/* SPDX-License-Identifier: GPL-2.0+ */ /* * Read-Copy Update mechanism for mutual exclusion (tree-based version) * Internal non-public definitions. * * Copyright IBM Corporation, 2008 * * Author: Ingo Molnar <mingo@elte.hu> * Paul E. McKenney <paulmck@linux.ibm.com> */ #include <linux/cache.h> #include <linux/kthread.h> #include <linux/spinlock.h> #include <linux/rtmutex.h> #include <linux/threads.h> #include <linux/cpumask.h> #include <linux/seqlock.h> #include <linux/swait.h> #include <linux/rcu_node_tree.h> #include "rcu_segcblist.h" /* Communicate arguments to a kthread worker handler. */ struct rcu_exp_work { unsigned long rew_s; struct kthread_work rew_work; }; /* RCU's kthread states for tracing. */ #define RCU_KTHREAD_STOPPED 0 #define RCU_KTHREAD_RUNNING 1 #define RCU_KTHREAD_WAITING 2 #define RCU_KTHREAD_OFFCPU 3 #define RCU_KTHREAD_YIELDING 4 #define RCU_KTHREAD_MAX 4 /* * Definition for node within the RCU grace-period-detection hierarchy. */ struct rcu_node { raw_spinlock_t __private lock; /* Root rcu_node's lock protects */ /* some rcu_state fields as well as */ /* following. */ unsigned long gp_seq; /* Track rsp->gp_seq. */ unsigned long gp_seq_needed; /* Track furthest future GP request. */ unsigned long completedqs; /* All QSes done for this node. */ unsigned long qsmask; /* CPUs or groups that need to switch in */ /* order for current grace period to proceed.*/ /* In leaf rcu_node, each bit corresponds to */ /* an rcu_data structure, otherwise, each */ /* bit corresponds to a child rcu_node */ /* structure. */ unsigned long rcu_gp_init_mask; /* Mask of offline CPUs at GP init. */ unsigned long qsmaskinit; /* Per-GP initial value for qsmask. */ /* Initialized from ->qsmaskinitnext at the */ /* beginning of each grace period. */ unsigned long qsmaskinitnext; unsigned long expmask; /* CPUs or groups that need to check in */ /* to allow the current expedited GP */ /* to complete. */ unsigned long expmaskinit; /* Per-GP initial values for expmask. */ /* Initialized from ->expmaskinitnext at the */ /* beginning of each expedited GP. */ unsigned long expmaskinitnext; /* Online CPUs for next expedited GP. */ /* Any CPU that has ever been online will */ /* have its bit set. */ struct kthread_worker *exp_kworker; /* Workers performing per node expedited GP */ /* initialization. */ unsigned long cbovldmask; /* CPUs experiencing callback overload. */ unsigned long ffmask; /* Fully functional CPUs. */ unsigned long grpmask; /* Mask to apply to parent qsmask. */ /* Only one bit will be set in this mask. */ int grplo; /* lowest-numbered CPU here. */ int grphi; /* highest-numbered CPU here. */ u8 grpnum; /* group number for next level up. */ u8 level; /* root is at level 0. */ bool wait_blkd_tasks;/* Necessary to wait for blocked tasks to */ /* exit RCU read-side critical sections */ /* before propagating offline up the */ /* rcu_node tree? */ struct rcu_node *parent; struct list_head blkd_tasks; /* Tasks blocked in RCU read-side critical */ /* section. Tasks are placed at the head */ /* of this list and age towards the tail. */ struct list_head *gp_tasks; /* Pointer to the first task blocking the */ /* current grace period, or NULL if there */ /* is no such task. */ struct list_head *exp_tasks; /* Pointer to the first task blocking the */ /* current expedited grace period, or NULL */ /* if there is no such task. If there */ /* is no current expedited grace period, */ /* then there can cannot be any such task. */ struct list_head *boost_tasks; /* Pointer to first task that needs to be */ /* priority boosted, or NULL if no priority */ /* boosting is