb_sleep and force wake up as it could
|
|
* have been spuriously set to false already.
|
|
*/
|
|
swake_up_one(&rdp->nocb_cb_wq);
|
|
|
|
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
|
|
if (rdp_gp->nocb_gp_sleep) {
|
|
rdp_gp->nocb_gp_sleep = false;
|
|
wake_gp = true;
|
|
}
|
|
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
|
|
|
|
if (wake_gp)
|
|
wake_up_process(rdp_gp->nocb_gp_kthread);
|
|
|
|
return 0;
|
|
}
|
|
|
|
static long rcu_nocb_rdp_deoffload(void *arg)
|
|
{
|
|
struct rcu_data *rdp = arg;
|
|
struct rcu_segcblist *cblist = &rdp->cblist;
|
|
unsigned long flags;
|
|
int ret;
|
|
|
|
WARN_ON_ONCE(rdp->cpu != raw_smp_processor_id());
|
|
|
|
pr_info("De-offloading %d\n", rdp->cpu);
|
|
|
|
rcu_nocb_lock_irqsave(rdp, flags);
|
|
/*
|
|
* Flush once and for all now. This suffices because we are
|
|
* running on the target CPU holding ->nocb_lock (thus having
|
|
* interrupts disabled), and because rdp_offload_toggle()
|
|
* invokes rcu_segcblist_offload(), which clears SEGCBLIST_OFFLOADED.
|
|
* Thus future calls to rcu_segcblist_completely_offloaded() will
|
|
* return false, which means that future calls to rcu_nocb_try_bypass()
|
|
* will refuse to put anything into the bypass.
|
|
*/
|
|
WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
|
|
ret = rdp_offload_toggle(rdp, false, flags);
|
|
swait_event_exclusive(rdp->nocb_state_wq,
|
|
!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB |
|
|
SEGCBLIST_KTHREAD_GP));
|
|
/*
|
|
* Lock one last time to acquire latest callback updates from kthreads
|
|
* so we can later handle callbacks locally without locking.
|
|
*/
|
|
rcu_nocb_lock_irqsave(rdp, flags);
|
|
/*
|
|
* Theoretically we could set SEGCBLIST_SOFTIRQ_ONLY after the nocb
|
|
* lock is released but how about being paranoid for once?
|
|
*/
|
|
rcu_segcblist_set_flags(cblist, SEGCBLIST_SOFTIRQ_ONLY);
|
|
/*
|
|
* With SEGCBLIST_SOFTIRQ_ONLY, we can't use
|
|
* rcu_nocb_unlock_irqrestore() anymore.
|
|
*/
|
|
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
|
|
|
|
/* Sanity check */
|
|
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
|
|
|
|
|
|
return ret;
|
|
}
|
|
|
|
int rcu_nocb_cpu_deoffload(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
int ret = 0;
|
|
|
|
mutex_lock(&rcu_state.barrier_mutex);
|
|
cpus_read_lock();
|
|
if (rcu_rdp_is_offloaded(rdp)) {
|
|
if (cpu_online(cpu)) {
|
|
ret = work_on_cpu(cpu, rcu_nocb_rdp_deoffload, rdp);
|
|
if (!ret)
|
|
cpumask_clear_cpu(cpu, rcu_nocb_mask);
|
|
} else {
|
|
pr_info("NOCB: Can't CB-deoffload an offline CPU\n");
|
|
ret = -EINVAL;
|
|
}
|
|
}
|
|
cpus_read_unlock();
|
|
mutex_unlock(&rcu_state.barrier_mutex);
|
|
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_nocb_cpu_deoffload);
|
|
|
|
static long rcu_nocb_rdp_offload(void *arg)
|
|
{
|
|
struct rcu_data *rdp = arg;
|
|
struct rcu_segcblist *cblist = &rdp->cblist;
|
|
unsigned long flags;
|
|
int ret;
|
|
|
|
WARN_ON_ONCE(rdp->cpu != raw_smp_processor_id());
|
|
/*
|
|
* For now we only support re-offload, ie: the rdp must have been
|
|
* offloaded on boot first.
