/* SPDX-License-Identifier: GPL-2.0+ */
/*
* RCU expedited grace periods
*
* Copyright IBM Corporation, 2016
*
* Authors: Paul E. McKenney <[email protected]>
*/
#include <linux/console.h>
#include <linux/lockdep.h>
static void rcu_exp_handler(void *unused);
static int rcu_print_task_exp_stall(struct rcu_node *rnp);
static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp);
/*
* Record the start of an expedited grace period.
*/
static void rcu_exp_gp_seq_start(void)
{
rcu_seq_start(&rcu_state.expedited_sequence);
rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
}
/*
* Return the value that the expedited-grace-period counter will have
* at the end of the current grace period.
*/
static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void)
{
return rcu_seq_endval(&rcu_state.expedited_sequence);
}
/*
* Record the end of an expedited grace period.
*/
static void rcu_exp_gp_seq_end(void)
{
rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
rcu_seq_end(&rcu_state.expedited_sequence);
smp_mb(); /* Ensure that consecutive grace periods serialize. */
}
/*
* Take a snapshot of the expedited-grace-period counter, which is the
* earliest value that will indicate that a full grace period has
* elapsed since the current time.
*/
static unsigned long rcu_exp_gp_seq_snap(void)
{
unsigned long s;
smp_mb(); /* Caller's modifications seen first by other CPUs. */
s = rcu_seq_snap(&rcu_state.expedited_sequence);
trace_rcu_exp_grace_period(rcu_state.name, s, TPS("snap"));
return s;
}
/*
* Given a counter snapshot from rcu_exp_gp_seq_snap(), return true
* if a full expedited grace period has elapsed since that snapshot
* was taken.
*/
static bool rcu_exp_gp_seq_done(unsigned long s)
{
return rcu_seq_done(&rcu_state.expedited_sequence, s);
}
/*
* Reset the ->expmaskinit values in the rcu_node tree to reflect any
* recent CPU-online activity. Note that these masks are not cleared
* when CPUs go offline, so they reflect the union of all CPUs that have
* ever been online. This means that this function normally takes its
* no-work-to-do fastpath.
*/
static void sync_exp_reset_tree_hotplug(void)
{
bool done;
unsigned long flags;
unsigned long mask;
unsigned long oldmask;
int ncpus = smp_load_acquire(&rcu_state.ncpus); /* Order vs. locking. */
struct rcu_node *rnp;
struct rcu_node *rnp_up;
/* If no new CPUs onlined since last time, nothing to do. */
if (likely(ncpus == rcu_state.ncpus_snap))
return;
rcu_state.ncpus_snap = ncpus;
/*
* Each pass through the following loop propagates newly onlined
* CPUs for the current rcu_node structure up the rcu_node tree.
*/
rcu_for_each_leaf_node(rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rnp->expmaskinit == rnp->expmaskinitnext) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
continue; /* No new CPUs, nothing to do. */
}
/* Update this node's mask, track old value for propagation. */
oldmask = rnp->expmaskinit;
rnp->expmaskinit = rnp->expmaskinitnext;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
/* If was already nonzero, nothing to propagate. */
if (oldmask)
continue;
/* Propagate the new CPU up the tree. */
mask = rnp->grpmask;
rnp_up = rnp->parent;
done = false;
while (rnp_up) {
raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
if (rnp_up->expmaskinit)
done = true;
rnp_up->expmaskinit |= mask;
raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
if (done)
break;
mask = rnp_up->grpmask;
rnp_up = rnp_up->parent;
}
}
}
/*
* Reset the ->expmask values in the rcu_node tree in preparation for
* a new expedited grace period.
*/
static void __maybe_unused sync_exp_reset_tree(void)
{
unsigned long flags;
struct rcu_node *rnp;
sync_exp_reset_tree_hotplug();
rcu_for_each_node_breadth_first(rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
WARN_ON_ONCE(rnp->expmask);
WRITE_ONCE(rnp->expmask, rnp->expmaskinit);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
}
/*
* Return non-zero if there is no RCU expedited grace period in progress
* for the specified rcu_node structure, in other words, if all CPUs and
* tasks covered by the specified rcu_node structure have done their bit
* for the current expedited grace period.
*/
static bool sync_rcu_exp_done(struct rcu_node *rnp)
{
raw_lockdep_assert_held_rcu_node(rnp);
return READ_ONCE(rnp->exp_tasks) == NULL &&
READ_ONCE(rnp->expmask) == 0;
}
/*
* Like sync_rcu_exp_done(), but where the caller does not hold the
* rcu_node's ->lock.
