diff options
Diffstat (limited to 'kernel/rcu/srcutree.c')
| -rw-r--r-- | kernel/rcu/srcutree.c | 1451 |
1 files changed, 1451 insertions, 0 deletions
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c new file mode 100644 index 000000000..b8821665c --- /dev/null +++ b/kernel/rcu/srcutree.c @@ -0,0 +1,1451 @@ +// SPDX-License-Identifier: GPL-2.0+ +/* + * Sleepable Read-Copy Update mechanism for mutual exclusion. + * + * Copyright (C) IBM Corporation, 2006 + * Copyright (C) Fujitsu, 2012 + * + * Authors: Paul McKenney <paulmck@linux.ibm.com> + * Lai Jiangshan <laijs@cn.fujitsu.com> + * + * For detailed explanation of Read-Copy Update mechanism see - + * Documentation/RCU/ *.txt + * + */ + +#define pr_fmt(fmt) "rcu: " fmt + +#include <linux/export.h> +#include <linux/mutex.h> +#include <linux/percpu.h> +#include <linux/preempt.h> +#include <linux/rcupdate_wait.h> +#include <linux/sched.h> +#include <linux/smp.h> +#include <linux/delay.h> +#include <linux/module.h> +#include <linux/srcu.h> + +#include "rcu.h" +#include "rcu_segcblist.h" + +/* Holdoff in nanoseconds for auto-expediting. */ +#define DEFAULT_SRCU_EXP_HOLDOFF (25 * 1000) +static ulong exp_holdoff = DEFAULT_SRCU_EXP_HOLDOFF; +module_param(exp_holdoff, ulong, 0444); + +/* Overflow-check frequency. N bits roughly says every 2**N grace periods. */ +static ulong counter_wrap_check = (ULONG_MAX >> 2); +module_param(counter_wrap_check, ulong, 0444); + +/* Early-boot callback-management, so early that no lock is required! */ +static LIST_HEAD(srcu_boot_list); +static bool __read_mostly srcu_init_done; + +static void srcu_invoke_callbacks(struct work_struct *work); +static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay); +static void process_srcu(struct work_struct *work); +static void srcu_delay_timer(struct timer_list *t); + +/* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */ +#define spin_lock_rcu_node(p) \ +do { \ + spin_lock(&ACCESS_PRIVATE(p, lock)); \ + smp_mb__after_unlock_lock(); \ +} while (0) + +#define spin_unlock_rcu_node(p) spin_unlock(&ACCESS_PRIVATE(p, lock)) + +#define spin_lock_irq_rcu_node(p) \ +do { \ + spin_lock_irq(&ACCESS_PRIVATE(p, lock)); \ + smp_mb__after_unlock_lock(); \ +} while (0) + +#define spin_unlock_irq_rcu_node(p) \ + spin_unlock_irq(&ACCESS_PRIVATE(p, lock)) + +#define spin_lock_irqsave_rcu_node(p, flags) \ +do { \ + spin_lock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \ + smp_mb__after_unlock_lock(); \ +} while (0) + +#define spin_unlock_irqrestore_rcu_node(p, flags) \ + spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) \ + +/* + * Initialize SRCU combining tree. Note that statically allocated + * srcu_struct structures might already have srcu_read_lock() and + * srcu_read_unlock() running against them. So if the is_static parameter + * is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[]. + */ +static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static) +{ + int cpu; + int i; + int level = 0; + int levelspread[RCU_NUM_LVLS]; + struct srcu_data *sdp; + struct srcu_node *snp; + struct srcu_node *snp_first; + + /* Initialize geometry if it has not already been initialized. */ + rcu_init_geometry(); + + /* Work out the overall tree geometry. */ + ssp->level[0] = &ssp->node[0]; + for (i = 1; i < rcu_num_lvls; i++) + ssp->level[i] = ssp->level[i - 1] + num_rcu_lvl[i - 1]; + rcu_init_levelspread(levelspread, num_rcu_lvl); + + /* Each pass through this loop initializes one srcu_node structure. */ + srcu_for_each_node_breadth_first(ssp, snp) { + spin_lock_init(&ACCESS_PRIVATE(snp, lock)); + WARN_ON_ONCE(ARRAY_SIZE(snp->srcu_have_cbs) != + ARRAY_SIZE(snp->srcu_data_have_cbs)); + for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++) { + snp->srcu_have_cbs[i] = 0; + snp->srcu_data_have_cbs[i] = 0; + } + snp->srcu_gp_seq_needed_exp = 0; + snp->grplo = -1; + snp->grphi = -1; + if (snp == &ssp->node[0]) { + /* Root node, special case. */ + snp->srcu_parent = NULL; + continue; + } + + /* Non-root node. */ + if (snp == ssp->level[level + 1]) + level++; + snp->srcu_parent = ssp->level[level - 1] + + (snp - ssp->level[level]) / + levelspread[level - 1]; + } + + /* + * Initialize the per-CPU srcu_data array, which feeds into the + * leaves of the srcu_node tree. + */ + WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) != + ARRAY_SIZE(sdp->srcu_unlock_count)); + level = rcu_num_lvls - 1; + snp_first = ssp->level[level]; + for_each_possible_cpu(cpu) { + sdp = per_cpu_ptr(ssp->sda, cpu); + spin_lock_init(&ACCESS_PRIVATE(sdp, lock)); + rcu_segcblist_init(&sdp->srcu_cblist); + sdp->srcu_cblist_invoking = false; + sdp->srcu_gp_seq_needed = ssp->srcu_gp_seq; + sdp->srcu_gp_seq_needed_exp = ssp->srcu_gp_seq; + sdp->mynode = &snp_first[cpu / levelspread[level]]; + for (snp = sdp->mynode; snp != NULL; snp = snp->srcu_parent) { + if (snp->grplo < 0) + snp->grplo = cpu; + snp->grphi = cpu; + } + sdp->cpu = cpu; + INIT_WORK(&sdp->work, srcu_invoke_callbacks); + timer_setup(&sdp->delay_work, srcu_delay_timer, 0); + sdp->ssp = ssp; + sdp->grpmask = 1 << (cpu - sdp->mynode->grplo); + if (is_static) + continue; + + /* Dynamically allocated, better be no srcu_read_locks()! */ + for (i = 0; i < ARRAY_SIZE(sdp->srcu_lock_count); i++) { + sdp->srcu_lock_count[i] = 0; + sdp->srcu_unlock_count[i] = 0; + } + } +} + +/* + * Initialize non-compile-time initialized fields, including the + * associated srcu_node and srcu_data structures. The is_static + * parameter is passed through to init_srcu_struct_nodes(), and + * also tells us that ->sda has already been wired up to srcu_data. + */ +static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) +{ + mutex_init(&ssp->srcu_cb_mutex); + mutex_init(&ssp->srcu_gp_mutex); + ssp->srcu_idx = 0; + ssp->srcu_gp_seq = 0; + ssp->srcu_barrier_seq = 0; + mutex_init(&ssp->srcu_barrier_mutex); + atomic_set(&ssp->srcu_barrier_cpu_cnt, 0); + INIT_DELAYED_WORK(&ssp->work, process_srcu); + if (!is_static) + ssp->sda = alloc_percpu(struct srcu_data); + init_srcu_struct_nodes(ssp, is_static); + ssp->srcu_gp_seq_needed_exp = 0; + ssp->srcu_last_gp_end = ktime_get_mono_fast_ns(); + smp_store_release(&ssp->srcu_gp_seq_needed, 0); /* Init done. */ + return ssp->sda ? 