|
|
*/
|
|
if (!rdp->nocb_gp_rdp)
|
|
return -EINVAL;
|
|
|
|
pr_info("Offloading %d\n", rdp->cpu);
|
|
/*
|
|
* Can't use rcu_nocb_lock_irqsave() while we are in
|
|
* SEGCBLIST_SOFTIRQ_ONLY mode.
|
|
*/
|
|
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
|
|
|
|
/*
|
|
* We didn't take the nocb lock while working on the
|
|
* rdp->cblist in SEGCBLIST_SOFTIRQ_ONLY mode.
|
|
* Every modifications that have been done previously on
|
|
* rdp->cblist must be visible remotely by the nocb kthreads
|
|
* upon wake up after reading the cblist flags.
|
|
*
|
|
* The layout against nocb_lock enforces that ordering:
|
|
*
|
|
* __rcu_nocb_rdp_offload() nocb_cb_wait()/nocb_gp_wait()
|
|
* ------------------------- ----------------------------
|
|
* WRITE callbacks rcu_nocb_lock()
|
|
* rcu_nocb_lock() READ flags
|
|
* WRITE flags READ callbacks
|
|
* rcu_nocb_unlock() rcu_nocb_unlock()
|
|
*/
|
|
ret = rdp_offload_toggle(rdp, true, flags);
|
|
swait_event_exclusive(rdp->nocb_state_wq,
|
|
rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&
|
|
rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP));
|
|
|
|
return ret;
|
|
}
|
|
|
|
int rcu_nocb_cpu_offload(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
int ret = 0;
|
|
|
|
mutex_lock(&rcu_state.barrier_mutex);
|
|
cpus_read_lock();
|
|
if (!rcu_rdp_is_offloaded(rdp)) {
|
|
if (cpu_online(cpu)) {
|
|
ret = work_on_cpu(cpu, rcu_nocb_rdp_offload, rdp);
|
|
if (!ret)
|
|
cpumask_set_cpu(cpu, rcu_nocb_mask);
|
|
} else {
|
|
pr_info("NOCB: Can't CB-offload an offline CPU\n");
|
|
ret = -EINVAL;
|
|
}
|
|
}
|
|
cpus_read_unlock();
|
|
mutex_unlock(&rcu_state.barrier_mutex);
|
|
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
|
|
|
|
void __init rcu_init_nohz(void)
|
|
{
|
|
int cpu;
|
|
bool need_rcu_nocb_mask = false;
|
|
struct rcu_data *rdp;
|
|
|
|
#if defined(CONFIG_NO_HZ_FULL)
|
|
if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
|
|
need_rcu_nocb_mask = true;
|
|
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
|
|
|
|
if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
|
|
if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
|
|
pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
|
|
return;
|
|
}
|
|
}
|
|
if (!cpumask_available(rcu_nocb_mask))
|
|
return;
|
|
|
|
#if defined(CONFIG_NO_HZ_FULL)
|
|
if (tick_nohz_full_running)
|
|
cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
|
|
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
|
|
|
|
if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
|
|
pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
|
|
cpumask_and(rcu_nocb_mask, cpu_possible_mask,
|
|
rcu_nocb_mask);
|
|
}
|
|
if (cpumask_empty(rcu_nocb_mask))
|
|
pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
|
|
else
|
|
pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
|
|
cpumask_pr_args(rcu_nocb_mask));
|
|
if (rcu_nocb_poll)
|
|
pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
|
|
|
|
for_each_cpu(cpu, rcu_nocb_mask) {
|
|
rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
if (rcu_segcblist_empty(&rdp->cblist))
|
|
rcu_segcblist_init(&rdp->cblist);
|
|
rcu_segcblist_offload(&rdp->cblist, true);
|
|
rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_CB);
|
|
rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_GP);
|
|
}
|
|
rcu_organize_nocb_kthreads();
|
|
}
|
|
|
|
/* Initialize per-rcu_data variables for no-CBs CPUs. */
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
|
|
init_swait_queue_head(&rdp->nocb_cb_wq);
|
|
init_swait_queue_head(&rdp->nocb_gp_wq);
|
|
init_swait_queue_head(&rdp->nocb_state_wq);
|
|
raw_spin_lock_init(&rdp->nocb_lock);
|
|
raw_spin_lock_init(&rdp->nocb_bypass_lock);
|
|
raw_spin_lock_init(&rdp->nocb_gp_lock);
|
|
timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
|
|
rcu_cblist_init(&rdp->nocb_bypass);
|
|
}
|
|
|
|
/*
|
|
* If the specified CPU is a no-CBs CPU that does not already have its
|
|
* rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
|
|
* for this CPU's group has not yet been created, spawn it as well.