*/
static bool sync_rcu_exp_done_unlocked(struct rcu_node *rnp)
{
unsigned long flags;
bool ret;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
ret = sync_rcu_exp_done(rnp);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return ret;
}
/*
* Report the exit from RCU read-side critical section for the last task
* that queued itself during or before the current expedited preemptible-RCU
* grace period. This event is reported either to the rcu_node structure on
* which the task was queued or to one of that rcu_node structure's ancestors,
* recursively up the tree. (Calm down, calm down, we do the recursion
* iteratively!)
*/
static void __rcu_report_exp_rnp(struct rcu_node *rnp,
bool wake, unsigned long flags)
__releases(rnp->lock)
{
unsigned long mask;
raw_lockdep_assert_held_rcu_node(rnp);
for (;;) {
if (!sync_rcu_exp_done(rnp)) {
if (!rnp->expmask)
rcu_initiate_boost(rnp, flags);
else
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
break;
}
if (rnp->parent == NULL) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
if (wake)
swake_up_one_online(&rcu_state.expedited_wq);
break;
}
mask = rnp->grpmask;
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
rnp = rnp->parent;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
WARN_ON_ONCE(!(rnp->expmask & mask));
WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
}
}
/*
* Report expedited quiescent state for specified node. This is a
* lock-acquisition wrapper function for __rcu_report_exp_rnp().
*/
static void __maybe_unused rcu_report_exp_rnp(struct rcu_node *rnp, bool wake)
{
unsigned long flags;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
__rcu_report_exp_rnp(rnp, wake, flags);
}
/*
* Report expedited quiescent state for multiple CPUs, all covered by the
* specified leaf rcu_node structure.
*/
static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
unsigned long mask, bool wake)
{
int cpu;
unsigned long flags;
struct rcu_data *rdp;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (!(rnp->expmask & mask)) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
rdp = per_cpu_ptr(&rcu_data, cpu);
if (!IS_ENABLED(CONFIG_NO_HZ_FULL) || !rdp->rcu_forced_tick_exp)
continue;
rdp->rcu_forced_tick_exp = false;
tick_dep_clear_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
}
__rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */
}
/*
* Report expedited quiescent state for specified rcu_data (CPU).
*/
static void rcu_report_exp_rdp(struct rcu_data *rdp)
{
WRITE_ONCE(rdp->cpu_no_qs.b.exp, false);
rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true);
}
/* Common code for work-done checking. */
static bool sync_exp_work_done(unsigned long s)
{
if (rcu_exp_gp_seq_done(s)) {
trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done"));
/*
* Order GP completion with preceding accesses. Order also GP
* completion with post GP update side accesses. Pairs with
* rcu_seq_end().
*/
smp_mb();
return true;
}
return false;
}
/*
* Funnel-lock acquisition for expedited grace periods. Returns true
* if some other task completed an expedited grace period that this task
* can piggy-back on, and with no mutex held. Otherwise, returns false
* with the mutex held, indicating that the caller must actually do the
* expedited grace period.
*/
static bool exp_funnel_lock(unsigned long s)
{
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
struct rcu_node *rnp = rdp->mynode;
struct rcu_node *rnp_root = rcu_get_root();
/* Low-contention fastpath. */
if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
(rnp == rnp_root ||
ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
mutex_trylock(&rcu_state.exp_mutex))
goto fastpath;
/*
* Each pass through the following loop works its way up
* the rcu_node tree, returning if others have done the work or
* otherwise falls through to acquire ->exp_mutex. The mapping
* from CPU to rcu_node structure can be inexact, as it is just
* promoting locality and is not strictly needed for correctness.
*/
for (; rnp != NULL; rnp = rnp->parent) {
if (sync_exp_work_done(s))
return true;
/* Work not done, either wait here or go up. */
spin_lock(&rnp->exp_lock);
if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
/* Someone else doing GP, so wait for them. */
spin_unlock(&rnp->exp_lock);
trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
rnp->grplo, rnp->grphi,
TPS("wait"));
wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
sync_exp_work_done(s));
return true;
}
WRITE_ONCE(rnp->exp_seq_rq, s); /* Followers can wait on us. */
spin_unlock(&rnp->exp_lock);
trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
rnp->grplo, rnp->grphi, TPS("nxtlvl"));
}
mutex_lock(&rcu_state.exp_mutex);
fastpath:
if (sync_exp_work_done(s)) {
mutex_unlock(&rcu_state.exp_mutex);
return true;
}
rcu_exp_gp_seq_start();
trace_rcu_exp_grace_period(rcu_state.name, s, TPS("start"));
return false;
}
/*
* Select the CPUs within the specified rcu_node that the upcoming
* expedited grace period needs to wait for.