0 : -ENOMEM; +} + +#ifdef CONFIG_DEBUG_LOCK_ALLOC + +int __init_srcu_struct(struct srcu_struct *ssp, const char *name, + struct lock_class_key *key) +{ + /* Don't re-initialize a lock while it is held. */ + debug_check_no_locks_freed((void *)ssp, sizeof(*ssp)); + lockdep_init_map(&ssp->dep_map, name, key, 0); + spin_lock_init(&ACCESS_PRIVATE(ssp, lock)); + return init_srcu_struct_fields(ssp, false); +} +EXPORT_SYMBOL_GPL(__init_srcu_struct); + +#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ + +/** + * init_srcu_struct - initialize a sleep-RCU structure + * @ssp: structure to initialize. + * + * Must invoke this on a given srcu_struct before passing that srcu_struct + * to any other function. Each srcu_struct represents a separate domain + * of SRCU protection. + */ +int init_srcu_struct(struct srcu_struct *ssp) +{ + spin_lock_init(&ACCESS_PRIVATE(ssp, lock)); + return init_srcu_struct_fields(ssp, false); +} +EXPORT_SYMBOL_GPL(init_srcu_struct); + +#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ + +/* + * First-use initialization of statically allocated srcu_struct + * structure. Wiring up the combining tree is more than can be + * done with compile-time initialization, so this check is added + * to each update-side SRCU primitive. Use ssp->lock, which -is- + * compile-time initialized, to resolve races involving multiple + * CPUs trying to garner first-use privileges. + */ +static void check_init_srcu_struct(struct srcu_struct *ssp) +{ + unsigned long flags; + + /* The smp_load_acquire() pairs with the smp_store_release(). */ + if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_gp_seq_needed))) /*^^^*/ + return; /* Already initialized. */ + spin_lock_irqsave_rcu_node(ssp, flags); + if (!rcu_seq_state(ssp->srcu_gp_seq_needed)) { + spin_unlock_irqrestore_rcu_node(ssp, flags); + return; + } + init_srcu_struct_fields(ssp, true); + spin_unlock_irqrestore_rcu_node(ssp, flags); +} + +/* + * Returns approximate total of the readers' ->srcu_lock_count[] values + * for the rank of per-CPU counters specified by idx. + */ +static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx) +{ + int cpu; + unsigned long sum = 0; + + for_each_possible_cpu(cpu) { + struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); + + sum += READ_ONCE(cpuc->srcu_lock_count[idx]); + } + return sum; +} + +/* + * Returns approximate total of the readers' ->srcu_unlock_count[] values + * for the rank of per-CPU counters specified by idx. + */ +static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx) +{ + int cpu; + unsigned long sum = 0; + + for_each_possible_cpu(cpu) { + struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); + + sum += READ_ONCE(cpuc->srcu_unlock_count[idx]); + } + return sum; +} + +/* + * Return true if the number of pre-existing readers is determined to + * be zero. + */ +static bool srcu_readers_active_idx_check(struct srcu_struct *ssp, int idx) +{ + unsigned long unlocks; + + unlocks = srcu_readers_unlock_idx(ssp, idx); + + /* + * Make sure that a lock is always counted if the corresponding + * unlock is counted. Needs to be a smp_mb() as the read side may + * contain a read from a variable that is written to before the + * synchronize_srcu() in the write side. In this case smp_mb()s + * A and B act like the store buffering pattern. + * + * This smp_mb() also pairs with smp_mb() C to prevent accesses + * after the synchronize_srcu() from being executed before the + * grace period ends. + */ + smp_mb(); /* A */ + + /* + * If the locks are the same as the unlocks, then there must have + * been no readers on this index at some time in between. This does + * not mean that there are no more readers, as one could have read + * the current index but not have incremented the lock counter yet. + * + * So suppose that the updater is preempted here for so long + * that more than ULONG_MAX non-nested readers come and go in + * the meantime. It turns out that this cannot result in overflow + * because if a reader modifies its unlock count after we read it + * above, then that reader's next load of ->srcu_idx is guaranteed + * to get the new value, which will cause it to operate on the + * other bank of counters, where it cannot contribute to the + * overflow of these counters. This means that there is a maximum + * of 2*NR_CPUS increments, which cannot overflow given current + * systems, especially not on 64-bit systems. + * + * OK, how about nesting? This does impose a limit on nesting + * of floor(ULONG_MAX/NR_CPUS/2), which should be sufficient, + * especially on 64-bit systems. + */ + return srcu_readers_lock_idx(ssp, idx) == unlocks; +} + +/** + * srcu_readers_active - returns true if there are readers. and false + * otherwise + * @ssp: which srcu_struct to count active readers (holding srcu_read_lock). + * + * Note that this is not an atomic primitive, and can therefore suffer + * severe errors when invoked on an active srcu_struct. That said, it + * can be useful as an error check at cleanup time. + */ +static bool srcu_readers_active(struct srcu_struct *ssp) +{ + int cpu; + unsigned long sum = 0; + + for_each_possible_cpu(cpu) { + struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); + + sum += READ_ONCE(cpuc->srcu_lock_count[0]); + sum += READ_ONCE(cpuc->srcu_lock_count[1]); + sum -= READ_ONCE(cpuc->srcu_unlock_count[0]); + sum -= READ_ONCE(cpuc->srcu_unlock_count[1]); + } + return sum; +} + +#define SRCU_INTERVAL 1 + +/* + * Return grace-period delay, zero if there are expedited grace + * periods pending, SRCU_INTERVAL otherwise. + */ +static unsigned long srcu_get_delay(struct srcu_struct *ssp) +{ + if (ULONG_CMP_LT(READ_ONCE(ssp->srcu_gp_seq), + READ_ONCE(ssp->srcu_gp_seq_needed_exp))) + return 0; + return SRCU_INTERVAL; +} + +/** + * cleanup_srcu_struct - deconstruct a sleep-RCU structure + * @ssp: structure to clean up. + * + * Must invoke this after you are finished using a given srcu_struct that + * was initialized via init_srcu_struct(), else you leak memory. + */ +void cleanup_srcu_struct(struct srcu_struct *ssp) +{ + int cpu; + + if (WARN_ON(!srcu_get_delay(ssp))) + return; /* Just leak it! */ + if (WARN_ON(srcu_readers_active(ssp))) + return; /* Just leak it! */ + flush_delayed_work(&ssp->work); + for_each_possible_cpu(cpu) { + struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu); + + del_timer_sync(&sdp->delay_work); + flush_work(&sdp->work); + if (WARN_ON(rcu_segcblist_n_cbs(&sdp->srcu_cblist))) + return; /* Forgot srcu_barrier(), so just leak it! */ + } + if (WARN_ON(rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) != SRCU_STATE_IDLE) || + WARN_ON(srcu_readers_active(ssp))) { + pr_info("%s: Active srcu_struct %p state: %d\n", + __func__, ssp, rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq))); + return; /* Caller forgot to stop doing call_srcu()? */ + } + free_percpu(ssp->sda); + ssp->sda = NULL; +} +EXPORT_SYMBOL_GPL(cleanup_srcu_struct); + +/* + * Counts the new reader in the appropriate per-CPU element of the + * srcu_struct. + * Returns an index that must be passed to the matching srcu_read_unlock(). + */ +int __srcu_read_lock(struct srcu_struct *ssp) +{ + int idx; + + idx = READ_ONCE(ssp->srcu_idx) & 0x1; + this_cpu_inc(ssp->sda->srcu_lock_count[idx]); + smp_mb(); /* B */ /* Avoid leaking the critical section. */ + return idx; +} +EXPORT_SYMBOL_GPL(__srcu_read_lock); + +/* + * Removes the count for the old reader from the appropriate per-CPU + * element of the srcu_struct. Note that this may well be a different + * CPU than that which was incremented by the corresponding srcu_read_lock(). + */ +void __srcu_read_unlock(struct srcu_struct *ssp, int idx) +{ + smp_mb(); /* C */ /* Avoid leaking the critical section. */ + this_cpu_inc(ssp->sda->srcu_unlock_count[idx]); +} +EXPORT_SYMBOL_GPL(__srcu_read_unlock); + +/* + * We use an adaptive strategy for synchronize_srcu() and especially for + * synchronize_srcu_expedited(). We spin for a fixed time period + * (defined below) to allow SRCU readers to exit their read-side critical + * sections. If there are still some readers after a few microseconds, + * we repeatedly block for 1-millisecond time periods. + */ +#define SRCU_RETRY_CHECK_DELAY 5 + +/* + * Start an SRCU grace period. + */ +static void srcu_gp_start(struct srcu_struct *ssp) +{ + struct srcu_data *sdp = this_cpu_ptr(ssp->sda); + int state; + + lockdep_assert_held(&ACCESS_PRIVATE(ssp, lock)); + WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)); + spin_lock_rcu_node(sdp); /* Interrupts already disabled. */ + rcu_segcblist_advance(&sdp->srcu_cblist, + rcu_seq_current(&ssp->srcu_gp_seq)); + (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, + rcu_seq_snap(&ssp->srcu_gp_seq)); + spin_unlock_rcu_node(sdp); /* Interrupts remain disabled. */ + smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */ + rcu_seq_start(&ssp->srcu_gp_seq); + state = rcu_seq_state(ssp->srcu_gp_seq); + WARN_ON_ONCE(state != SRCU_STATE_SCAN1); +} + + +static void srcu_delay_timer(struct timer_list *t) +{ + struct srcu_data *sdp = container_of(t, struct srcu_data, delay_work); + + queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work); +} + +static void srcu_queue_delayed_work_on(struct srcu_data *sdp, + unsigned long delay) +{ + if (!delay) { + queue_work_on(sdp->cpu, rcu_gp_wq, &sdp->work); + return; + } + + timer_reduce(&sdp->delay_work, jiffies + delay); +} + +/* + * Schedule callback invocation for the specified srcu_data structure, + * if possible, on the corresponding CPU. + */ +static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay) +{ + srcu_queue_delayed_work_on(sdp, delay); +} + +/* + * Schedule callback invocation for all srcu_data structures associated + * with the specified srcu_node structure that have callbacks for the + * just-completed grace period, the one corresponding to idx. If possible, + * schedule this invocation on the corresponding CPUs. + */ +static void srcu_schedule_cbs_snp(struct srcu_struct *ssp, struct srcu_node *snp, + unsigned long mask, unsigned long delay) +{ + int cpu; + + for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) { + if (!(mask & (1 << (cpu - snp->grplo)))) + continue; + srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, cpu), delay); + } +} + +/* + * Note the end of an SRCU grace period. Initiates callback invocation + * and starts a new grace period if needed. + * + * The ->srcu_cb_mutex acquisition does not protect any data, but + * instead prevents more than one grace period from starting while we + * are initiating callback invocation. This allows the ->srcu_have_cbs[] + * array to have a finite number of elements. + */ +static void srcu_gp_end(struct srcu_struct *ssp) +{ + unsigned long cbdelay; + bool cbs; + bool last_lvl; + int cpu; + unsigned long flags; + unsigned long gpseq; + int idx; + unsigned long mask; + struct srcu_data *sdp; + struct srcu_node *snp; + + /* Prevent more than one additional grace period. */ + mutex_lock(&ssp->srcu_cb_mutex); + + /* End the current grace period. */ + spin_lock_irq_rcu_node(ssp); + idx = rcu_seq_state(ssp->srcu_gp_seq); + WARN_ON_ONCE(idx != SRCU_STATE_SCAN2); + cbdelay = srcu_get_delay(ssp); + WRITE_ONCE(ssp->srcu_last_gp_end, ktime_get_mono_fast_ns()); + rcu_seq_end(&ssp->srcu_gp_seq); + gpseq = rcu_seq_current(&ssp->srcu_gp_seq); + if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq)) + WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, gpseq); + spin_unlock_irq_rcu_node(ssp); + mutex_unlock(&ssp->srcu_gp_mutex); + /* A new grace period can start at this point. But only one. */ + + /* Initiate callback invocation as needed. */ + idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs); + srcu_for_each_node_breadth_first(ssp, snp) { + spin_lock_irq_rcu_node(snp); + cbs = false; + last_lvl = snp >= ssp->level[rcu_num_lvls - 1]; + if (last_lvl) + cbs = snp->srcu_have_cbs[idx] == gpseq; + snp->srcu_have_cbs[idx] = gpseq; + rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1); + if (ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, gpseq)) + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq); + mask = snp->srcu_data_have_cbs[idx]; + snp->srcu_data_have_cbs[idx] = 0; + spin_unlock_irq_rcu_node(snp); + if (cbs) + srcu_schedule_cbs_snp(ssp, snp, mask, cbdelay); + + /* Occasionally prevent srcu_data counter wrap. */ + if (!