/* SPDX-License-Identifier: GPL-2.0+ */
/*
* Read-Copy Update mechanism for mutual exclusion (tree-based version)
* Internal non-public definitions that provide either classic
* or preemptible semantics.
*
* Copyright Red Hat, 2009
* Copyright IBM Corporation, 2009
* Copyright SUSE, 2021
*
* Author: Ingo Molnar <[email protected]>
* Paul E. McKenney <[email protected]>
* Frederic Weisbecker <[email protected]>
*/
#ifdef CONFIG_RCU_NOCB_CPU
static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp)
{
/* Race on early boot between thread creation and assignment */
if (!rdp->nocb_cb_kthread || !rdp->nocb_gp_kthread)
return true;
if (current == rdp->nocb_cb_kthread || current == rdp->nocb_gp_kthread)
if (in_task())
return true;
return false;
}
/*
* Offload callback processing from the boot-time-specified set of CPUs
* specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
* created that pull the callbacks from the corresponding CPU, wait for
* a grace period to elapse, and invoke the callbacks. These kthreads
* are organized into GP kthreads, which manage incoming callbacks, wait for
* grace periods, and awaken CB kthreads, and the CB kthreads, which only
* invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
* do a wake_up() on their GP kthread when they insert a callback into any
* empty list, unless the rcu_nocb_poll boot parameter has been specified,
* in which case each kthread actively polls its CPU. (Which isn't so great
* for energy efficiency, but which does reduce RCU's overhead on that CPU.)
*
* This is intended to be used in conjunction with Frederic Weisbecker's
* adaptive-idle work, which would seriously reduce OS jitter on CPUs
* running CPU-bound user-mode computations.
*
* Offloading of callbacks can also be used as an energy-efficiency
* measure because CPUs with no RCU callbacks queued are more aggressive
* about entering dyntick-idle mode.
*/
/*
* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
* If the list is invalid, a warning is emitted and all CPUs are offloaded.
*/
static int __init rcu_nocb_setup(char *str)
{
alloc_bootmem_cpumask_var(&rcu_nocb_mask);
if (*str == '=') {
if (cpulist_parse(++str, rcu_nocb_mask)) {
pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
cpumask_setall(rcu_nocb_mask);
}
}
rcu_state.nocb_is_setup = true;
return 1;
}
__setup("rcu_nocbs", rcu_nocb_setup);
static int __init parse_rcu_nocb_poll(char *arg)
{
rcu_nocb_poll = true;
return 1;
}
__setup("rcu_nocb_poll", parse_rcu_nocb_poll);
/*
* Don't bother bypassing ->cblist if the call_rcu() rate is low.
* After all, the main point of bypassing is to avoid lock contention
* on ->nocb_lock, which only can happen at high call_rcu() rates.
*/
static int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ;
module_param(nocb_nobypass_lim_per_jiffy, int, 0);
/*
* Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the
* lock isn't immediately available, perform minimal sanity check.
*/
static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
__acquires(&rdp->nocb_bypass_lock)
{
lockdep_assert_irqs_disabled();
if (raw_spin_trylock(&rdp->nocb_bypass_lock))
return;
/*
* Contention expected only when local enqueue collide with
* remote flush from kthreads.
*/
WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
raw_spin_lock(&rdp->nocb_bypass_lock);
}
/*
* Conditionally acquire the specified rcu_data structure's
* ->nocb_bypass_lock.
*/
static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp)
{
lockdep_assert_irqs_disabled();
return raw_spin_trylock(&rdp->nocb_bypass_lock);
}
/*
* Release the specified rcu_data structure's ->nocb_bypass_lock.
*/
static void rcu_nocb_bypass_unlock(struct rcu_data *rdp)
__releases(&rdp->nocb_bypass_lock)
{
lockdep_assert_irqs_disabled();
raw_spin_unlock(&rdp->nocb_bypass_lock);
}
/*
* Acquire the specified rcu_data structure's ->nocb_lock, but only
* if it corresponds to a no-CBs CPU.
*/
static void rcu_nocb_lock(struct rcu_data *rdp)
{
lockdep_assert_irqs_disabled();
if (!rcu_rdp_is_offloaded(rdp))
return;
raw_spin_lock(&rdp->nocb_lock);
}
/*
* Release the specified rcu_data structure's ->nocb_lock, but only
* if it corresponds to a no-CBs CPU.
*/
static void rcu_nocb_unlock(struct rcu_data *rdp)
{
if (rcu_rdp_is_offloaded(rdp)) {
lockdep_assert_irqs_disabled();
raw_spin_unlock(&rdp->nocb_lock);
}
}
/*
* Release the specified rcu_data structure's ->nocb_lock and restore
* interrupts, but only if it corresponds to a no-CBs CPU.
*/
static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
unsigned long flags)
{
if (rcu_rdp_is_offloaded(rdp)) {
lockdep_assert_irqs_disabled();
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
} else {
local_irq_restore(flags);
}
}
/* Lockdep check that ->cblist may be safely accessed. */
static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
{
lockdep_assert_irqs_disabled();
if (rcu_rdp_is_offloaded(rdp))
lockdep_assert_held(&rdp->nocb_lock);
}
/*
* Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
* grace period.
*/
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
{
swake_up_all(sq);
}
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
{
return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1];
}
static void rcu_init_one_nocb(struct rcu_node *rnp)
{
init_swait_queue_head(&rnp->nocb_gp_wq[0]);
init_swait_queue_head(&rnp->nocb_gp_wq[1]);
}
static bool __wake_nocb_gp(struct rcu_data *rdp_gp,
struct rcu_data *rdp,
bool force, unsigned long flags)
__releases(rdp_gp->nocb_gp_lock)
{
bool needwake = false;
if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) {
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("AlreadyAwake"));
return false;
}
if (rdp_gp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
WRITE_ONCE(rdp_gp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
del_timer(&rdp_gp->nocb_timer);
}
if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) {
WRITE_ONCE(rdp_gp->nocb_gp_sleep, false);
needwake = true;
}
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
if (needwake) {
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake"));
swake_up_one_online(&rdp_gp->nocb_gp_wq);
}
return needwake;
}
/*
* Kick the GP kthread for this NOCB group.
