rcu: Simplify offline processing
Move ->qsmaskinit and blkd_tasks[] manipulation to the CPU_DYING notifier. This simplifies the code by eliminating a potential deadlock and by reducing the responsibilities of force_quiescent_state(). Also rename functions to make their connection to the CPU-hotplug stages explicit. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
Paul E. McKenney
parent
ae1f18e480
commit
e560140008
3 changed files with 88 additions and 97 deletions
156
kernel/rcutree.c
156
kernel/rcutree.c
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@ -943,6 +943,10 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat
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* in preparation for detecting the next grace period. The caller must hold
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* the root node's ->lock, which is released before return. Hard irqs must
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* be disabled.
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*
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* Note that it is legal for a dying CPU (which is marked as offline) to
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* invoke this function. This can happen when the dying CPU reports its
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* quiescent state.
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*/
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static void
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rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
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@ -1245,118 +1249,101 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
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/*
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* Move a dying CPU's RCU callbacks to online CPU's callback list.
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* Synchronization is not required because this function executes
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* in stop_machine() context.
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* Also record a quiescent state for this CPU for the current grace period.
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* Synchronization and interrupt disabling are not required because
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* this function executes in stop_machine() context. Therefore, cleanup
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* operations that might block must be done later from the CPU_DEAD
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* notifier.
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*
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* Note that the outgoing CPU's bit has already been cleared in the
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* cpu_online_mask. This allows us to randomly pick a callback
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* destination from the bits set in that mask.
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*/
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static void rcu_send_cbs_to_online(struct rcu_state *rsp)
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static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
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{
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unsigned long flags;
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int i;
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/* current DYING CPU is cleared in the cpu_online_mask */
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unsigned long mask;
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int need_report;
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int receive_cpu = cpumask_any(cpu_online_mask);
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struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
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struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu);
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struct rcu_node *rnp = rdp->mynode; /* For dying CPU. */
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if (rdp->nxtlist == NULL)
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return; /* irqs disabled, so comparison is stable. */
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/* Move callbacks to some other CPU. */
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if (rdp->nxtlist != NULL) {
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*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
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receive_rdp->nxttail[RCU_NEXT_TAIL] =
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rdp->nxttail[RCU_NEXT_TAIL];
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receive_rdp->qlen_lazy += rdp->qlen_lazy;
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receive_rdp->qlen += rdp->qlen;
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receive_rdp->n_cbs_adopted += rdp->qlen;
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rdp->n_cbs_orphaned += rdp->qlen;
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*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
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receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
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receive_rdp->qlen_lazy += rdp->qlen_lazy;
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receive_rdp->qlen += rdp->qlen;
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receive_rdp->n_cbs_adopted += rdp->qlen;
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rdp->n_cbs_orphaned += rdp->qlen;
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rdp->nxtlist = NULL;
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for (i = 0; i < RCU_NEXT_SIZE; i++)
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rdp->nxttail[i] = &rdp->nxtlist;
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rdp->qlen_lazy = 0;
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rdp->qlen = 0;
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}
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rdp->nxtlist = NULL;
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for (i = 0; i < RCU_NEXT_SIZE; i++)
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rdp->nxttail[i] = &rdp->nxtlist;
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rdp->qlen_lazy = 0;
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rdp->qlen = 0;
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}
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/*
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* Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
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* and move all callbacks from the outgoing CPU to the current one.
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* There can only be one CPU hotplug operation at a time, so no other
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* CPU can be attempting to update rcu_cpu_kthread_task.