needed for this rcu_node */ /* structure. If there are no tasks */ /* queued on this rcu_node structure that */ /* are blocking the current grace period, */ /* there can be no such task. */ struct rt_mutex boost_mtx; /* Used only for the priority-boosting */ /* side effect, not as a lock. */ unsigned long boost_time; /* When to start boosting (jiffies). */ struct mutex kthread_mutex; /* Exclusion for thread spawning and affinity */ /* manipulation. */ struct task_struct *boost_kthread_task; /* kthread that takes care of priority */ /* boosting for this rcu_node structure. */ unsigned int boost_kthread_status; /* State of boost_kthread_task for tracing. */ unsigned long n_boosts; /* Number of boosts for this rcu_node structure. */ #ifdef CONFIG_RCU_NOCB_CPU struct swait_queue_head nocb_gp_wq[2]; /* Place for rcu_nocb_kthread() to wait GP. */ #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp; spinlock_t exp_lock ____cacheline_internodealigned_in_smp; unsigned long exp_seq_rq; wait_queue_head_t exp_wq[4]; struct rcu_exp_work rew; bool exp_need_flush; /* Need to flush workitem? */ raw_spinlock_t exp_poll_lock; /* Lock and data for polled expedited grace periods. */ unsigned long exp_seq_poll_rq; struct work_struct exp_poll_wq; } ____cacheline_internodealigned_in_smp; /* * Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and * are indexed relative to this interval rather than the global CPU ID space. * This generates the bit for a CPU in node-local masks. */ #define leaf_node_cpu_bit(rnp, cpu) (BIT((cpu) - (rnp)->grplo)) /* * Union to allow "aggregate OR" operation on the need for a quiescent * state by the normal and expedited grace periods. */ union rcu_noqs { struct { u8 norm; u8 exp; } b; /* Bits. */ u16 s; /* Set of bits, aggregate OR here. */ }; /* * Record the snapshot of the core stats at half of the first RCU stall timeout. * The member gp_seq is used to ensure that all members are updated only once * during the sampling period. The snapshot is taken only if this gp_seq is not * equal to rdp->gp_seq. */ struct rcu_snap_record { unsigned long gp_seq; /* Track rdp->gp_seq counter */ u64 cputime_irq; /* Accumulated cputime of hard irqs */ u64 cputime_softirq;/* Accumulated cputime of soft irqs */ u64 cputime_system; /* Accumulated cputime of kernel tasks */ u64 nr_hardirqs; /* Accumulated number of hard irqs */ unsigned int nr_softirqs; /* Accumulated number of soft irqs */ unsigned long long nr_csw; /* Accumulated number of task switches */ unsigned long jiffies; /* Track jiffies value */ }; /* * An IRQ work (deferred_qs_iw) is used by RCU to get the scheduler's attention. * to report quiescent states at the soonest possible time. * The request can be in one of the following states: * - DEFER_QS_IDLE: An IRQ work is yet to be scheduled. * - DEFER_QS_PENDING: An IRQ work was scheduled but either not yet run, or it * ran and we still haven't reported a quiescent state. */ #define DEFER_QS_IDLE 0 #define DEFER_QS_PENDING 1 /* Per-CPU data for read-copy update. */ struct rcu_data { /* 1) quiescent-state and grace-period handling : */ unsigned long gp_seq; /* Track rsp->gp_seq counter. */ unsigned long gp_seq_needed; /* Track furthest future GP request. */ union rcu_noqs cpu_no_qs; /* No QSes yet for this CPU. */ bool core_needs_qs; /* Core waits for quiescent state. */ bool beenonline; /* CPU online at least once. */ bool gpwrap; /* Possible ->gp_seq wrap. */ unsigned int gpwrap_count; /* Count of GP sequence wrap. */ bool cpu_started; /* RCU watching this onlining CPU. */ struct rcu_node *mynode; /* This CPU's leaf of hierarchy */ unsigned long