| // 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; |
| |
| /* 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 amoritized 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; |
| |
| /* If the local srcu_data structure has callbacks, not idle. */ |
| local_irq_save(flags); |
| sdp = this_cpu_ptr(ssp->sda); |
| if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) { |
| local_irq_restore(flags); |
| return false; /* Callbacks already present, so not idle. */ |
| } |
| local_irq_restore(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) |
| { |
| } |
| |
| /* |
| * 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) |
| { |
| unsigned long flags; |
| int idx; |
| bool needexp = false; |
| bool needgp = false; |
| unsigned long s; |
| struct srcu_data *sdp; |
| |
| check_init_srcu_struct(ssp); |
| 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; |
| idx = srcu_read_lock(ssp); |
| local_irq_save(flags); |
| sdp = this_cpu_ptr(ssp->sda); |
| spin_lock_rcu_node(sdp); |
| 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); |
| } |
| |
| /** |
| * 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); |
| |
| /* |
| * 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 = sdp->srcu_unlock_count[!idx]; |
| u1 = sdp->srcu_unlock_count[idx]; |
| |
| /* |
| * Make sure that a lock is always counted if the corresponding |
| * unlock is counted. |
| */ |
| smp_rmb(); |
| |
| l0 = sdp->srcu_lock_count[!idx]; |
| l1 = 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 */ |