*/
static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp)
{
int cpu;
unsigned long flags;
unsigned long mask_ofl_test;
unsigned long mask_ofl_ipi;
int ret;
struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew);
raw_spin_lock_irqsave_rcu_node(rnp, flags);
/* Each pass checks a CPU for identity, offline, and idle. */
mask_ofl_test = 0;
for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
unsigned long mask = rdp->grpmask;
int snap;
if (raw_smp_processor_id() == cpu ||
!(rnp->qsmaskinitnext & mask)) {
mask_ofl_test |= mask;
} else {
/*
* Full ordering between remote CPU's post idle accesses
* and updater's accesses prior to current GP (and also
* the started GP sequence number) is enforced by
* rcu_seq_start() implicit barrier, relayed by kworkers
* locking and even further by smp_mb__after_unlock_lock()
* barriers chained all the way throughout the rnp locking
* tree since sync_exp_reset_tree() and up to the current
* leaf rnp locking.
*
* Ordering between remote CPU's pre idle accesses and
* post grace period updater's accesses is enforced by the
* below acquire semantic.
*/
snap = ct_rcu_watching_cpu_acquire(cpu);
if (rcu_watching_snap_in_eqs(snap))
mask_ofl_test |= mask;
else
rdp->exp_watching_snap = snap;
}
}
mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
/*
* Need to wait for any blocked tasks as well. Note that
* additional blocking tasks will also block the expedited GP
* until such time as the ->expmask bits are cleared.
*/
if (rcu_preempt_has_tasks(rnp))
WRITE_ONCE(rnp->exp_tasks, rnp->blkd_tasks.next);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
/* IPI the remaining CPUs for expedited quiescent state. */
for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) {
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
unsigned long mask = rdp->grpmask;
retry_ipi:
if (rcu_watching_snap_stopped_since(rdp, rdp->exp_watching_snap)) {
mask_ofl_test |= mask;
continue;
}
if (get_cpu() == cpu) {
mask_ofl_test |= mask;
put_cpu();
continue;
}
ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
put_cpu();
/* The CPU will report the QS in response to the IPI. */
if (!ret)
continue;
/* Failed, raced with CPU hotplug operation. */
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if ((rnp->qsmaskinitnext & mask) &&
(rnp->expmask & mask)) {
/* Online, so delay for a bit and try again. */
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("selectofl"));
schedule_timeout_idle(1);
goto retry_ipi;
}
/* CPU really is offline, so we must report its QS. */
if (rnp->expmask & mask)
mask_ofl_test |= mask;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
/* Report quiescent states for those that went offline. */
if (mask_ofl_test)
rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
}
static void rcu_exp_sel_wait_wake(unsigned long s);
static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp)
{
struct rcu_exp_work *rewp =
container_of(wp, struct rcu_exp_work, rew_work);
__sync_rcu_exp_select_node_cpus(rewp);
}
static inline bool rcu_exp_worker_started(void)
{
return !!READ_ONCE(rcu_exp_gp_kworker);
}
static inline bool rcu_exp_par_worker_started(struct rcu_node *rnp)
{
return !!READ_ONCE(rnp->exp_kworker);
}
static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
{
kthread_init_work(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
/*
* Use rcu_exp_par_gp_kworker, because flushing a work item from
* another work item on the same kthread worker can result in
* deadlock.
*/
kthread_queue_work(READ_ONCE(rnp->exp_kworker), &rnp->rew.rew_work);
}
static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
{
kthread_flush_work(&rnp->rew.rew_work);
}
/*
* Work-queue handler to drive an expedited grace period forward.
*/
static void wait_rcu_exp_gp(struct kthread_work *wp)
{
struct rcu_exp_work *rewp;
rewp = container_of(wp, struct rcu_exp_work, rew_work);
rcu_exp_sel_wait_wake(rewp->rew_s);
}
static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
{
kthread_init_work(&rew->rew_work, wait_rcu_exp_gp);
kthread_queue_work(rcu_exp_gp_kworker, &rew->rew_work);
}
/*
* Select the nodes that the upcoming expedited grace period needs
* to wait for.
*/
static void sync_rcu_exp_select_cpus(void)
{
struct rcu_node *rnp;
trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset"));
sync_exp_reset_tree();
trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select"));
/* Schedule work for each leaf rcu_node structure. */
rcu_for_each_leaf_node(rnp) {
rnp->exp_need_flush = false;
if (!READ_ONCE(rnp->expmask))
continue; /* Avoid early boot non-existent wq. */
if (!rcu_exp_par_worker_started(rnp) ||
rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
rcu_is_last_leaf_node(rnp)) {
/* No worker started yet or last leaf, do direct call. */
sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
continue;
}
sync_rcu_exp_select_cpus_queue_work(rnp);
rnp->exp_need_flush = true;
}
/* Wait for jobs (if any) to complete. */
rcu_for_each_leaf_node(rnp)
if (rnp->exp_need_flush)
sync_rcu_exp_select_cpus_flush_work(rnp);
}
/*
* Wait for the expedited grace period to elapse, within time limit.