(gpseq & counter_wrap_check) && last_lvl) + for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) { + sdp = per_cpu_ptr(ssp->sda, cpu); + spin_lock_irqsave_rcu_node(sdp, flags); + if (ULONG_CMP_GE(gpseq, + sdp->srcu_gp_seq_needed + 100)) + sdp->srcu_gp_seq_needed = gpseq; + if (ULONG_CMP_GE(gpseq, + sdp->srcu_gp_seq_needed_exp + 100)) + sdp->srcu_gp_seq_needed_exp = gpseq; + spin_unlock_irqrestore_rcu_node(sdp, flags); + } + } + + /* Callback initiation done, allow grace periods after next. */ + mutex_unlock(&ssp->srcu_cb_mutex); + + /* Start a new grace period if needed. */ + spin_lock_irq_rcu_node(ssp); + gpseq = rcu_seq_current(&ssp->srcu_gp_seq); + if (!rcu_seq_state(gpseq) && + ULONG_CMP_LT(gpseq, ssp->srcu_gp_seq_needed)) { + srcu_gp_start(ssp); + spin_unlock_irq_rcu_node(ssp); + srcu_reschedule(ssp, 0); + } else { + spin_unlock_irq_rcu_node(ssp); + } +} + +/* + * Funnel-locking scheme to scalably mediate many concurrent expedited + * grace-period requests. This function is invoked for the first known + * expedited request for a grace period that has already been requested, + * but without expediting. To start a completely new grace period, + * whether expedited or not, use srcu_funnel_gp_start() instead. + */ +static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp, + unsigned long s) +{ + unsigned long flags; + + for (; snp != NULL; snp = snp->srcu_parent) { + if (rcu_seq_done(&ssp->srcu_gp_seq, s) || + ULONG_CMP_GE(READ_ONCE(snp->srcu_gp_seq_needed_exp), s)) + return; + spin_lock_irqsave_rcu_node(snp, flags); + if (ULONG_CMP_GE(snp->srcu_gp_seq_needed_exp, s)) { + spin_unlock_irqrestore_rcu_node(snp, flags); + return; + } + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s); + spin_unlock_irqrestore_rcu_node(snp, flags); + } + spin_lock_irqsave_rcu_node(ssp, flags); + if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s)) + WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s); + spin_unlock_irqrestore_rcu_node(ssp, flags); +} + +/* + * Funnel-locking scheme to scalably mediate many concurrent grace-period + * requests. The winner has to do the work of actually starting grace + * period s. Losers must either ensure that their desired grace-period + * number is recorded on at least their leaf srcu_node structure, or they + * must take steps to invoke their own callbacks. + * + * Note that this function also does the work of srcu_funnel_exp_start(), + * in some cases by directly invoking it. + */ +static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp, + unsigned long s, bool do_norm) +{ + unsigned long flags; + int idx = rcu_seq_ctr(s) % ARRAY_SIZE(sdp->mynode->srcu_have_cbs); + struct srcu_node *snp = sdp->mynode; + unsigned long snp_seq; + + /* Each pass through the loop does one level of the srcu_node tree. */ + for (; snp != NULL; snp = snp->srcu_parent) { + if (rcu_seq_done(&ssp->srcu_gp_seq, s) && snp != sdp->mynode) + return; /* GP already done and CBs recorded. */ + spin_lock_irqsave_rcu_node(snp, flags); + if (ULONG_CMP_GE(snp->srcu_have_cbs[idx], s)) { + snp_seq = snp->srcu_have_cbs[idx]; + if (snp == sdp->mynode && snp_seq == s) + snp->srcu_data_have_cbs[idx] |= sdp->grpmask; + spin_unlock_irqrestore_rcu_node(snp, flags); + if (snp == sdp->mynode && snp_seq != s) { + srcu_schedule_cbs_sdp(sdp, do_norm + ? SRCU_INTERVAL + : 0); + return; + } + if (!do_norm) + srcu_funnel_exp_start(ssp, snp, s); + return; + } + snp->srcu_have_cbs[idx] = s; + if (snp == sdp->mynode) + snp->srcu_data_have_cbs[idx] |= sdp->grpmask; + if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s)) + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s); + spin_unlock_irqrestore_rcu_node(snp, flags); + } + + /* Top of tree, must ensure the grace period will be started. */ + spin_lock_irqsave_rcu_node(ssp, flags); + if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed, s)) { + /* + * Record need for grace period s. Pair with load + * acquire setting up for initialization. + */ + smp_store_release(&ssp->srcu_gp_seq_needed, s); /*^^^*/ + } + if (!do_norm && ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s)) + WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s); + + /* If grace period not already done and none in progress, start it. */ + if (!rcu_seq_done(&ssp->srcu_gp_seq, s) && + rcu_seq_state(ssp->srcu_gp_seq) == SRCU_STATE_IDLE) { + WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)); + srcu_gp_start(ssp); + if (likely(srcu_init_done)) + queue_delayed_work(rcu_gp_wq, &ssp->work, + srcu_get_delay(ssp)); + else if (list_empty(&ssp->work.work.entry)) + list_add(&ssp->work.work.entry, &srcu_boot_list); + } + spin_unlock_irqrestore_rcu_node(ssp, flags); +} + +/* + * Wait until all readers counted by array index idx complete, but + * loop an additional time if there is an expedited grace period pending. + * The caller must ensure that ->srcu_idx is not changed while checking. + */ +static bool try_check_zero(struct srcu_struct *ssp, int idx, int trycount) +{ + for (;;) { + if (srcu_readers_active_idx_check(ssp, idx)) + return true; + if (--trycount + !srcu_get_delay(ssp) <= 0) + return false; + udelay(SRCU_RETRY_CHECK_DELAY); + } +} + +/* + * Increment the ->srcu_idx counter so that future SRCU readers will + * use the other rank of the ->srcu_(un)lock_count[] arrays. This allows + * us to wait for pre-existing readers in a starvation-free manner. + */ +static void srcu_flip(struct srcu_struct *ssp) +{ + /* + * Ensure that if this updater saw a given reader's increment + * from __srcu_read_lock(), that reader was using an old value + * of ->srcu_idx. Also ensure that if a given reader sees the + * new value of ->srcu_idx, this updater's earlier scans cannot + * have seen that reader's increments (which is OK, because this + * grace period need not wait on that reader). + */ + smp_mb(); /* E */ /* Pairs with B and C. */ + + WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); + + /* + * Ensure that if the updater misses