|
|
*/
|
|
static void rcu_spawn_one_nocb_kthread(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
struct rcu_data *rdp_gp;
|
|
struct task_struct *t;
|
|
|
|
/*
|
|
* If this isn't a no-CBs CPU or if it already has an rcuo kthread,
|
|
* then nothing to do.
|
|
*/
|
|
if (!rcu_is_nocb_cpu(cpu) || rdp->nocb_cb_kthread)
|
|
return;
|
|
|
|
/* If we didn't spawn the GP kthread first, reorganize! */
|
|
rdp_gp = rdp->nocb_gp_rdp;
|
|
if (!rdp_gp->nocb_gp_kthread) {
|
|
t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
|
|
"rcuog/%d", rdp_gp->cpu);
|
|
if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__))
|
|
return;
|
|
WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
|
|
}
|
|
|
|
/* Spawn the kthread for this CPU. */
|
|
t = kthread_run(rcu_nocb_cb_kthread, rdp,
|
|
"rcuo%c/%d", rcu_state.abbr, cpu);
|
|
if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
|
|
return;
|
|
WRITE_ONCE(rdp->nocb_cb_kthread, t);
|
|
WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
|
|
}
|
|
|
|
/*
|
|
* If the specified CPU is a no-CBs CPU that does not already have its
|
|
* rcuo kthread, spawn it.
|
|
*/
|
|
static void rcu_spawn_cpu_nocb_kthread(int cpu)
|
|
{
|
|
if (rcu_scheduler_fully_active)
|
|
rcu_spawn_one_nocb_kthread(cpu);
|
|
}
|
|
|
|
/*
|
|
* Once the scheduler is running, spawn rcuo kthreads for all online
|
|
* no-CBs CPUs. This assumes that the early_initcall()s happen before
|
|
* non-boot CPUs come online -- if this changes, we will need to add
|
|
* some mutual exclusion.
|
|
*/
|
|
static void __init rcu_spawn_nocb_kthreads(void)
|
|
{
|
|
int cpu;
|
|
|
|
for_each_online_cpu(cpu)
|
|
rcu_spawn_cpu_nocb_kthread(cpu);
|
|
}
|
|
|
|
/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
|
|
static int rcu_nocb_gp_stride = -1;
|
|
module_param(rcu_nocb_gp_stride, int, 0444);
|
|
|
|
/*
|
|
* Initialize GP-CB relationships for all no-CBs CPU.
|
|
*/
|
|
static void __init rcu_organize_nocb_kthreads(void)
|
|
{
|
|
int cpu;
|
|
bool firsttime = true;
|
|
bool gotnocbs = false;
|
|
bool gotnocbscbs = true;
|
|
int ls = rcu_nocb_gp_stride;
|
|
int nl = 0; /* Next GP kthread. */
|
|
struct rcu_data *rdp;
|
|
struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */
|
|
struct rcu_data *rdp_prev = NULL;
|
|
|
|
if (!cpumask_available(rcu_nocb_mask))
|
|
return;
|
|
if (ls == -1) {
|
|
ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
|
|
rcu_nocb_gp_stride = ls;
|
|
}
|
|
|
|
/*
|
|
* Each pass through this loop sets up one rcu_data structure.