grpmask; /* Mask to apply to leaf qsmask. */ unsigned long ticks_this_gp; /* The number of scheduling-clock */ /* ticks this CPU has handled */ /* during and after the last grace */ /* period it is aware of. */ struct irq_work defer_qs_iw; /* Obtain later scheduler attention. */ int defer_qs_pending; /* irqwork or softirq pending? */ struct work_struct strict_work; /* Schedule readers for strict GPs. */ /* 2) batch handling */ struct rcu_segcblist cblist; /* Segmented callback list, with */ /* different callbacks waiting for */ /* different grace periods. */ long qlen_last_fqs_check; /* qlen at last check for QS forcing */ unsigned long n_cbs_invoked; /* # callbacks invoked since boot. */ unsigned long n_force_qs_snap; /* did other CPU force QS recently? */ long blimit; /* Upper limit on a processed batch */ /* 3) dynticks interface. */ int watching_snap; /* Per-GP tracking for dynticks. */ bool rcu_need_heavy_qs; /* GP old, so heavy quiescent state! */ bool rcu_urgent_qs; /* GP old need light quiescent state. */ bool rcu_forced_tick; /* Forced tick to provide QS. */ bool rcu_forced_tick_exp; /* ... provide QS to expedited GP. */ /* 4) rcu_barrier(), OOM callbacks, and expediting. */ unsigned long barrier_seq_snap; /* Snap of rcu_state.barrier_sequence. */ struct rcu_head barrier_head; int exp_watching_snap; /* Double-check need for IPI. */ /* 5) Callback offloading. */ #ifdef CONFIG_RCU_NOCB_CPU struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */ struct swait_queue_head nocb_state_wq; /* For offloading state changes */ struct task_struct *nocb_gp_kthread; raw_spinlock_t nocb_lock; /* Guard following pair of fields. */ int nocb_defer_wakeup; /* Defer wakeup of nocb_kthread. */ struct timer_list nocb_timer; /* Enforce finite deferral. */ unsigned long nocb_gp_adv_time; /* Last call_rcu() CB adv (jiffies). */ struct mutex nocb_gp_kthread_mutex; /* Exclusion for nocb gp kthread */ /* spawning */ /* The following fields are used by call_rcu, hence own cacheline. */ raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp; struct rcu_cblist nocb_bypass; /* Lock-contention-bypass CB list. */ unsigned long nocb_bypass_first; /* Time (jiffies) of first enqueue. */ unsigned long nocb_nobypass_last; /* Last ->cblist enqueue (jiffies). */ int nocb_nobypass_count; /* # ->cblist enqueues at ^^^ time. */ /* The following fields are used by GP kthread, hence own cacheline. */ raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp; u8 nocb_gp_sleep; /* Is the nocb GP thread asleep? */ u8 nocb_gp_bypass; /* Found a bypass on last scan? */ u8 nocb_gp_gp; /* GP to wait for on last scan? */ unsigned long nocb_gp_seq; /* If so, ->gp_seq to wait for. */ unsigned long nocb_gp_loops; /* # passes through wait code. */ struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */ bool nocb_cb_sleep; /* Is the nocb CB thread asleep? */ struct task_struct *nocb_cb_kthread; struct list_head nocb_head_rdp; /* * Head of rcu_data list in wakeup chain, * if rdp_gp. */ struct list_head nocb_entry_rdp; /* rcu_data node in wakeup chain. */ struct rcu_data *nocb_toggling_rdp; /* rdp queued for (de-)offloading */ /* The following fields are used by CB kthread, hence new cacheline. */ struct rcu_data *nocb_gp_rdp ____cacheline_internodealigned_in_smp; /* GP rdp takes GP-end wakeups. */ #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ /* 6) RCU priority boosting. */ struct task_struct *rcu_cpu_kthread_task; /* rcuc per-CPU kthread or NULL. */ unsigned int rcu_cpu_kthread_status; char rcu_cpu_has_work; unsigned long rcuc_activity; /* 7) Diagnostic data, including RCU CPU stall