an __srcu_read_unlock() + * increment, that task's next __srcu_read_lock() will see the + * above counter update. Note that both this memory barrier + * and the one in srcu_readers_active_idx_check() provide the + * guarantee for __srcu_read_lock(). + */ + smp_mb(); /* D */ /* Pairs with C. */ +} + +/* + * If SRCU is likely idle, return true, otherwise return false. + * + * Note that it is OK for several current from-idle requests for a new + * grace period from idle to specify expediting because they will all end + * up requesting the same grace period anyhow. So no loss. + * + * Note also that if any CPU (including the current one) is still invoking + * callbacks, this function will nevertheless say "idle". This is not + * ideal, but the overhead of checking all CPUs' callback lists is even + * less ideal, especially on large systems. Furthermore, the wakeup + * can happen before the callback is fully removed, so we have no choice + * but to accept this type of error. + * + * This function is also subject to counter-wrap errors, but let's face + * it, if this function was preempted for enough time for the counters + * to wrap, it really doesn't matter whether or not we expedite the grace + * period. The extra overhead of a needlessly expedited grace period is + * negligible when amortized over that time period, and the extra latency + * of a needlessly non-expedited grace period is similarly negligible. + */ +static bool srcu_might_be_idle(struct srcu_struct *ssp) +{ + unsigned long curseq; + unsigned long flags; + struct srcu_data *sdp; + unsigned long t; + unsigned long tlast; + + check_init_srcu_struct(ssp); + /* If the local srcu_data structure has callbacks, not idle. */ + sdp = raw_cpu_ptr(ssp->sda); + spin_lock_irqsave_rcu_node(sdp, flags); + if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) { + spin_unlock_irqrestore_rcu_node(sdp, flags); + return false; /* Callbacks already present, so not idle. */ + } + spin_unlock_irqrestore_rcu_node(sdp, flags); + + /* + * No local callbacks, so probabalistically probe global state. + * Exact information would require acquiring locks, which would + * kill scalability, hence the probabalistic nature of the probe. + */ + + /* First, see if enough time has passed since the last GP. */ + t = ktime_get_mono_fast_ns(); + tlast = READ_ONCE(ssp->srcu_last_gp_end); + if (exp_holdoff == 0 || + time_in_range_open(t, tlast, tlast + exp_holdoff)) + return false; /* Too soon after last GP. */ + + /* Next, check for probable idleness. */ + curseq = rcu_seq_current(&ssp->srcu_gp_seq); + smp_mb(); /* Order ->srcu_gp_seq with ->srcu_gp_seq_needed. */ + if (ULONG_CMP_LT(curseq, READ_ONCE(ssp->srcu_gp_seq_needed))) + return false; /* Grace period in progress, so not idle. */ + smp_mb(); /* Order ->srcu_gp_seq with prior access. */ + if (curseq != rcu_seq_current(&ssp->srcu_gp_seq)) + return false; /* GP # changed, so not idle. */ + return true; /* With reasonable probability, idle! */ +} + +/* + * SRCU callback function to leak a callback. + */ +static void srcu_leak_callback(struct rcu_head *rhp) +{ +} + +/* + * Start an SRCU grace period, and also queue the callback if non-NULL. + */ +static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, + struct rcu_head *rhp, bool do_norm) +{ + unsigned long flags; + int idx; + bool needexp = false; + bool needgp = false; + unsigned long s; + struct srcu_data *sdp; + + check_init_srcu_struct(ssp); + idx = srcu_read_lock(ssp); + sdp = raw_cpu_ptr(ssp->sda); + spin_lock_irqsave_rcu_node(sdp, flags); + if (rhp) + rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp); + rcu_segcblist_advance(&sdp->srcu_cblist, + rcu_seq_current(&ssp->srcu_gp_seq)); + s = rcu_seq_snap(&ssp->srcu_gp_seq); + (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s); + if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) { + sdp->srcu_gp_seq_needed = s; + needgp = true; + } + if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) { + sdp->srcu_gp_seq_needed_exp = s; + needexp = true; + } + spin_unlock_irqrestore_rcu_node(sdp, flags); + if (needgp) + srcu_funnel_gp_start(ssp, sdp, s, do_norm); + else if (needexp) + srcu_funnel_exp_start(ssp, sdp->mynode, s); + srcu_read_unlock(ssp, idx); + return s; +} + +/* + * Enqueue an SRCU callback on the srcu_data structure associated with + * the current CPU and the specified srcu_struct structure, initiating + * grace-period processing if it is not already running. + * + * Note that all CPUs must agree that the grace period extended beyond + * all pre-existing SRCU read-side critical section. On systems with + * more than one CPU, this means that when "func()" is invoked, each CPU + * is guaranteed to have executed a full memory barrier since the end of + * its last corresponding SRCU read-side critical section whose beginning + * preceded the call to call_srcu(). It also means that each CPU executing + * an SRCU read-side critical section that continues beyond the start of + * "func()" must have executed a memory barrier after the call_srcu() + * but before the beginning of that SRCU read-side critical section. + * Note that these guarantees include CPUs that are offline, idle, or + * executing in user mode, as well as CPUs that are executing in the kernel. + * + * Furthermore, if CPU A invoked call_srcu() and CPU B invoked the + * resulting SRCU callback function "func()", then both CPU A and CPU + * B are guaranteed to execute a full memory barrier during the time + * interval between the call to call_srcu() and the invocation of "func()". + * This guarantee applies even if CPU A and CPU B are the same CPU (but + * again only if the system has more than one CPU). + * + * Of course, these guarantees apply only for invocations of call_srcu(), + * srcu_read_lock(), and srcu_read_unlock() that are all passed the same + * srcu_struct structure. + */ +static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, + rcu_callback_t func, bool do_norm) +{ + if (debug_rcu_head_queue(rhp)) { + /* Probable double call_srcu(), so leak the callback. */ + WRITE_ONCE(rhp->func, srcu_leak_callback); + WARN_ONCE(1, "call_srcu(): Leaked