*/
static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
{
unsigned long flags;
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
return __wake_nocb_gp(rdp_gp, rdp, force, flags);
}
#ifdef CONFIG_RCU_LAZY
/*
* LAZY_FLUSH_JIFFIES decides the maximum amount of time that
* can elapse before lazy callbacks are flushed. Lazy callbacks
* could be flushed much earlier for a number of other reasons
* however, LAZY_FLUSH_JIFFIES will ensure no lazy callbacks are
* left unsubmitted to RCU after those many jiffies.
*/
#define LAZY_FLUSH_JIFFIES (10 * HZ)
static unsigned long jiffies_lazy_flush = LAZY_FLUSH_JIFFIES;
// To be called only from test code.
void rcu_set_jiffies_lazy_flush(unsigned long jif)
{
jiffies_lazy_flush = jif;
}
EXPORT_SYMBOL(rcu_set_jiffies_lazy_flush);
unsigned long rcu_get_jiffies_lazy_flush(void)
{
return jiffies_lazy_flush;
}
EXPORT_SYMBOL(rcu_get_jiffies_lazy_flush);
#endif
/*
* Arrange to wake the GP kthread for this NOCB group at some future
* time when it is safe to do so.
*/
static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
const char *reason)
{
unsigned long flags;
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
/*
* Bypass wakeup overrides previous deferments. In case of
* callback storms, no need to wake up too early.
*/
if (waketype == RCU_NOCB_WAKE_LAZY &&
rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) {
mod_timer(&rdp_gp->nocb_timer, jiffies + rcu_get_jiffies_lazy_flush());
WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
} else if (waketype == RCU_NOCB_WAKE_BYPASS) {
mod_timer(&rdp_gp->nocb_timer, jiffies + 2);
WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
} else {
if (rdp_gp->nocb_defer_wakeup < RCU_NOCB_WAKE)
mod_timer(&rdp_gp->nocb_timer, jiffies + 1);
if (rdp_gp->nocb_defer_wakeup < waketype)
WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
}
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
}
/*
* Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
* However, if there is a callback to be enqueued and if ->nocb_bypass
* proves to be initially empty, just return false because the no-CB GP
* kthread may need to be awakened in this case.
*
* Return true if there was something to be flushed and it succeeded, otherwise
* false.
*
* Note that this function always returns true if rhp is NULL.
*/
static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp_in,
unsigned long j, bool lazy)
{
struct rcu_cblist rcl;
struct rcu_head *rhp = rhp_in;
WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp));
rcu_lockdep_assert_cblist_protected(rdp);
lockdep_assert_held(&rdp->nocb_bypass_lock);
if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) {
raw_spin_unlock(&rdp->nocb_bypass_lock);
return false;
}
/* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
if (rhp)
rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
/*
* If the new CB requested was a lazy one, queue it onto the main
* ->cblist so that we can take advantage of the grace-period that will
* happen regardless. But queue it onto the bypass list first so that
* the lazy CB is ordered with the existing CBs in the bypass list.
*/
if (lazy && rhp) {
rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
rhp = NULL;
}
rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
WRITE_ONCE(rdp->lazy_len, 0);
rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
WRITE_ONCE(rdp->nocb_bypass_first, j);
rcu_nocb_bypass_unlock(rdp);
return true;
}
/*
* Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
* However, if there is a callback to be enqueued and if ->nocb_bypass
* proves to be initially empty, just return false because the no-CB GP
* kthread may need to be awakened in this case.
*
* Note that this function always returns true if rhp is NULL.
*/
static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
unsigned long j, bool lazy)
{
if (!rcu_rdp_is_offloaded(rdp))
return true;
rcu_lockdep_assert_cblist_protected(rdp);
rcu_nocb_bypass_lock(rdp);
return rcu_nocb_do_flush_bypass(rdp, rhp, j, lazy);
}
/*
* If the ->nocb_bypass_lock is immediately available, flush the
* ->nocb_bypass queue into ->cblist.
*/
static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
{
rcu_lockdep_assert_cblist_protected(rdp);
if (!rcu_rdp_is_offloaded(rdp) ||
!rcu_nocb_bypass_trylock(rdp))
return;
WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j, false));
}
/*
* See whether it is appropriate to use the ->nocb_bypass list in order
* to control contention on ->nocb_lock. A limited number of direct
* enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass
* is non-empty, further callbacks must be placed into ->nocb_bypass,
* otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch
* back to direct use of ->cblist. However, ->nocb_bypass should not be
* used if ->cblist is empty, because otherwise callbacks can be stranded
* on ->nocb_bypass because we cannot count on the current CPU ever again
* invoking call_rcu(). The general rule is that if ->nocb_bypass is
* non-empty, the corresponding no-CBs grace-period kthread must not be
* in an indefinite sleep state.
*
* Finally, it is not permitted to use the bypass during early boot,
* as doing so would confuse the auto-initialization code. Besides
* which, there is no point in worrying about lock contention while
* there is only one CPU in operation.
*/
static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
bool *was_alldone, unsigned long flags,
bool lazy)
{
unsigned long c;
unsigned long cur_gp_seq;
unsigned long j = jiffies;
long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
bool bypass_is_lazy = (ncbs == READ_ONCE(rdp->lazy_len));
lockdep_assert_irqs_disabled();
// Pure softirq/rcuc based processing: no bypassing, no
// locking.
if (!rcu_rdp_is_offloaded(rdp)) {
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
return false;
}
// Don't use ->nocb_bypass during early boot.
if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
rcu_nocb_lock(rdp);
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
return false;
}
// If we have advanced to a new jiffy, reset counts to allow
// moving back from ->nocb_bypass to ->cblist.
if (j == rdp->nocb_nobypass_last) {
c = rdp->nocb_nobypass_count + 1;
} else {
WRITE_ONCE(rdp->nocb_nobypass_last, j);
c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy;
if (ULONG_CMP_LT(rdp->nocb_nobypass_count,
nocb_nobypass_lim_per_jiffy))
c = 0;
else if (c > nocb_nobypass_lim_per_jiffy)
c = nocb_nobypass_lim_per_jiffy;
}
WRITE_ONCE(rdp->nocb_nobypass_count, c);
// If there hasn't yet been all that many ->cblist enqueues
// this jiffy, tell the caller to enqueue onto ->cblist. But flush
// ->nocb_bypass first.