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*/
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static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
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{
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unsigned long flags;
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unsigned long mask;
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int need_report = 0;
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struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
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struct rcu_node *rnp;
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rcu_stop_cpu_kthread(cpu);
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/* Exclude any attempts to start a new grace period. */
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raw_spin_lock_irqsave(&rsp->onofflock, flags);
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/* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
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rnp = rdp->mynode; /* this is the outgoing CPU's rnp. */
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/* Record a quiescent state for the dying CPU. */
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mask = rdp->grpmask; /* rnp->grplo is constant. */
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trace_rcu_grace_period(rsp->name,
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rnp->gpnum + 1 - !!(rnp->qsmask & mask),
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"cpuofl");
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rcu_report_qs_rdp(smp_processor_id(), rsp, rdp, rsp->gpnum);
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/* Note that rcu_report_qs_rdp() might call trace_rcu_grace_period(). */
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/*
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* Remove the dying CPU from the bitmasks in the rcu_node
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* hierarchy. Because we are in stop_machine() context, we
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* automatically exclude ->onofflock critical sections.
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*/
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do {
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raw_spin_lock(&rnp->lock); /* irqs already disabled. */
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raw_spin_lock_irqsave(&rnp->lock, flags);
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rnp->qsmaskinit &= ~mask;
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if (rnp->qsmaskinit != 0) {
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if (rnp != rdp->mynode)
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
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else
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trace_rcu_grace_period(rsp->name,
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rnp->gpnum + 1 -
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!!(rnp->qsmask & mask),
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"cpuofl");
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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break;
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}
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if (rnp == rdp->mynode) {
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trace_rcu_grace_period(rsp->name,
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rnp->gpnum + 1 -
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!!(rnp->qsmask & mask),
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"cpuofl");
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need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
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if (need_report & RCU_OFL_TASKS_NORM_GP)
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rcu_report_unblock_qs_rnp(rnp, flags);
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else
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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if (need_report & RCU_OFL_TASKS_EXP_GP)
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rcu_report_exp_rnp(rsp, rnp, true);
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} else
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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mask = rnp->grpmask;
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rnp = rnp->parent;
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} while (rnp != NULL);
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/*
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* We still hold the leaf rcu_node structure lock here, and
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* irqs are still disabled. The reason for this subterfuge is
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* because invoking rcu_report_unblock_qs_rnp() with ->onofflock
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* held leads to deadlock.
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*/
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raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
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rnp = rdp->mynode;
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if (need_report & RCU_OFL_TASKS_NORM_GP)
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rcu_report_unblock_qs_rnp(rnp, flags);
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else
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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if (need_report & RCU_OFL_TASKS_EXP_GP)
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rcu_report_exp_rnp(rsp, rnp, true);
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rcu_node_kthread_setaffinity(rnp, -1);
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}
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/*
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* Remove the specified CPU from the RCU hierarchy and move any pending
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* callbacks that it might have to the current CPU. This code assumes
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* that at least one CPU in the system will remain running at all times.
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* Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
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* The CPU has been completely removed, and some other CPU is reporting
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* this fact from process context. Do the remainder of the cleanup.
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* There can only be one CPU hotplug operation at a time, so no other
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* CPU can be attempting to update rcu_cpu_kthread_task.
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*/
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static void rcu_offline_cpu(int cpu)
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static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
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{
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__rcu_offline_cpu(cpu, &rcu_sched_state);
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__rcu_offline_cpu(cpu, &rcu_bh_state);
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rcu_preempt_offline_cpu(cpu);
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struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
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struct rcu_node *rnp = rdp->mynode;
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rcu_stop_cpu_kthread(cpu);
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rcu_node_kthread_setaffinity(rnp, -1);
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}
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#else /* #ifdef CONFIG_HOTPLUG_CPU */
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static void rcu_send_cbs_to_online(struct rcu_state *rsp)
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static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
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{
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}
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static void rcu_offline_cpu(int cpu)
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static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
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{
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}
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@ -1725,6 +1712,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
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* a quiescent state betweentimes.
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*/
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local_irq_save(flags);
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WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
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rdp = this_cpu_ptr(rsp->rda);
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/* Add the callback to our list. */
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@ -2155,16 +2143,18 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
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* touch any data without introducing corruption. We send the
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* dying CPU's callbacks to an arbitrarily chosen online CPU.
