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linux-next/kernel/rcu/srcutree.c
Paul E. McKenney 0d2460ba61 Merge branches 'doc.2021.01.06a', 'fixes.2021.01.04b', 'kfree_rcu.2021.01.04a', 'mmdumpobj.2021.01.22a', 'nocb.2021.01.06a', 'rt.2021.01.04a', 'stall.2021.01.06a', 'torture.2021.01.12a' and 'tortureall.2021.01.06a' into HEAD
doc.2021.01.06a: Documentation updates.
fixes.2021.01.04b: Miscellaneous fixes.
kfree_rcu.2021.01.04a: kfree_rcu() updates.
mmdumpobj.2021.01.22a: Dump allocation point for memory blocks.
nocb.2021.01.06a: RCU callback offload updates and cblist segment lengths.
rt.2021.01.04a: Real-time updates.
stall.2021.01.06a: RCU CPU stall warning updates.
torture.2021.01.12a: Torture-test updates and polling SRCU grace-period API.
tortureall.2021.01.06a: Torture-test script updates.
2021-01-22 15:26:44 -08:00

1469 lines
48 KiB
C

// 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);
if (!ssp->sda)
return -ENOMEM;
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 0;
}
#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(lockdep_is_held(ssp) ||
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.
*
* Because cookies are finite in size, wrapping/overflow is possible.
* This is more pronounced on 32-bit systems where cookies are 32 bits,
* where in theory wrapping could happen in about 14 hours assuming
* 25-microsecond expedited SRCU grace periods. However, a more likely
* overflow lower bound is on the order of 24 days in the case of
* one-millisecond SRCU grace periods. Of course, wrapping in a 64-bit
* system requires geologic timespans, as in more than seven million years
* even for expedited SRCU grace periods.
*
* Wrapping/overflow is much more of an issue for CONFIG_SMP=n systems
* that also have CONFIG_PREEMPTION=n, which selects Tiny SRCU. This uses
* a 16-bit cookie, which rcutorture routinely wraps in a matter of a
* few minutes. If this proves to be a problem, this counter will be
* expanded to the same size as for Tree SRCU.
*/
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)
{
long len;
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);
len = ready_cbs.len;
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();
}
WARN_ON_ONCE(ready_cbs.len);
/*
* Update counts, accelerate new callbacks, and if needed,
* schedule another round of callback invocation.
*/
spin_lock_irq_rcu_node(sdp);
rcu_segcblist_add_len(&sdp->srcu_cblist, -len);
(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 */