// Lazy CBs throttle this back and do immediate bypass queuing.
if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy && !lazy) {
rcu_nocb_lock(rdp);
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
if (*was_alldone)
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("FirstQ"));
WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j, false));
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
return false; // Caller must enqueue the callback.
}
// If ->nocb_bypass has been used too long or is too full,
// flush ->nocb_bypass to ->cblist.
if ((ncbs && !bypass_is_lazy && j != READ_ONCE(rdp->nocb_bypass_first)) ||
(ncbs && bypass_is_lazy &&
(time_after(j, READ_ONCE(rdp->nocb_bypass_first) + rcu_get_jiffies_lazy_flush()))) ||
ncbs >= qhimark) {
rcu_nocb_lock(rdp);
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
if (!rcu_nocb_flush_bypass(rdp, rhp, j, lazy)) {
if (*was_alldone)
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("FirstQ"));
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
return false; // Caller must enqueue the callback.
}
if (j != rdp->nocb_gp_adv_time &&
rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
rcu_advance_cbs_nowake(rdp->mynode, rdp);
rdp->nocb_gp_adv_time = j;
}
// The flush succeeded and we moved CBs into the regular list.
// Don't wait for the wake up timer as it may be too far ahead.
// Wake up the GP thread now instead, if the cblist was empty.
__call_rcu_nocb_wake(rdp, *was_alldone, flags);
return true; // Callback already enqueued.
}
// We need to use the bypass.
rcu_nocb_bypass_lock(rdp);
ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
if (lazy)
WRITE_ONCE(rdp->lazy_len, rdp->lazy_len + 1);
if (!ncbs) {
WRITE_ONCE(rdp->nocb_bypass_first, j);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
}
rcu_nocb_bypass_unlock(rdp);
// A wake up of the grace period kthread or timer adjustment
// needs to be done only if:
// 1. Bypass list was fully empty before (this is the first
// bypass list entry), or:
// 2. Both of these conditions are met:
// a. The bypass list previously had only lazy CBs, and:
// b. The new CB is non-lazy.
if (!ncbs || (bypass_is_lazy && !lazy)) {
// No-CBs GP kthread might be indefinitely asleep, if so, wake.
rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("FirstBQwake"));
__call_rcu_nocb_wake(rdp, true, flags);
} else {
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("FirstBQnoWake"));
rcu_nocb_unlock(rdp);
}
}
return true; // Callback already enqueued.
}
/*
* Awaken the no-CBs grace-period kthread if needed, either due to it
* legitimately being asleep or due to overload conditions.
*
* If warranted, also wake up the kthread servicing this CPUs queues.
*/
static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
unsigned long flags)
__releases(rdp->nocb_lock)
{
long bypass_len;
unsigned long cur_gp_seq;
unsigned long j;
long lazy_len;
long len;
struct task_struct *t;
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
// If we are being polled or there is no kthread, just leave.
t = READ_ONCE(rdp->nocb_gp_kthread);
if (rcu_nocb_poll || !t) {
rcu_nocb_unlock(rdp);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("WakeNotPoll"));
return;
}
// Need to actually to a wakeup.
len = rcu_segcblist_n_cbs(&rdp->cblist);
bypass_len = rcu_cblist_n_cbs(&rdp->nocb_bypass);
lazy_len = READ_ONCE(rdp->lazy_len);
if (was_alldone) {
rdp->qlen_last_fqs_check = len;
// Only lazy CBs in bypass list
if (lazy_len && bypass_len == lazy_len) {
rcu_nocb_unlock(rdp);
wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY,
TPS("WakeLazy"));
} else if (!irqs_disabled_flags(flags)) {
/* ... if queue was empty ... */
rcu_nocb_unlock(rdp);
wake_nocb_gp(rdp, false);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("WakeEmpty"));
} else {
rcu_nocb_unlock(rdp);
wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
TPS("WakeEmptyIsDeferred"));
}
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
/* ... or if many callbacks queued. */
rdp->qlen_last_fqs_check = len;
j = jiffies;
if (j != rdp->nocb_gp_adv_time &&
rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
rcu_advance_cbs_nowake(rdp->mynode, rdp);
rdp->nocb_gp_adv_time = j;
}
smp_mb(); /* Enqueue before timer_pending(). */
if ((rdp->nocb_cb_sleep ||
!rcu_segcblist_ready_cbs(&rdp->cblist)) &&
!timer_pending(&rdp_gp->nocb_timer)) {
rcu_nocb_unlock(rdp);
wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
TPS("WakeOvfIsDeferred"));
} else {
rcu_nocb_unlock(rdp);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
}
} else {
rcu_nocb_unlock(rdp);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
}
}
static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
rcu_callback_t func, unsigned long flags, bool lazy)
{
bool was_alldone;
if (!rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy)) {
/* Not enqueued on bypass but locked, do regular enqueue */
rcutree_enqueue(rdp, head, func);
__call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
}
}
static void nocb_gp_toggle_rdp(struct rcu_data *rdp_gp, struct rcu_data *rdp)
{
struct rcu_segcblist *cblist = &rdp->cblist;
unsigned long flags;
/*
* Locking orders future de-offloaded callbacks enqueue against previous
* handling of this rdp. Ie: Make sure rcuog is done with this rdp before
* deoffloaded callbacks can be enqueued.
*/
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_OFFLOADED)) {
/*
* Offloading. Set our flag and notify the offload worker.
* We will handle this rdp until it ever gets de-offloaded.
*/
list_add_tail(&rdp->nocb_entry_rdp, &rdp_gp->nocb_head_rdp);
rcu_segcblist_set_flags(cblist, SEGCBLIST_OFFLOADED);
} else {
/*
* De-offloading. Clear our flag and notify the de-offload worker.
* We will ignore this rdp until it ever gets re-offloaded.