|
|
* Should the corresponding CPU come online in the future, then
|
|
* we will spawn the needed set of rcu_nocb_kthread() kthreads.
|
|
*/
|
|
for_each_cpu(cpu, rcu_nocb_mask) {
|
|
rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
if (rdp->cpu >= nl) {
|
|
/* New GP kthread, set up for CBs & next GP. */
|
|
gotnocbs = true;
|
|
nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
|
|
rdp->nocb_gp_rdp = rdp;
|
|
rdp_gp = rdp;
|
|
if (dump_tree) {
|
|
if (!firsttime)
|
|
pr_cont("%s\n", gotnocbscbs
|
|
? "" : " (self only)");
|
|
gotnocbscbs = false;
|
|
firsttime = false;
|
|
pr_alert("%s: No-CB GP kthread CPU %d:",
|
|
__func__, cpu);
|
|
}
|
|
} else {
|
|
/* Another CB kthread, link to previous GP kthread. */
|
|
gotnocbscbs = true;
|
|
rdp->nocb_gp_rdp = rdp_gp;
|
|
rdp_prev->nocb_next_cb_rdp = rdp;
|
|
if (dump_tree)
|
|
pr_cont(" %d", cpu);
|
|
}
|
|
rdp_prev = rdp;
|
|
}
|
|
if (gotnocbs && dump_tree)
|
|
pr_cont("%s\n", gotnocbscbs ? "" : " (self only)");
|
|
}
|
|
|
|
/*
|
|
* Bind the current task to the offloaded CPUs. If there are no offloaded
|
|
* CPUs, leave the task unbound. Splat if the bind attempt fails.
|
|
*/
|
|
void rcu_bind_current_to_nocb(void)
|
|
{
|
|
if (cpumask_available(rcu_nocb_mask) && cpumask_weight(rcu_nocb_mask))
|
|
WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
|
|
|
|
// The ->on_cpu field is available only in CONFIG_SMP=y, so...
|
|
#ifdef CONFIG_SMP
|
|
static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
|
|
{
|
|
return tsp && task_is_running(tsp) && !tsp->on_cpu ? "!" : "";
|
|
}
|
|
#else // #ifdef CONFIG_SMP
|
|
static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
|
|
{
|
|
return "";
|
|
}
|
|
#endif // #else #ifdef CONFIG_SMP
|
|
|
|
/*
|
|
* Dump out nocb grace-period kthread state for the specified rcu_data
|
|
* structure.
|
|
*/
|
|
static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
|
|
{
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
pr_info("nocb GP %d %c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu %c CPU %d%s\n",
|
|
rdp->cpu,
|
|
"kK"[!!rdp->nocb_gp_kthread],
|
|
"lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
|
|
"dD"[!!rdp->nocb_defer_wakeup],
|
|
"tT"[timer_pending(&rdp->nocb_timer)],
|
|
"sS"[!!rdp->nocb_gp_sleep],
|
|
".W"[swait_active(&rdp->nocb_gp_wq)],
|
|
".W"[swait_active(&rnp->nocb_gp_wq[0])],
|
|
".W"[swait_active(&rnp->nocb_gp_wq[1])],
|
|
".B"[!!rdp->nocb_gp_bypass],
|
|
".G"[!!rdp->nocb_gp_gp],
|
|
(long)rdp->nocb_gp_seq,
|
|
rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops),
|
|
rdp->nocb_gp_kthread ? task_state_to_char(rdp->nocb_gp_kthread) : '.',
|
|
rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
|
|
show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread));
|
|
}
|
|
|
|
/* Dump out nocb kthread state for the specified rcu_data structure. */
|
|
static void show_rcu_nocb_state(struct rcu_data *rdp)
|
|
{
|
|
char bufw[20];
|
|
char bufr[20];
|
|
struct rcu_segcblist *rsclp = &rdp->cblist;
|
|
bool waslocked;
|
|
bool wassleep;
|
|
|
|
if (rdp->nocb_gp_rdp == rdp)
|
|
show_rcu_nocb_gp_state(rdp);
|
|
|
|
sprintf(bufw, "%ld", rsclp->gp_seq[RCU_WAIT_TAIL]);
|
|
sprintf(bufr, "%ld", rsclp->gp_seq[RCU_NEXT_READY_TAIL]);
|
|