* If the time limit is exceeded without the grace period elapsing,
* return false, otherwise return true.
*/
static bool synchronize_rcu_expedited_wait_once(long tlimit)
{
int t;
struct rcu_node *rnp_root = rcu_get_root();
t = swait_event_timeout_exclusive(rcu_state.expedited_wq,
sync_rcu_exp_done_unlocked(rnp_root),
tlimit);
// Workqueues should not be signaled.
if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root))
return true;
WARN_ON(t < 0); /* workqueues should not be signaled. */
return false;
}
/*
* Print out an expedited RCU CPU stall warning message.
*/
static void synchronize_rcu_expedited_stall(unsigned long jiffies_start, unsigned long j)
{
int cpu;
unsigned long mask;
int ndetected;
struct rcu_node *rnp;
struct rcu_node *rnp_root = rcu_get_root();
if (READ_ONCE(csd_lock_suppress_rcu_stall) && csd_lock_is_stuck()) {
pr_err("INFO: %s detected expedited stalls, but suppressed full report due to a stuck CSD-lock.\n", rcu_state.name);
return;
}
pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {", rcu_state.name);
ndetected = 0;
rcu_for_each_leaf_node(rnp) {
ndetected += rcu_print_task_exp_stall(rnp);
for_each_leaf_node_possible_cpu(rnp, cpu) {
struct rcu_data *rdp;
mask = leaf_node_cpu_bit(rnp, cpu);
if (!(READ_ONCE(rnp->expmask) & mask))
continue;
ndetected++;
rdp = per_cpu_ptr(&rcu_data, cpu);
pr_cont(" %d-%c%c%c%c", cpu,
"O."[!!cpu_online(cpu)],
"o."[!!(rdp->grpmask & rnp->expmaskinit)],
"N."[!!(rdp->grpmask & rnp->expmaskinitnext)],
"D."[!!data_race(rdp->cpu_no_qs.b.exp)]);
}
}
pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
j - jiffies_start, rcu_state.expedited_sequence, data_race(rnp_root->expmask),
".T"[!!data_race(rnp_root->exp_tasks)]);
if (ndetected) {
pr_err("blocking rcu_node structures (internal RCU debug):");
rcu_for_each_node_breadth_first(rnp) {
if (rnp == rnp_root)
continue; /* printed unconditionally */
if (sync_rcu_exp_done_unlocked(rnp))
continue;
pr_cont(" l=%u:%d-%d:%#lx/%c",
rnp->level, rnp->grplo, rnp->grphi, data_race(rnp->expmask),
".T"[!!data_race(rnp->exp_tasks)]);
}
pr_cont("\n");
}
rcu_for_each_leaf_node(rnp) {
for_each_leaf_node_possible_cpu(rnp, cpu) {
mask = leaf_node_cpu_bit(rnp, cpu);
if (!(READ_ONCE(rnp->expmask) & mask))
continue;
dump_cpu_task(cpu);
}
rcu_exp_print_detail_task_stall_rnp(rnp);
}
}
/*
* Wait for the expedited grace period to elapse, issuing any needed
* RCU CPU stall warnings along the way.
*/
static void synchronize_rcu_expedited_wait(void)
{
int cpu;
unsigned long j;
unsigned long jiffies_stall;
unsigned long jiffies_start;
unsigned long mask;
struct rcu_data *rdp;
struct rcu_node *rnp;
unsigned long flags;
trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
jiffies_stall = rcu_exp_jiffies_till_stall_check();
jiffies_start = jiffies;
if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) {
if (synchronize_rcu_expedited_wait_once(1))
return;
rcu_for_each_leaf_node(rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
mask = READ_ONCE(rnp->expmask);
for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
rdp = per_cpu_ptr(&rcu_data, cpu);
if (rdp->rcu_forced_tick_exp)
continue;
rdp->rcu_forced_tick_exp = true;
if (cpu_online(cpu))
tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
j = READ_ONCE(jiffies_till_first_fqs);
if (synchronize_rcu_expedited_wait_once(j + HZ))
return;
}
for (;;) {
unsigned long j;
if (synchronize_rcu_expedited_wait_once(jiffies_stall))
return;
if (rcu_stall_is_suppressed())
continue;
nbcon_cpu_emergency_enter();
j = jiffies;
rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_EXP, (void *)(j - jiffies_start));
trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
synchronize_rcu_expedited_stall(jiffies_start, j);
jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
nbcon_cpu_emergency_exit();
panic_on_rcu_stall();
}
}
/*
* Wait for the current expedited grace period to complete, and then
* wake up everyone who piggybacked on the just-completed expedited
* grace period. Also update all the ->exp_seq_rq counters as needed
* in order to avoid counter-wrap problems.