*/
list_del(&rdp->nocb_entry_rdp);
rcu_segcblist_clear_flags(cblist, SEGCBLIST_OFFLOADED);
}
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
}
static void nocb_gp_sleep(struct rcu_data *my_rdp, int cpu)
{
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
!READ_ONCE(my_rdp->nocb_gp_sleep));
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
}
/*
* No-CBs GP kthreads come here to wait for additional callbacks to show up
* or for grace periods to end.
*/
static void nocb_gp_wait(struct rcu_data *my_rdp)
{
bool bypass = false;
int __maybe_unused cpu = my_rdp->cpu;
unsigned long cur_gp_seq;
unsigned long flags;
bool gotcbs = false;
unsigned long j = jiffies;
bool lazy = false;
bool needwait_gp = false; // This prevents actual uninitialized use.
bool needwake;
bool needwake_gp;
struct rcu_data *rdp, *rdp_toggling = NULL;
struct rcu_node *rnp;
unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
bool wasempty = false;
/*
* Each pass through the following loop checks for CBs and for the
* nearest grace period (if any) to wait for next. The CB kthreads
* and the global grace-period kthread are awakened if needed.
*/
WARN_ON_ONCE(my_rdp->nocb_gp_rdp != my_rdp);
/*
* An rcu_data structure is removed from the list after its
* CPU is de-offloaded and added to the list before that CPU is
* (re-)offloaded. If the following loop happens to be referencing
* that rcu_data structure during the time that the corresponding
* CPU is de-offloaded and then immediately re-offloaded, this
* loop's rdp pointer will be carried to the end of the list by
* the resulting pair of list operations. This can cause the loop
* to skip over some of the rcu_data structures that were supposed
* to have been scanned. Fortunately a new iteration through the
* entire loop is forced after a given CPU's rcu_data structure
* is added to the list, so the skipped-over rcu_data structures
* won't be ignored for long.
*/
list_for_each_entry(rdp, &my_rdp->nocb_head_rdp, nocb_entry_rdp) {
long bypass_ncbs;
bool flush_bypass = false;
long lazy_ncbs;
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
rcu_nocb_lock_irqsave(rdp, flags);
lockdep_assert_held(&rdp->nocb_lock);
bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
lazy_ncbs = READ_ONCE(rdp->lazy_len);
if (bypass_ncbs && (lazy_ncbs == bypass_ncbs) &&
(time_after(j, READ_ONCE(rdp->nocb_bypass_first) + rcu_get_jiffies_lazy_flush()) ||
bypass_ncbs > 2 * qhimark)) {
flush_bypass = true;
} else if (bypass_ncbs && (lazy_ncbs != bypass_ncbs) &&
(time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
bypass_ncbs > 2 * qhimark)) {
flush_bypass = true;
} else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
rcu_nocb_unlock_irqrestore(rdp, flags);
continue; /* No callbacks here, try next. */
}
if (flush_bypass) {
// Bypass full or old, so flush it.
(void)rcu_nocb_try_flush_bypass(rdp, j);
bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
lazy_ncbs = READ_ONCE(rdp->lazy_len);
}
if (bypass_ncbs) {
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
bypass_ncbs == lazy_ncbs ? TPS("Lazy") : TPS("Bypass"));
if (bypass_ncbs == lazy_ncbs)
lazy = true;
else
bypass = true;
}
rnp = rdp->mynode;
// Advance callbacks if helpful and low contention.
needwake_gp = false;
if (!rcu_segcblist_restempty(&rdp->cblist,
RCU_NEXT_READY_TAIL) ||
(rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
needwake_gp = rcu_advance_cbs(rnp, rdp);
wasempty = rcu_segcblist_restempty(&rdp->cblist,
RCU_NEXT_READY_TAIL);
raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
}
// Need to wait on some grace period?
WARN_ON_ONCE(wasempty &&
!rcu_segcblist_restempty(&rdp->cblist,
RCU_NEXT_READY_TAIL));
if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
if (!needwait_gp ||
ULONG_CMP_LT(cur_gp_seq, wait_gp_seq))
wait_gp_seq = cur_gp_seq;
needwait_gp = true;
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("NeedWaitGP"));
}
if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
needwake = rdp->nocb_cb_sleep;
WRITE_ONCE(rdp->nocb_cb_sleep, false);
} else {
needwake = false;
}
rcu_nocb_unlock_irqrestore(rdp, flags);
if (needwake) {
swake_up_one(&rdp->nocb_cb_wq);
gotcbs = true;
}
if (needwake_gp)
rcu_gp_kthread_wake();
}
my_rdp->nocb_gp_bypass = bypass;
my_rdp->nocb_gp_gp = needwait_gp;
my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
// At least one child with non-empty ->nocb_bypass, so set
// timer in order to avoid stranding its callbacks.
if (!rcu_nocb_poll) {
// If bypass list only has lazy CBs. Add a deferred lazy wake up.
if (lazy && !bypass) {
wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_LAZY,
TPS("WakeLazyIsDeferred"));
// Otherwise add a deferred bypass wake up.
} else if (bypass) {
wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS,
TPS("WakeBypassIsDeferred"));
}
}
if (rcu_nocb_poll) {
/* Polling, so trace if first poll in the series. */
if (gotcbs)
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
if (list_empty(&my_rdp->nocb_head_rdp)) {
raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
if (!my_rdp->nocb_toggling_rdp)
WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
/* Wait for any offloading rdp */
nocb_gp_sleep(my_rdp, cpu);
} else {
schedule_timeout_idle(1);
}
} else if (!needwait_gp) {
/* Wait for callbacks to appear. */
nocb_gp_sleep(my_rdp, cpu);
} else {
rnp = my_rdp->mynode;
trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));
swait_event_interruptible_exclusive(
rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1],
rcu_seq_done(&rnp->gp_seq, wait_gp_seq) ||
!READ_ONCE(my_rdp->nocb_gp_sleep));
trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait"));
}
if (!rcu_nocb_poll) {
raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
// (De-)queue an rdp to/from the group if its nocb state is changing
rdp_toggling = my_rdp->nocb_toggling_rdp;
if (rdp_toggling)
my_rdp->nocb_toggling_rdp = NULL;
if (my_rdp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
del_timer(&my_rdp->nocb_timer);
}
WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
} else {
rdp_toggling = READ_ONCE(my_rdp->nocb_toggling_rdp);
if (rdp_toggling) {
/*
* Paranoid locking to make sure nocb_toggling_rdp is well
* reset *before* we (re)set SEGCBLIST_KTHREAD_GP or we could
* race with another round of nocb toggling for this rdp.