pr_info(" CB %d^%d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%s%c%s%c%c q%ld %c CPU %d%s\n",
|
|
rdp->cpu, rdp->nocb_gp_rdp->cpu,
|
|
rdp->nocb_next_cb_rdp ? rdp->nocb_next_cb_rdp->cpu : -1,
|
|
"kK"[!!rdp->nocb_cb_kthread],
|
|
"bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
|
|
"cC"[!!atomic_read(&rdp->nocb_lock_contended)],
|
|
"lL"[raw_spin_is_locked(&rdp->nocb_lock)],
|
|
"sS"[!!rdp->nocb_cb_sleep],
|
|
".W"[swait_active(&rdp->nocb_cb_wq)],
|
|
jiffies - rdp->nocb_bypass_first,
|
|
jiffies - rdp->nocb_nobypass_last,
|
|
rdp->nocb_nobypass_count,
|
|
".D"[rcu_segcblist_ready_cbs(rsclp)],
|
|
".W"[!rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL)],
|
|
rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL) ? "" : bufw,
|
|
".R"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL)],
|
|
rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL) ? "" : bufr,
|
|
".N"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_TAIL)],
|
|
".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
|
|
rcu_segcblist_n_cbs(&rdp->cblist),
|
|
rdp->nocb_cb_kthread ? task_state_to_char(rdp->nocb_cb_kthread) : '.',
|
|
rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
|
|
show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread));
|
|
|
|
/* It is OK for GP kthreads to have GP state. */
|
|
if (rdp->nocb_gp_rdp == rdp)
|
|
return;
|
|
|
|
waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
|
|
wassleep = swait_active(&rdp->nocb_gp_wq);
|
|
if (!rdp->nocb_gp_sleep && !waslocked && !wassleep)
|
|
return; /* Nothing untoward. */
|
|
|
|
pr_info(" nocb GP activity on CB-only CPU!!! %c%c%c %c\n",
|
|
"lL"[waslocked],
|
|
"dD"[!!rdp->nocb_defer_wakeup],
|
|
"sS"[!!rdp->nocb_gp_sleep],
|
|
".W"[wassleep]);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
|
|
|
|
static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
/* No ->nocb_lock to acquire. */
|
|
static void rcu_nocb_lock(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
/* No ->nocb_lock to release. */
|
|
static void rcu_nocb_unlock(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
/* No ->nocb_lock to release. */
|
|
static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
|
|
unsigned long flags)
|
|
{
|
|
local_irq_restore(flags);
|
|
}
|
|
|
|
/* Lockdep check that ->cblist may be safely accessed. */
|
|
static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
|
|
{
|
|
lockdep_assert_irqs_disabled();
|
|
}
|
|
|
|
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
|
|
{
|
|
}
|
|
|
|
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
|
|
{
|
|
return NULL;
|
|
}
|
|
|
|
static void rcu_init_one_nocb(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
unsigned long j)
|
|
{
|
|
return true;
|
|
}
|
|
|
|
static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
bool *was_alldone, unsigned long flags)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
|
|
unsigned long flags)
|
|
{
|
|
WARN_ON_ONCE(1); /* Should be dead code! */
|
|
}
|
|
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void rcu_spawn_cpu_nocb_kthread(int cpu)
|
|
{
|
|
}
|
|
|
|
static void __init rcu_spawn_nocb_kthreads(void)
|
|
{
|
|
}
|
|
|
|
static void show_rcu_nocb_state(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
|