warnings. */ unsigned int softirq_snap; /* Snapshot of softirq activity. */ /* ->rcu_iw* fields protected by leaf rcu_node ->lock. */ struct irq_work rcu_iw; /* Check for non-irq activity. */ bool rcu_iw_pending; /* Is ->rcu_iw pending? */ unsigned long rcu_iw_gp_seq; /* ->gp_seq associated with ->rcu_iw. */ unsigned long rcu_ofl_gp_seq; /* ->gp_seq at last offline. */ short rcu_ofl_gp_state; /* ->gp_state at last offline. */ unsigned long rcu_onl_gp_seq; /* ->gp_seq at last online. */ short rcu_onl_gp_state; /* ->gp_state at last online. */ unsigned long last_fqs_resched; /* Time of last rcu_resched(). */ unsigned long last_sched_clock; /* Jiffies of last rcu_sched_clock_irq(). */ struct rcu_snap_record snap_record; /* Snapshot of core stats at half of */ /* the first RCU stall timeout */ long lazy_len; /* Length of buffered lazy callbacks. */ int cpu; }; /* Values for nocb_defer_wakeup field in struct rcu_data. */ #define RCU_NOCB_WAKE_NOT 0 #define RCU_NOCB_WAKE_BYPASS 1 #define RCU_NOCB_WAKE_LAZY 2 #define RCU_NOCB_WAKE 3 #define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500)) /* For jiffies_till_first_fqs and */ /* and jiffies_till_next_fqs. */ #define RCU_JIFFIES_FQS_DIV 256 /* Very large systems need more */ /* delay between bouts of */ /* quiescent-state forcing. */ #define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time to take */ /* at least one scheduling clock */ /* irq before ratting on them. */ #define rcu_wait(cond) \ do { \ for (;;) { \ set_current_state(TASK_INTERRUPTIBLE); \ if (cond) \ break; \ schedule(); \ } \ __set_current_state(TASK_RUNNING); \ } while (0) /* * A max threshold for synchronize_rcu() users which are * awaken directly by the rcu_gp_kthread(). Left part is * deferred to the main worker. */ #define SR_MAX_USERS_WAKE_FROM_GP 5 #define SR_NORMAL_GP_WAIT_HEAD_MAX 5 struct sr_wait_node { atomic_t inuse; struct llist_node node; }; /* * RCU global state, including node hierarchy. This hierarchy is * represented in "heap" form in a dense array. The root (first level) * of the hierarchy is in ->node[0] (referenced by ->level[0]), the second * level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]), * and the third level in ->node[m+1] and following (->node[m+1] referenced * by ->level[2]). The number of levels is determined by the number of * CPUs and by CONFIG_RCU_FANOUT. Small systems will have a "hierarchy" * consisting of a single rcu_node. */ struct rcu_state { struct rcu_node node[NUM_RCU_NODES]; /* Hierarchy. */ struct rcu_node *level[RCU_NUM_LVLS + 1]; /* Hierarchy levels (+1 to */ /* shut bogus gcc warning) */ int ncpus; /* # CPUs seen so far. */ int n_online_cpus; /* # CPUs online for RCU. */ /* The following fields are guarded by the root rcu_node's lock. */ unsigned long gp_seq ____cacheline_internodealigned_in_smp; /* Grace-period sequence #. */ unsigned long gp_max; /* Maximum GP duration in */ /* jiffies. */ struct task_struct *gp_kthread; /* Task for grace periods. */ struct swait_queue_head gp_wq; /* Where GP task waits. */ short gp_flags; /* Commands for GP task. */ short gp_state; /* GP kthread sleep state. */ unsigned long gp_wake_time; /* Last GP kthread wake. */ unsigned long gp_wake_seq; /* ->gp_seq at ^^^. */ unsigned long gp_seq_polled; /* GP seq for polled API. */ unsigned long gp_seq_polled_snap; /* ->gp_seq_polled at normal GP start. */ unsigned long gp_seq_polled_exp_snap; /* ->gp_seq_polled at expedited GP start. */ /* End of fields guarded by root rcu_node's lock. */ struct mutex barrier_mutex; /* Guards barrier fields. */ atomic_t barrier_cpu_count; /* # CPUs waiting on. */ struct completion barrier_completion; /* Wake at barrier end. */ unsigned long barrier_sequence; /* ++ at start and end of */ /* rcu_barrier(). */ /* End of fields guarded by barrier_mutex. */ raw_spinlock_t barrier_lock; /* Protects ->barrier_seq_snap. */ struct mutex exp_mutex; /* Serialize expedited GP. */ struct mutex exp_wake_mutex; /* Serialize wakeup. */ unsigned long expedited_sequence; /* Take a ticket. */ atomic_t expedited_need_qs; /* # CPUs left to check in. */ struct swait_queue_head expedited_wq; /* Wait for check-ins. */ int ncpus_snap; /* # CPUs seen last time. */ u8 cbovld; /* Callback overload now? */ u8 cbovldnext; /* ^ ^ next time? */ unsigned long jiffies_force_qs; /* Time at which to invoke */ /* force_quiescent_state(). */ unsigned long jiffies_kick_kthreads; /* Time at which to kick */ /* kthreads, if configured. */ unsigned long n_force_qs; /* Number of calls to */ /* force_quiescent_state(). */ unsigned long gp_start; /* Time at which GP started, */ /* but in jiffies. */ unsigned long gp_end; /* Time last GP ended, again */ /* in jiffies. */ unsigned long gp_activity; /* Time of last GP kthread */ /* activity in jiffies. */ unsigned long gp_req_activity; /* Time of last GP request */ /* in jiffies. */ unsigned long jiffies_stall; /* Time at which to check */ /* for CPU stalls. */ int nr_fqs_jiffies_stall; /* Number of fqs loops after * which read jiffies and set * jiffies_stall. Stall * warnings disabled if !0. */ unsigned long jiffies_resched; /* Time at which to resched */ /* a reluctant CPU. */ unsigned long n_force_qs_gpstart; /* Snapshot of n_force_qs at */ /* GP start. */ const char *name; /* Name of structure. */ char abbr; /* Abbreviated name. */ arch_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp; /* Synchronize offline with */ /* GP pre-initialization. */ /* synchronize_rcu() part. */ struct llist_head srs_next; /* request a GP users. */ struct llist_node *srs_wait_tail; /* wait for GP users. */ struct llist_node *srs_done_tail; /* ready for GP users. */ struct sr_wait_node srs_wait_nodes[SR_NORMAL_GP_WAIT_HEAD_MAX]; struct work_struct srs_cleanup_work; atomic_t srs_cleanups_pending; /* srs inflight worker cleanups. */ #ifdef CONFIG_RCU_NOCB_CPU struct mutex nocb_mutex; /* Guards (de-)offloading */ int nocb_is_setup; /* nocb is setup from boot */ #endif }; /* Values for rcu_state structure's gp_flags field. */ #define RCU_GP_FLAG_INIT 0x1 /* Need grace-period initialization. */ #define RCU_GP_FLAG_FQS 0x2 /* Need grace-period quiescent-state forcing. */ #define RCU_GP_FLAG_OVLD 0x4 /* Experiencing callback overload. */ /* Values for rcu_state structure's gp_state field. */ #define RCU_GP_IDLE 0 /* Initial state and no GP in progress. */ #define RCU_GP_WAIT_GPS 1 /* Wait for grace-period start. */ #define RCU_GP_DONE_GPS 2 /* Wait done for grace-period start. */ #define RCU_GP_ONOFF 3 /* Grace-period initialization hotplug. */ #define RCU_GP_INIT 4 /* Grace-period initialization. */ #define RCU_GP_WAIT_FQS 5 /* Wait for force-quiescent-state time. */ #define RCU_GP_DOING_FQS 6 /* Wait done for force-quiescent-state time. */ #define RCU_GP_CLEANUP 7 /* Grace-period cleanup started. */ #define RCU_GP_CLEANED 8 /* Grace-period cleanup complete. */ /* * In order to export the rcu_state name to the tracing tools, it * needs to be added in the __tracepoint_string section. * This requires defining a separate variable tp_<sname>_varname * that points to the string being used, and this will allow * the tracing userspace tools to be able to decipher the string * address to the matching string. */ #ifdef CONFIG_PREEMPT_RCU #define RCU_ABBR 'p' #define RCU_NAME_RAW "rcu_preempt" #else /* #ifdef CONFIG_PREEMPT_RCU */ #define RCU_ABBR 's' #define RCU_NAME_RAW "rcu_sched" #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ #ifndef CONFIG_TRACING #define RCU_NAME RCU_NAME_RAW #else /* #ifdef CONFIG_TRACING */ static char rcu_name[] = RCU_NAME_RAW; static const char *tp_rcu_varname __used __tracepoint_string = rcu_name; #define RCU_NAME rcu_name #endif /* #else #ifdef CONFIG_TRACING */ /* Forward declarations for tree_plugin.h */ static void rcu_bootup_announce(void); static void rcu_qs(void); static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp); #ifdef CONFIG_HOTPLUG_CPU static bool rcu_preempt_has_tasks(struct rcu_node *rnp); #endif /* #ifdef CONFIG_HOTPLUG_CPU */ static int rcu_print_task_exp_stall(struct rcu_node *rnp); static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp); static void rcu_flavor_sched_clock_irq(int user); static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck); static void rcu_preempt_deferred_qs_init(struct rcu_data *rdp); static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags); static void rcu_preempt_boost_start_gp(struct rcu_node *rnp); static bool rcu_is_callbacks_kthread(struct rcu_data *rdp); static void rcu_cpu_kthread_setup(unsigned int cpu); static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp); static bool rcu_preempt_has_tasks(struct rcu_node *rnp); static bool rcu_preempt_need_deferred_qs(struct task_struct *t); static void zero_cpu_stall_ticks(struct rcu_data *rdp); static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp); static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq); static void rcu_init_one_nocb(struct rcu_node *rnp); static bool wake_nocb_gp(struct rcu_data *rdp); static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, unsigned long j, bool lazy); static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head, rcu_callback_t func, unsigned long flags, bool lazy); static void __maybe_unused __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty, unsigned long flags); static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level); static bool do_nocb_deferred_wakeup(struct rcu_data *rdp); static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp); static void rcu_spawn_cpu_nocb_kthread(int cpu); static void show_rcu_nocb_state(struct rcu_data *rdp); static void rcu_nocb_lock(struct rcu_data *rdp); static void rcu_nocb_unlock(struct rcu_data *rdp); static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, unsigned long flags); static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp); #ifdef CONFIG_RCU_NOCB_CPU static void __init rcu_organize_nocb_kthreads(void); /* * Disable IRQs before checking offloaded state so that local * locking is safe against concurrent de-offloading. */ #define rcu_nocb_lock_irqsave(rdp, flags) \ do { \ local_irq_save(flags); \ if (rcu_segcblist_is_offloaded(&(rdp)->cblist)) \ raw_spin_lock(&(rdp)->nocb_lock); \ } while (0) #else /* #ifdef CONFIG_RCU_NOCB_CPU */ #define rcu_nocb_lock_irqsave(rdp, flags) local_irq_save(flags) #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ static void rcu_bind_gp_kthread(void); static bool rcu_nohz_full_cpu(void); /* Forward declarations for tree_stall.h */ static void record_gp_stall_check_time(void); static void rcu_iw_handler(struct irq_work *iwp); static void check_cpu_stall(struct rcu_data *rdp); static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, const unsigned long gpssdelay); /* Forward declarations for tree_exp.h. */ static void sync_rcu_do_polled_gp(struct work_struct *wp);