* Nocb locking should prevent from that already but we stick
* to paranoia, especially in rare path.
*/
raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
my_rdp->nocb_toggling_rdp = NULL;
raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
}
}
if (rdp_toggling) {
nocb_gp_toggle_rdp(my_rdp, rdp_toggling);
swake_up_one(&rdp_toggling->nocb_state_wq);
}
my_rdp->nocb_gp_seq = -1;
WARN_ON(signal_pending(current));
}
/*
* No-CBs grace-period-wait kthread. There is one of these per group
* of CPUs, but only once at least one CPU in that group has come online
* at least once since boot. This kthread checks for newly posted
* callbacks from any of the CPUs it is responsible for, waits for a
* grace period, then awakens all of the rcu_nocb_cb_kthread() instances
* that then have callback-invocation work to do.
*/
static int rcu_nocb_gp_kthread(void *arg)
{
struct rcu_data *rdp = arg;
for (;;) {
WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
nocb_gp_wait(rdp);
cond_resched_tasks_rcu_qs();
}
return 0;
}
static inline bool nocb_cb_wait_cond(struct rcu_data *rdp)
{
return !READ_ONCE(rdp->nocb_cb_sleep) || kthread_should_park();
}
/*
* Invoke any ready callbacks from the corresponding no-CBs CPU,
* then, if there are no more, wait for more to appear.
*/
static void nocb_cb_wait(struct rcu_data *rdp)
{
struct rcu_segcblist *cblist = &rdp->cblist;
unsigned long cur_gp_seq;
unsigned long flags;
bool needwake_gp = false;
struct rcu_node *rnp = rdp->mynode;
swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
nocb_cb_wait_cond(rdp));
if (kthread_should_park()) {
kthread_parkme();
} else if (READ_ONCE(rdp->nocb_cb_sleep)) {
WARN_ON(signal_pending(current));
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
}
WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp));
local_irq_save(flags);
rcu_momentary_eqs();
local_irq_restore(flags);
/*
* Disable BH to provide the expected environment. Also, when
* transitioning to/from NOCB mode, a self-requeuing callback might
* be invoked from softirq. A short grace period could cause both
* instances of this callback would execute concurrently.
*/
local_bh_disable();
rcu_do_batch(rdp);
local_bh_enable();
lockdep_assert_irqs_enabled();
rcu_nocb_lock_irqsave(rdp, flags);
if (rcu_segcblist_nextgp(cblist, &cur_gp_seq) &&
rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
}
if (!rcu_segcblist_ready_cbs(cblist)) {
WRITE_ONCE(rdp->nocb_cb_sleep, true);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
} else {
WRITE_ONCE(rdp->nocb_cb_sleep, false);
}
rcu_nocb_unlock_irqrestore(rdp, flags);
if (needwake_gp)
rcu_gp_kthread_wake();
}
/*
* Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
* nocb_cb_wait() to do the dirty work.
*/
static int rcu_nocb_cb_kthread(void *arg)
{
struct rcu_data *rdp = arg;
// Each pass through this loop does one callback batch, and,
// if there are no more ready callbacks, waits for them.
for (;;) {
nocb_cb_wait(rdp);
cond_resched_tasks_rcu_qs();
}
return 0;
}
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
{
return READ_ONCE(rdp->nocb_defer_wakeup) >= level;
}
/* Do a deferred wakeup of rcu_nocb_kthread(). */
static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp_gp,
struct rcu_data *rdp, int level,
unsigned long flags)
__releases(rdp_gp->nocb_gp_lock)
{
int ndw;
int ret;
if (!rcu_nocb_need_deferred_wakeup(rdp_gp, level)) {
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
return false;
}
ndw = rdp_gp->nocb_defer_wakeup;
ret = __wake_nocb_gp(rdp_gp, rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake"));
return ret;
}
/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
{
unsigned long flags;
struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
WARN_ON_ONCE(rdp->nocb_gp_rdp != rdp);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer"));
raw_spin_lock_irqsave(&rdp->nocb_gp_lock, flags);
smp_mb__after_spinlock(); /* Timer expire before wakeup. */
do_nocb_deferred_wakeup_common(rdp, rdp, RCU_NOCB_WAKE_BYPASS, flags);
}
/*
* Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
* This means we do an inexact common-case check. Note that if
* we miss, ->nocb_timer will eventually clean things up.
*/
static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
{
unsigned long flags;
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
if (!rdp_gp || !rcu_nocb_need_deferred_wakeup(rdp_gp, RCU_NOCB_WAKE))
return false;
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
return do_nocb_deferred_wakeup_common(rdp_gp, rdp, RCU_NOCB_WAKE, flags);
}
void rcu_nocb_flush_deferred_wakeup(void)
{
do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data));
}
EXPORT_SYMBOL_GPL(rcu_nocb_flush_deferred_wakeup);
static int rcu_nocb_queue_toggle_rdp(struct rcu_data *rdp)
{
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
bool wake_gp = false;
unsigned long flags;
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
// Queue this rdp for add/del to/from the list to iterate on rcuog
WRITE_ONCE(rdp_gp->nocb_toggling_rdp, rdp);
if (rdp_gp->nocb_gp_sleep) {
rdp_gp->nocb_gp_sleep = false;
wake_gp = true;
}
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
return wake_gp;
}
static bool rcu_nocb_rdp_deoffload_wait_cond(struct rcu_data *rdp)
{
unsigned long flags;
bool ret;
/*
* Locking makes sure rcuog is done handling this rdp before deoffloaded
* enqueue can happen. Also it keeps the SEGCBLIST_OFFLOADED flag stable
* while the ->nocb_lock is held.