duplicate callback\n"); + return; + } + rhp->func = func; + (void)srcu_gp_start_if_needed(ssp, rhp, do_norm); +} + +/** + * call_srcu() - Queue a callback for invocation after an SRCU grace period + * @ssp: srcu_struct in queue the callback + * @rhp: structure to be used for queueing the SRCU callback. + * @func: function to be invoked after the SRCU grace period + * + * The callback function will be invoked some time after a full SRCU + * grace period elapses, in other words after all pre-existing SRCU + * read-side critical sections have completed. However, the callback + * function might well execute concurrently with other SRCU read-side + * critical sections that started after call_srcu() was invoked. SRCU + * read-side critical sections are delimited by srcu_read_lock() and + * srcu_read_unlock(), and may be nested. + * + * The callback will be invoked from process context, but must nevertheless + * be fast and must not block. + */ +void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, + rcu_callback_t func) +{ + __call_srcu(ssp, rhp, func, true); +} +EXPORT_SYMBOL_GPL(call_srcu); + +/* + * Helper function for synchronize_srcu() and synchronize_srcu_expedited(). + */ +static void __synchronize_srcu(struct srcu_struct *ssp, bool do_norm) +{ + struct rcu_synchronize rcu; + + RCU_LOCKDEP_WARN(lock_is_held(&ssp->dep_map) || + lock_is_held(&rcu_bh_lock_map) || + lock_is_held(&rcu_lock_map) || + lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section"); + + if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) + return; + might_sleep(); + check_init_srcu_struct(ssp); + init_completion(&rcu.completion); + init_rcu_head_on_stack(&rcu.head); + __call_srcu(ssp, &rcu.head, wakeme_after_rcu, do_norm); + wait_for_completion(&rcu.completion); + destroy_rcu_head_on_stack(&rcu.head); + + /* + * Make sure that later code is ordered after the SRCU grace + * period. This pairs with the spin_lock_irq_rcu_node() + * in srcu_invoke_callbacks(). Unlike Tree RCU, this is needed + * because the current CPU might have been totally uninvolved with + * (and thus unordered against) that grace period. + */ + smp_mb(); +} + +/** + * synchronize_srcu_expedited - Brute-force SRCU grace period + * @ssp: srcu_struct with which to synchronize. + * + * Wait for an SRCU grace period to elapse, but be more aggressive about + * spinning rather than blocking when waiting. + * + * Note that synchronize_srcu_expedited() has the same deadlock and + * memory-ordering properties as does synchronize_srcu(). + */ +void synchronize_srcu_expedited(struct srcu_struct *ssp) +{ + __synchronize_srcu(ssp, rcu_gp_is_normal()); +} +EXPORT_SYMBOL_GPL(synchronize_srcu_expedited); + +/** + * synchronize_srcu - wait for prior SRCU read-side critical-section completion + * @ssp: srcu_struct with which to synchronize. + * + * Wait for the count to drain to zero of both indexes. To avoid the + * possible starvation of synchronize_srcu(), it waits for the count of + * the index=((->srcu_idx & 1) ^ 1) to drain to zero at first, + * and then flip the srcu_idx and wait for the count of the other index. + * + * Can block; must be called from process context. + * + * Note that it is illegal to call synchronize_srcu() from the corresponding + * SRCU read-side critical section; doing so will result in deadlock. + * However, it is perfectly legal to call synchronize_srcu() on one + * srcu_struct from some other srcu_struct's read-side critical section, + * as long as the resulting graph of srcu_structs is acyclic. + * + * There are memory-ordering constraints implied by synchronize_srcu(). + * On systems with more than one CPU, when synchronize_srcu() returns, + * each CPU is guaranteed to have executed a full memory barrier since + * the end of its last corresponding SRCU read-side critical section + * whose beginning preceded the call to synchronize_srcu(). In addition, + * each CPU having an SRCU read-side critical section that extends beyond + * the return from synchronize_srcu() is guaranteed to have executed a + * full memory barrier after the beginning of synchronize_srcu() and before + * the beginning of that SRCU read-side critical section. Note that these + * guarantees include CPUs that are offline, idle, or executing in user mode, + * as well as CPUs that are executing in the kernel. + * + * Furthermore, if CPU A invoked synchronize_srcu(), which returned + * to its caller on CPU B, then both CPU A and CPU B are guaranteed + * to have executed a full memory barrier during the execution of + * synchronize_srcu(). This guarantee applies even if CPU A and CPU B + * are the same CPU, but again only if the system has more than one CPU. + * + * Of course, these memory-ordering guarantees apply only when + * synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are + * passed the same srcu_struct structure. + * + * If SRCU is likely idle, expedite the first request. This semantic + * was provided by Classic SRCU, and is relied upon by its users, so TREE + * SRCU must also provide it. Note that detecting idleness is heuristic + * and subject to both false positives and negatives. + */ +void synchronize_srcu(struct srcu_struct *ssp) +{ + if (srcu_might_be_idle(ssp) || rcu_gp_is_expedited()) + synchronize_srcu_expedited(ssp); + else + __synchronize_srcu(ssp, true); +} +EXPORT_SYMBOL_GPL(synchronize_srcu); + +/** + * get_state_synchronize_srcu - Provide an end-of-grace-period cookie + * @ssp: srcu_struct to provide cookie for. + * + * This function returns a cookie that can be passed to + * poll_state_synchronize_srcu(), which will return true if a full grace + * period has elapsed in the meantime. It is the caller's responsibility + * to make sure that grace period happens, for example, by invoking + * call_srcu() after return from get_state_synchronize_srcu(). + */ +unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp) +{ + // Any prior manipulation of SRCU-protected data must happen + // before the load from ->srcu_gp_seq. + smp_mb(); + return rcu_seq_snap(&ssp->srcu_gp_seq); +} +EXPORT_SYMBOL_GPL(get_state_synchronize_srcu); + +/** + * start_poll_synchronize_srcu - Provide cookie and start grace period + * @ssp: srcu_struct to provide cookie for. + * + * This function returns a cookie that can be passed to + * poll_state_synchronize_srcu(), which will return true if a full grace + * period has elapsed in the meantime. Unlike get_state_synchronize_srcu(), + * this function also ensures that any needed SRCU grace period will be + * started. This convenience does come at a cost in terms of CPU overhead. + */ +unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp) +{ + return srcu_gp_start_if_needed(ssp, NULL, true); +} +EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); + +/** + * poll_state_synchronize_srcu - Has cookie's grace period ended? + * @ssp: srcu_struct to provide cookie for. + * @cookie: Return value from get_state_synchronize_srcu() or start_poll_synchronize_srcu(). + * + * This function takes the cookie that was returned from either + * get_state_synchronize_srcu() or start_poll_synchronize_srcu(), and + * returns @true if an SRCU grace period elapsed since the time that the + * cookie was created. + */ +bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) +{ + if (!rcu_seq_done(&ssp->srcu_gp_seq, cookie)) + return false; + // Ensure that the end of the SRCU grace period happens before + // any subsequent code that the caller might execute. + smp_mb(); // ^^^ + return true; +} +EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu); + +/* + * Callback function for srcu_barrier() use. + */ +static void srcu_barrier_cb(struct rcu_head *rhp) +{ + struct srcu_data *sdp; + struct srcu_struct *ssp; + + sdp = container_of(rhp, struct srcu_data, srcu_barrier_head); + ssp = sdp->ssp; + if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt)) + complete(&ssp->srcu_barrier_completion); +} + +/** + * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete. + * @ssp: srcu_struct on which to wait for in-flight callbacks. + */ +void srcu_barrier(struct srcu_struct *ssp) +{ + int cpu; + struct srcu_data *sdp; + unsigned long s = rcu_seq_snap(&ssp->srcu_barrier_seq); + + check_init_srcu_struct(ssp); + mutex_lock(&ssp->srcu_barrier_mutex); + if (rcu_seq_done(&ssp->srcu_barrier_seq, s)) { + smp_mb(); /* Force ordering following return. */ + mutex_unlock(&ssp->srcu_barrier_mutex); + return; /* Someone else did our work for us. */ + } + rcu_seq_start(&ssp->srcu_barrier_seq); + init_completion(&ssp->srcu_barrier_completion); + + /* Initial count prevents reaching zero until all CBs are posted. */ + atomic_set(&ssp->srcu_barrier_cpu_cnt, 1); + + /* + * Each pass through this loop enqueues a callback, but only + * on CPUs already having callbacks enqueued. Note that if + * a CPU already has callbacks enqueue, it must have already + * registered the need for a future grace period, so all we + * need do is enqueue a callback that will use the same + * grace period as the last callback already in the queue. + */ + for_each_possible_cpu(cpu) { + sdp = per_cpu_ptr(ssp->sda, cpu); + spin_lock_irq_rcu_node(sdp); + atomic_inc(&ssp->srcu_barrier_cpu_cnt); + sdp->srcu_barrier_head.func = srcu_barrier_cb; + debug_rcu_head_queue(&sdp->srcu_barrier_head); + if (!rcu_segcblist_entrain(&sdp->srcu_cblist, + &sdp->srcu_barrier_head)) { + debug_rcu_head_unqueue(&sdp->srcu_barrier_head); + atomic_dec(&ssp->srcu_barrier_cpu_cnt); + } + spin_unlock_irq_rcu_node(sdp); + } + + /* Remove the initial count, at which point reaching zero can happen. */ + if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt)) + complete(&ssp->srcu_barrier_completion); + wait_for_completion(&ssp->srcu_barrier_completion); + + rcu_seq_end(&ssp->srcu_barrier_seq); + mutex_unlock(&ssp->srcu_barrier_mutex); +} +EXPORT_SYMBOL_GPL(srcu_barrier); + +/** + * srcu_batches_completed - return batches completed. + * @ssp: srcu_struct on which to report batch completion. + * + * Report the number of batches, correlated with, but not necessarily + * precisely the same as, the number of grace periods that have elapsed. + */ +unsigned long srcu_batches_completed(struct srcu_struct *ssp) +{ + return READ_ONCE(ssp->srcu_idx); +} +EXPORT_SYMBOL_GPL(srcu_batches_completed); + +/* + * Core SRCU state machine. Push state bits of ->srcu_gp_seq + * to SRCU_STATE_SCAN2, and invoke srcu_gp_end() when scan has + * completed in that state. + */ +static void srcu_advance_state(struct srcu_struct *ssp) +{ + int idx; + + mutex_lock(&ssp->srcu_gp_mutex); + + /* + * Because readers might be delayed for an extended period after + * fetching ->srcu_idx for their index, at any point in time there + * might well be readers using both idx=0 and idx=1. We therefore + * need to wait for readers to clear from both index values before + * invoking a callback. + * + * The load-acquire ensures that we see the accesses performed + * by the prior grace period. + */ + idx = rcu_seq_state(smp_load_acquire(&ssp->srcu_gp_seq)); /* ^^^ */ + if (idx == SRCU_STATE_IDLE) { + spin_lock_irq_rcu_node(ssp); + if (ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)) { + WARN_ON_ONCE(rcu_seq_state(ssp->srcu_gp_seq)); + spin_unlock_irq_rcu_node(ssp); + mutex_unlock(&ssp->srcu_gp_mutex); + return; + } + idx = rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)); + if (idx == SRCU_STATE_IDLE) + srcu_gp_start(ssp); + spin_unlock_irq_rcu_node(ssp); + if (idx != SRCU_STATE_IDLE) { + mutex_unlock(&ssp->srcu_gp_mutex); + return; /* Someone else started the grace period. */ + } + } + + if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN1) { + idx = 1 ^ (ssp->srcu_idx & 1); + if (!try_check_zero(ssp, idx, 1)) { + mutex_unlock(&ssp->srcu_gp_mutex); + return; /* readers present, retry later. */ + } + srcu_flip(ssp); + spin_lock_irq_rcu_node(ssp); + rcu_seq_set_state(&ssp->srcu_gp_seq, SRCU_STATE_SCAN2); + spin_unlock_irq_rcu_node(ssp); + } + + if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN2) { + + /* + * SRCU read-side critical sections are normally short, + * so check at least twice in quick succession after a flip. + */ + idx = 1 ^ (ssp->srcu_idx & 1); + if (!try_check_zero(ssp, idx, 2)) { + mutex_unlock(&ssp->srcu_gp_mutex); + return; /* readers