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*/
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rcu_send_cbs_to_online(&rcu_bh_state);
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rcu_send_cbs_to_online(&rcu_sched_state);
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rcu_preempt_send_cbs_to_online();
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rcu_cleanup_dying_cpu(&rcu_bh_state);
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rcu_cleanup_dying_cpu(&rcu_sched_state);
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rcu_preempt_cleanup_dying_cpu();
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rcu_cleanup_after_idle(cpu);
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break;
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case CPU_DEAD:
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case CPU_DEAD_FROZEN:
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case CPU_UP_CANCELED:
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case CPU_UP_CANCELED_FROZEN:
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rcu_offline_cpu(cpu);
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rcu_cleanup_dead_cpu(cpu, &rcu_bh_state);
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rcu_cleanup_dead_cpu(cpu, &rcu_sched_state);
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rcu_preempt_cleanup_dead_cpu(cpu);
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break;
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default:
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break;
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@ -439,8 +439,8 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
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static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
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struct rcu_node *rnp,
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struct rcu_data *rdp);
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static void rcu_preempt_offline_cpu(int cpu);
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#endif /* #ifdef CONFIG_HOTPLUG_CPU */
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static void rcu_preempt_cleanup_dead_cpu(int cpu);
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static void rcu_preempt_check_callbacks(int cpu);
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static void rcu_preempt_process_callbacks(void);
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void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
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@ -451,7 +451,7 @@ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
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static int rcu_preempt_pending(int cpu);
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static int rcu_preempt_needs_cpu(int cpu);
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static void __cpuinit rcu_preempt_init_percpu_data(int cpu);
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static void rcu_preempt_send_cbs_to_online(void);
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static void rcu_preempt_cleanup_dying_cpu(void);
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static void __init __rcu_init_preempt(void);
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static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
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static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
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@ -618,16 +618,16 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
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return retval;
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}
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#endif /* #ifdef CONFIG_HOTPLUG_CPU */
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/*
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* Do CPU-offline processing for preemptible RCU.
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*/
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static void rcu_preempt_offline_cpu(int cpu)
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static void rcu_preempt_cleanup_dead_cpu(int cpu)
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{
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__rcu_offline_cpu(cpu, &rcu_preempt_state);
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rcu_cleanup_dead_cpu(cpu, &rcu_preempt_state);
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}
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#endif /* #ifdef CONFIG_HOTPLUG_CPU */
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/*
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* Check for a quiescent state from the current CPU. When a task blocks,
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* the task is recorded in the corresponding CPU's rcu_node structure,
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@ -912,11 +912,12 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
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}
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/*
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* Move preemptible RCU's callbacks from dying CPU to other online CPU.
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* Move preemptible RCU's callbacks from dying CPU to other online CPU
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* and record a quiescent state.
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*/
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static void rcu_preempt_send_cbs_to_online(void)
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static void rcu_preempt_cleanup_dying_cpu(void)
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{
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rcu_send_cbs_to_online(&rcu_preempt_state);
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rcu_cleanup_dying_cpu(&rcu_preempt_state);
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}
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/*
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@ -1052,16 +1053,16 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
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return 0;
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}
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#endif /* #ifdef CONFIG_HOTPLUG_CPU */
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/*
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* Because preemptible RCU does not exist, it never needs CPU-offline
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* processing.
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*/
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static void rcu_preempt_offline_cpu(int cpu)
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static void rcu_preempt_cleanup_dead_cpu(int cpu)
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{
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}
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#endif /* #ifdef CONFIG_HOTPLUG_CPU */
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/*
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* Because preemptible RCU does not exist, it never has any callbacks
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* to check.
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@ -1153,9 +1154,9 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
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}
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/*
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* Because there is no preemptible RCU, there are no callbacks to move.
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* Because there is no preemptible RCU, there is no cleanup to do.
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*/
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static void rcu_preempt_send_cbs_to_online(void)
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static void rcu_preempt_cleanup_dying_cpu(void)
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{
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}
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