*/
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
ret = !rcu_segcblist_test_flags(&rdp->cblist, SEGCBLIST_OFFLOADED);
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
return ret;
}
static int rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
{
unsigned long flags;
int wake_gp;
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
/* CPU must be offline, unless it's early boot */
WARN_ON_ONCE(cpu_online(rdp->cpu) && rdp->cpu != raw_smp_processor_id());
pr_info("De-offloading %d\n", rdp->cpu);
/* Flush all callbacks from segcblist and bypass */
rcu_barrier();
/*
* Make sure the rcuoc kthread isn't in the middle of a nocb locked
* sequence while offloading is deactivated, along with nocb locking.
*/
if (rdp->nocb_cb_kthread)
kthread_park(rdp->nocb_cb_kthread);
rcu_nocb_lock_irqsave(rdp, flags);
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist));
rcu_nocb_unlock_irqrestore(rdp, flags);
wake_gp = rcu_nocb_queue_toggle_rdp(rdp);
mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
if (rdp_gp->nocb_gp_kthread) {
if (wake_gp)
wake_up_process(rdp_gp->nocb_gp_kthread);
swait_event_exclusive(rdp->nocb_state_wq,
rcu_nocb_rdp_deoffload_wait_cond(rdp));
} else {
/*
* No kthread to clear the flags for us or remove the rdp from the nocb list
* to iterate. Do it here instead. Locking doesn't look stricly necessary
* but we stick to paranoia in this rare path.
*/
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_OFFLOADED);
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
list_del(&rdp->nocb_entry_rdp);
}
mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);
return 0;
}
int rcu_nocb_cpu_deoffload(int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
int ret = 0;
cpus_read_lock();
mutex_lock(&rcu_state.nocb_mutex);
if (rcu_rdp_is_offloaded(rdp)) {
if (!cpu_online(cpu)) {
ret = rcu_nocb_rdp_deoffload(rdp);
if (!ret)
cpumask_clear_cpu(cpu, rcu_nocb_mask);
} else {
pr_info("NOCB: Cannot CB-deoffload online CPU %d\n", rdp->cpu);
ret = -EINVAL;
}
}
mutex_unlock(&rcu_state.nocb_mutex);
cpus_read_unlock();
return ret;
}
EXPORT_SYMBOL_GPL(rcu_nocb_cpu_deoffload);
static bool rcu_nocb_rdp_offload_wait_cond(struct rcu_data *rdp)
{
unsigned long flags;
bool ret;
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
ret = rcu_segcblist_test_flags(&rdp->cblist, SEGCBLIST_OFFLOADED);
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
return ret;
}
static int rcu_nocb_rdp_offload(struct rcu_data *rdp)
{
int wake_gp;
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
WARN_ON_ONCE(cpu_online(rdp->cpu));
/*
* For now we only support re-offload, ie: the rdp must have been
* offloaded on boot first.
*/
if (!rdp->nocb_gp_rdp)
return -EINVAL;
if (WARN_ON_ONCE(!rdp_gp->nocb_gp_kthread))
return -EINVAL;
pr_info("Offloading %d\n", rdp->cpu);
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist));
wake_gp = rcu_nocb_queue_toggle_rdp(rdp);
if (wake_gp)
wake_up_process(rdp_gp->nocb_gp_kthread);
swait_event_exclusive(rdp->nocb_state_wq,
rcu_nocb_rdp_offload_wait_cond(rdp));
kthread_unpark(rdp->nocb_cb_kthread);
return 0;
}
int rcu_nocb_cpu_offload(int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
int ret = 0;
cpus_read_lock();
mutex_lock(&rcu_state.nocb_mutex);
if (!rcu_rdp_is_offloaded(rdp)) {
if (!cpu_online(cpu)) {
ret = rcu_nocb_rdp_offload(rdp);
if (!ret)
cpumask_set_cpu(cpu, rcu_nocb_mask);
} else {
pr_info("NOCB: Cannot CB-offload online CPU %d\n", rdp->cpu);
ret = -EINVAL;
}
}
mutex_unlock(&rcu_state.nocb_mutex);
cpus_read_unlock();
return ret;
}
EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
#ifdef CONFIG_RCU_LAZY
static unsigned long
lazy_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
{
int cpu;
unsigned long count = 0;
if (WARN_ON_ONCE(!cpumask_available(rcu_nocb_mask)))
return 0;
/* Protect rcu_nocb_mask against concurrent (de-)offloading. */
if (!mutex_trylock(&rcu_state.nocb_mutex))
return 0;
/* Snapshot count of all CPUs */
for_each_cpu(cpu, rcu_nocb_mask) {
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
count += READ_ONCE(rdp->lazy_len);
}
mutex_unlock(&rcu_state.nocb_mutex);
return count ? count : SHRINK_EMPTY;
}
static unsigned long
lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
{
int cpu;
unsigned long flags;
unsigned long count = 0;
if (WARN_ON_ONCE(!cpumask_available(rcu_nocb_mask)))
return 0;
/*
* Protect against concurrent (de-)offloading. Otherwise nocb locking
* may be ignored or imbalanced.
*/
if (!mutex_trylock(&rcu_state.nocb_mutex)) {
/*
* But really don't insist if nocb_mutex is contended since we
* can't guarantee that it will never engage in a dependency
* chain involving memory allocation. The lock is seldom contended
* anyway.
*/
return 0;
}
/* Snapshot count of all CPUs */
for_each_cpu(cpu, rcu_nocb_mask) {
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
int _count;
if (WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp)))
continue;
if (!READ_ONCE(rdp->lazy_len))
continue;
rcu_nocb_lock_irqsave(rdp, flags);
/*
* Recheck under the nocb lock. Since we are not holding the bypass
* lock we may still race with increments from the enqueuer but still
* we know for sure if there is at least one lazy callback.