present, retry later. */ + } + srcu_gp_end(ssp); /* Releases ->srcu_gp_mutex. */ + } +} + +/* + * Invoke a limited number of SRCU callbacks that have passed through + * their grace period. If there are more to do, SRCU will reschedule + * the workqueue. Note that needed memory barriers have been executed + * in this task's context by srcu_readers_active_idx_check(). + */ +static void srcu_invoke_callbacks(struct work_struct *work) +{ + bool more; + struct rcu_cblist ready_cbs; + struct rcu_head *rhp; + struct srcu_data *sdp; + struct srcu_struct *ssp; + + sdp = container_of(work, struct srcu_data, work); + + ssp = sdp->ssp; + rcu_cblist_init(&ready_cbs); + spin_lock_irq_rcu_node(sdp); + rcu_segcblist_advance(&sdp->srcu_cblist, + rcu_seq_current(&ssp->srcu_gp_seq)); + if (sdp->srcu_cblist_invoking || + !rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) { + spin_unlock_irq_rcu_node(sdp); + return; /* Someone else on the job or nothing to do. */ + } + + /* We are on the job! Extract and invoke ready callbacks. */ + sdp->srcu_cblist_invoking = true; + rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs); + spin_unlock_irq_rcu_node(sdp); + rhp = rcu_cblist_dequeue(&ready_cbs); + for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) { + debug_rcu_head_unqueue(rhp); + local_bh_disable(); + rhp->func(rhp); + local_bh_enable(); + } + + /* + * Update counts, accelerate new callbacks, and if needed, + * schedule another round of callback invocation. + */ + spin_lock_irq_rcu_node(sdp); + rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs); + (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, + rcu_seq_snap(&ssp->srcu_gp_seq)); + sdp->srcu_cblist_invoking = false; + more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist); + spin_unlock_irq_rcu_node(sdp); + if (more) + srcu_schedule_cbs_sdp(sdp, 0); +} + +/* + * Finished one round of SRCU grace period. Start another if there are + * more SRCU callbacks queued, otherwise put SRCU into not-running state. + */ +static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay) +{ + bool pushgp = true; + + spin_lock_irq_rcu_node(ssp); + if (ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)) { + if (!WARN_ON_ONCE(rcu_seq_state(ssp->srcu_gp_seq))) { + /* All requests fulfilled, time to go idle. */ + pushgp = false; + } + } else if (!rcu_seq_state(ssp->srcu_gp_seq)) { + /* Outstanding request and no GP. Start one. */ + srcu_gp_start(ssp); + } + spin_unlock_irq_rcu_node(ssp); + + if (pushgp) + queue_delayed_work(rcu_gp_wq, &ssp->work, delay); +} + +/* + * This is the work-queue function that handles SRCU grace periods. + */ +static void process_srcu(struct work_struct *work) +{ + struct srcu_struct *ssp; + + ssp = container_of(work, struct srcu_struct, work.work); + + srcu_advance_state(ssp); + srcu_reschedule(ssp, srcu_get_delay(ssp)); +} + +void srcutorture_get_gp_data(enum rcutorture_type test_type, + struct srcu_struct *ssp, int *flags, + unsigned long *gp_seq) +{ + if (test_type != SRCU_FLAVOR) + return; + *flags = 0; + *gp_seq = rcu_seq_current(&ssp->srcu_gp_seq); +} +EXPORT_SYMBOL_GPL(srcutorture_get_gp_data); + +void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf) +{ + int cpu; + int idx; + unsigned long s0 = 0, s1 = 0; + + idx = ssp->srcu_idx & 0x1; + pr_alert("%s%s Tree SRCU g%ld per-CPU(idx=%d):", + tt, tf, rcu_seq_current(&ssp->srcu_gp_seq), idx); + for_each_possible_cpu(cpu) { + unsigned long l0, l1; + unsigned long u0, u1; + long c0, c1; + struct srcu_data *sdp; + + sdp = per_cpu_ptr(ssp->sda, cpu); + u0 = data_race(sdp->srcu_unlock_count[!idx]); + u1 = data_race(sdp->srcu_unlock_count[idx]); + + /* + * Make sure that a lock is always counted if the corresponding + * unlock is counted. + */ + smp_rmb(); + + l0 = data_race(sdp->srcu_lock_count[!idx]); + l1 = data_race(sdp->srcu_lock_count[idx]); + + c0 = l0 - u0; + c1 = l1 - u1; + pr_cont(" %d(%ld,%ld %c)", + cpu, c0, c1, + "C."[rcu_segcblist_empty(&sdp->srcu_cblist)]); + s0 += c0; + s1 += c1; + } + pr_cont(" T(%ld,%ld)\n", s0, s1); +} +EXPORT_SYMBOL_GPL(srcu_torture_stats_print); + +static int __init srcu_bootup_announce(void) +{ + pr_info("Hierarchical SRCU implementation.\n"); + if (exp_holdoff != DEFAULT_SRCU_EXP_HOLDOFF) + pr_info("\tNon-default auto-expedite holdoff of %lu ns.\n", exp_holdoff); + return 0; +} +early_initcall(srcu_bootup_announce); + +void __init srcu_init(void) +{ + struct srcu_struct *ssp; + + srcu_init_done = true; + while (!list_empty(&srcu_boot_list)) { + ssp = list_first_entry(&srcu_boot_list, struct srcu_struct, + work.work.entry); + check_init_srcu_struct(ssp); + list_del_init(&ssp->work.work.entry); + queue_work(rcu_gp_wq, &ssp->work.work); + } +} + +#ifdef CONFIG_MODULES + +/* Initialize any global-scope srcu_struct structures used by this module. */ +static int srcu_module_coming(struct module *mod) +{ + int i; + struct srcu_struct **sspp = mod->srcu_struct_ptrs; + int ret; + + for (i = 0; i < mod->num_srcu_structs; i++) { + ret = init_srcu_struct(*(sspp++)); + if (WARN_ON_ONCE(ret)) + return ret; + } + return 0; +} + +/* Clean up any global-scope srcu_struct structures used by this module. */ +static void srcu_module_going(struct module *mod) +{ + int i; + struct srcu_struct **sspp = mod->srcu_struct_ptrs; + + for (i = 0; i < mod->num_srcu_structs; i++) + cleanup_srcu_struct(*(sspp++)); +} + +/* Handle one module, either coming or going. */ +static int srcu_module_notify(struct notifier_block *self, + unsigned long val, void *data) +{ + struct module *mod = data; + int ret = 0; + + switch (val) { + case MODULE_STATE_COMING: + ret = srcu_module_coming(mod); + break; + case MODULE_STATE_GOING: + srcu_module_going(mod); + break; + default: + break; + } + return ret; +} + +static struct notifier_block srcu_module_nb = { + .notifier_call = srcu_module_notify, + .priority = 0, +}; + +static __init int init_srcu_module_notifier(void) +{ + int ret; + + ret = register_module_notifier(&srcu_module_nb); + if (ret) + pr_warn("Failed to register srcu module notifier\n"); + return ret; +} +late_initcall(init_srcu_module_notifier); + +#endif /* #ifdef CONFIG_MODULES */ |