*/
_count = READ_ONCE(rdp->lazy_len);
if (!_count) {
rcu_nocb_unlock_irqrestore(rdp, flags);
continue;
}
rcu_nocb_try_flush_bypass(rdp, jiffies);
rcu_nocb_unlock_irqrestore(rdp, flags);
wake_nocb_gp(rdp, false);
sc->nr_to_scan -= _count;
count += _count;
if (sc->nr_to_scan <= 0)
break;
}
mutex_unlock(&rcu_state.nocb_mutex);
return count ? count : SHRINK_STOP;
}
#endif // #ifdef CONFIG_RCU_LAZY
void __init rcu_init_nohz(void)
{
int cpu;
struct rcu_data *rdp;
const struct cpumask *cpumask = NULL;
struct shrinker * __maybe_unused lazy_rcu_shrinker;
#if defined(CONFIG_NO_HZ_FULL)
if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
cpumask = tick_nohz_full_mask;
#endif
if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) &&
!rcu_state.nocb_is_setup && !cpumask)
cpumask = cpu_possible_mask;
if (cpumask) {
if (!cpumask_available(rcu_nocb_mask)) {
if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
return;
}
}
cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);
rcu_state.nocb_is_setup = true;
}
if (!rcu_state.nocb_is_setup)
return;
#ifdef CONFIG_RCU_LAZY
lazy_rcu_shrinker = shrinker_alloc(0, "rcu-lazy");
if (!lazy_rcu_shrinker) {
pr_err("Failed to allocate lazy_rcu shrinker!\n");
} else {
lazy_rcu_shrinker->count_objects = lazy_rcu_shrink_count;
lazy_rcu_shrinker->scan_objects = lazy_rcu_shrink_scan;
shrinker_register(lazy_rcu_shrinker);
}
#endif // #ifdef CONFIG_RCU_LAZY
if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
cpumask_and(rcu_nocb_mask, cpu_possible_mask,
rcu_nocb_mask);
}
if (cpumask_empty(rcu_nocb_mask))
pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
else
pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
cpumask_pr_args(rcu_nocb_mask));
if (rcu_nocb_poll)
pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
for_each_cpu(cpu, rcu_nocb_mask) {
rdp = per_cpu_ptr(&rcu_data, cpu);
if (rcu_segcblist_empty(&rdp->cblist))
rcu_segcblist_init(&rdp->cblist);
rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_OFFLOADED);
}
rcu_organize_nocb_kthreads();
}
/* Initialize per-rcu_data variables for no-CBs CPUs. */
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
init_swait_queue_head(&rdp->nocb_cb_wq);
init_swait_queue_head(&rdp->nocb_gp_wq);
init_swait_queue_head(&rdp->nocb_state_wq);
raw_spin_lock_init(&rdp->nocb_lock);
raw_spin_lock_init(&rdp->nocb_bypass_lock);
raw_spin_lock_init(&rdp->nocb_gp_lock);
timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
rcu_cblist_init(&rdp->nocb_bypass);
WRITE_ONCE(rdp->lazy_len, 0);
mutex_init(&rdp->nocb_gp_kthread_mutex);
}
/*
* If the specified CPU is a no-CBs CPU that does not already have its
* rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
* for this CPU's group has not yet been created, spawn it as well.
*/
static void rcu_spawn_cpu_nocb_kthread(int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
struct rcu_data *rdp_gp;
struct task_struct *t;
struct sched_param sp;
if (!rcu_scheduler_fully_active || !rcu_state.nocb_is_setup)
return;
/* If there already is an rcuo kthread, then nothing to do. */
if (rdp->nocb_cb_kthread)
return;
/* If we didn't spawn the GP kthread first, reorganize! */
sp.sched_priority = kthread_prio;
rdp_gp = rdp->nocb_gp_rdp;
mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
if (!rdp_gp->nocb_gp_kthread) {
t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
"rcuog/%d", rdp_gp->cpu);
if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) {
mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);
goto err;
}
WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
if (kthread_prio)
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
}
mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);
/* Spawn the kthread for this CPU. */
t = kthread_create(rcu_nocb_cb_kthread, rdp,
"rcuo%c/%d", rcu_state.abbr, cpu);
if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
goto err;
if (rcu_rdp_is_offloaded(rdp))
wake_up_process(t);
else
kthread_park(t);
if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_CB_BOOST) && kthread_prio)
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
WRITE_ONCE(rdp->nocb_cb_kthread, t);
WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
return;
err:
/*
* No need to protect against concurrent rcu_barrier()
* because the number of callbacks should be 0 for a non-boot CPU,
* therefore rcu_barrier() shouldn't even try to grab the nocb_lock.
* But hold nocb_mutex to avoid nocb_lock imbalance from shrinker.
*/
WARN_ON_ONCE(system_state > SYSTEM_BOOTING && rcu_segcblist_n_cbs(&rdp->cblist));
mutex_lock(&rcu_state.nocb_mutex);
if (rcu_rdp_is_offloaded(rdp)) {
rcu_nocb_rdp_deoffload(rdp);
cpumask_clear_cpu(cpu, rcu_nocb_mask);
}
mutex_unlock(&rcu_state.nocb_mutex);
}
/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
static int rcu_nocb_gp_stride = -1;
module_param(rcu_nocb_gp_stride, int, 0444);
/*
* Initialize GP-CB relationships for all no-CBs CPU.
*/
static void __init rcu_organize_nocb_kthreads(void)
{
int cpu;
bool firsttime = true;
bool gotnocbs = false;
bool gotnocbscbs = true;
int ls = rcu_nocb_gp_stride;
int nl = 0; /* Next GP kthread. */
struct rcu_data *rdp;
struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */
if (!cpumask_available(rcu_nocb_mask))
return;
if (ls == -1) {
ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
rcu_nocb_gp_stride = ls;
}
/*
* Each pass through this loop sets up one rcu_data structure.
* Should the corresponding CPU come online in the future, then
* we will spawn the needed set of rcu_nocb_kthread() kthreads.
*/
for_each_possible_cpu(cpu) {
rdp = per_cpu_ptr(&rcu_data, cpu);
if (rdp->cpu >= nl) {
/* New GP kthread, set up for CBs & next GP. */
gotnocbs = true;
nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
rdp_gp = rdp;
INIT_LIST_HEAD(&rdp->nocb_head_rdp);
if (dump_tree) {
if (!firsttime)
pr_cont("%s\n", gotnocbscbs
? "" : " (self only)");
gotnocbscbs = false;
firsttime = false;
pr_alert("%s: No-CB GP kthread CPU %d:",
__func__, cpu);
}
} else {
/* Another CB kthread, link to previous GP kthread. */
gotnocbscbs = true;
if (dump_tree)
pr_cont(" %d", cpu);
}
rdp->nocb_gp_rdp = rdp_gp;
if (cpumask_test_cpu(cpu, rcu_nocb_mask))
list_add_tail(&rdp->nocb_entry_rdp, &rdp_gp->nocb_head_rdp);
}
if (gotnocbs && dump_tree)
pr_cont("%s\n", gotnocbscbs ? "" : " (self only)");
}
/*
* Bind the current task to the offloaded CPUs. If there are no offloaded
* CPUs, leave the task unbound. Splat if the bind attempt fails.
*/
void rcu_bind_current_to_nocb(void)
{
if (cpumask_available(rcu_nocb_mask) && !cpumask_empty(rcu_nocb_mask))
WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
}
EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
// The ->on_cpu field is available only in CONFIG_SMP=y, so...
#ifdef CONFIG_SMP
static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
{
return tsp && task_is_running(tsp) && !tsp->on_cpu ? "!" : "";
}
#else // #ifdef CONFIG_SMP
static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
{
return "";
}
#endif // #else #ifdef CONFIG_SMP
/*
* Dump out nocb grace-period kthread state for the specified rcu_data
* structure.
*/
static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
{
struct rcu_node *rnp = rdp->mynode;
pr_info("nocb GP %d %c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu %c CPU %d%s\n",
rdp->cpu,
"kK"[!!rdp->nocb_gp_kthread],
"lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
"dD"[!!rdp->nocb_defer_wakeup],
"tT"[timer_pending(&rdp->nocb_timer)],
"sS"[!!rdp->nocb_gp_sleep],
".W"[swait_active(&rdp->nocb_gp_wq)],
".W"[swait_active(&rnp->nocb_gp_wq[0])],
".W"[swait_active(&rnp->nocb_gp_wq[1])],
".B"[!!rdp->nocb_gp_bypass],
".G"[!!rdp->nocb_gp_gp],
(long)rdp->nocb_gp_seq,
rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops),
rdp->nocb_gp_kthread ? task_state_to_char(rdp->nocb_gp_kthread) : '.',
rdp->nocb_gp_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
show_rcu_should_be_on_cpu(rdp->nocb_gp_kthread));
}
/* Dump out nocb kthread state for the specified rcu_data structure. */
static void show_rcu_nocb_state(struct rcu_data *rdp)
{
char bufw[20];
char bufr[20];
struct rcu_data *nocb_next_rdp;
struct rcu_segcblist *rsclp = &rdp->cblist;
bool waslocked;
bool wassleep;
if (rdp->nocb_gp_rdp == rdp)
show_rcu_nocb_gp_state(rdp);
nocb_next_rdp = list_next_or_null_rcu(&rdp->nocb_gp_rdp->nocb_head_rdp,
&rdp->nocb_entry_rdp,
typeof(*rdp),
nocb_entry_rdp);
sprintf(bufw, "%ld", rsclp->gp_seq[RCU_WAIT_TAIL]);
sprintf(bufr, "%ld", rsclp->gp_seq[RCU_NEXT_READY_TAIL]);
pr_info(" CB %d^%d->%d %c%c%c%c%c F%ld L%ld C%d %c%c%s%c%s%c%c q%ld %c CPU %d%s\n",
rdp->cpu, rdp->nocb_gp_rdp->cpu,
nocb_next_rdp ? nocb_next_rdp->cpu : -1,
"kK"[!!rdp->nocb_cb_kthread],
"bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
"lL"[raw_spin_is_locked(&rdp->nocb_lock)],
"sS"[!!rdp->nocb_cb_sleep],
".W"[swait_active(&rdp->nocb_cb_wq)],
jiffies - rdp->nocb_bypass_first,
jiffies - rdp->nocb_nobypass_last,
rdp->nocb_nobypass_count,
".D"[rcu_segcblist_ready_cbs(rsclp)],
".W"[!rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL)],
rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL) ? "" : bufw,
".R"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL)],
rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL) ? "" : bufr,
".N"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_TAIL)],
".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
rcu_segcblist_n_cbs(&rdp->cblist),
rdp->nocb_cb_kthread ? task_state_to_char(rdp->nocb_cb_kthread) : '.',
rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_cb_kthread) : -1,
show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread));
/* It is OK for GP kthreads to have GP state. */
if (rdp->nocb_gp_rdp == rdp)
return;
waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
wassleep = swait_active(&rdp->nocb_gp_wq);
if (!rdp->nocb_gp_sleep && !waslocked && !wassleep)
return; /* Nothing untoward. */
pr_info(" nocb GP activity on CB-only CPU!!! %c%c%c %c\n",
"lL"[waslocked],
"dD"[!!rdp->nocb_defer_wakeup],
"sS"[!!rdp->nocb_gp_sleep],
".W"[wassleep]);
}
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
/* No ->nocb_lock to acquire. */
static void rcu_nocb_lock(struct rcu_data *rdp)
{
}
/* No ->nocb_lock to release. */
static void rcu_nocb_unlock(struct rcu_data *rdp)
{
}
/* No ->nocb_lock to release. */
static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
unsigned long flags)
{
local_irq_restore(flags);
}
/* Lockdep check that ->cblist may be safely accessed. */
static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
{
lockdep_assert_irqs_disabled();
}
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
{
}
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
{
return NULL;
}
static void rcu_init_one_nocb(struct rcu_node *rnp)
{
}
static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
{
return false;
}
static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
unsigned long j, bool lazy)
{
return true;
}
static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
rcu_callback_t func, unsigned long flags, bool lazy)
{
WARN_ON_ONCE(1); /* Should be dead code! */
}
static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
unsigned long flags)
{
WARN_ON_ONCE(1); /* Should be dead code! */
}
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
}
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
{
return false;
}
static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
{
return false;
}
static void rcu_spawn_cpu_nocb_kthread(int cpu)
{
}
static void show_rcu_nocb_state(struct rcu_data *rdp)
{
}
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
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