*/
static void rcu_exp_wait_wake(unsigned long s)
{
struct rcu_node *rnp;
synchronize_rcu_expedited_wait();
// Switch over to wakeup mode, allowing the next GP to proceed.
// End the previous grace period only after acquiring the mutex
// to ensure that only one GP runs concurrently with wakeups.
mutex_lock(&rcu_state.exp_wake_mutex);
rcu_exp_gp_seq_end();
trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end"));
rcu_for_each_node_breadth_first(rnp) {
if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
spin_lock(&rnp->exp_lock);
/* Recheck, avoid hang in case someone just arrived. */
if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
WRITE_ONCE(rnp->exp_seq_rq, s);
spin_unlock(&rnp->exp_lock);
}
smp_mb(); /* All above changes before wakeup. */
wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]);
}
trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake"));
mutex_unlock(&rcu_state.exp_wake_mutex);
}
/*
* Common code to drive an expedited grace period forward, used by
* workqueues and mid-boot-time tasks.
*/
static void rcu_exp_sel_wait_wake(unsigned long s)
{
/* Initialize the rcu_node tree in preparation for the wait. */
sync_rcu_exp_select_cpus();
/* Wait and clean up, including waking everyone. */
rcu_exp_wait_wake(s);
}
#ifdef CONFIG_PREEMPT_RCU
/*
* Remote handler for smp_call_function_single(). If there is an
* RCU read-side critical section in effect, request that the
* next rcu_read_unlock() record the quiescent state up the
* ->expmask fields in the rcu_node tree. Otherwise, immediately
* report the quiescent state.
*/
static void rcu_exp_handler(void *unused)
{
int depth = rcu_preempt_depth();
unsigned long flags;
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode;
struct task_struct *t = current;
/*
* First, the common case of not being in an RCU read-side
* critical section. If also enabled or idle, immediately
* report the quiescent state, otherwise defer.
*/
if (!depth) {
if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
rcu_is_cpu_rrupt_from_idle()) {
rcu_report_exp_rdp(rdp);
} else {
WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
set_tsk_need_resched(t);
set_preempt_need_resched();
}
return;
}
/*
* Second, the less-common case of being in an RCU read-side
* critical section. In this case we can count on a future
* rcu_read_unlock(). However, this rcu_read_unlock() might
* execute on some other CPU, but in that case there will be
* a future context switch. Either way, if the expedited
* grace period is still waiting on this CPU, set ->deferred_qs
* so that the eventual quiescent state will be reported.
* Note that there is a large group of race conditions that
* can have caused this quiescent state to already have been
* reported, so we really do need to check ->expmask.
*/
if (depth > 0) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rnp->expmask & rdp->grpmask) {
WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
t->rcu_read_unlock_special.b.exp_hint = true;
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
// Finally, negative nesting depth should not happen.
WARN_ON_ONCE(1);
}
/* PREEMPTION=y, so no PREEMPTION=n expedited grace period to clean up after. */
static void sync_sched_exp_online_cleanup(int cpu)
{
}
/*
* Scan the current list of tasks blocked within RCU read-side critical
* sections, printing out the tid of each that is blocking the current
* expedited grace period.
*/
static int rcu_print_task_exp_stall(struct rcu_node *rnp)
{
unsigned long flags;
int ndetected = 0;
struct task_struct *t;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (!rnp->exp_tasks) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return 0;
}
t = list_entry(rnp->exp_tasks->prev,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
pr_cont(" P%d", t->pid);
ndetected++;
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return ndetected;
}
/*
* Scan the current list of tasks blocked within RCU read-side critical
* sections, dumping the stack of each that is blocking the current
* expedited grace period.
*/
static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
unsigned long flags;
struct task_struct *t;
if (!rcu_exp_stall_task_details)
return;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (!READ_ONCE(rnp->exp_tasks)) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
t = list_entry(rnp->exp_tasks->prev,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
/*
* We could be printing a lot while holding a spinlock.
* Avoid triggering hard lockup.
*/
touch_nmi_watchdog();
sched_show_task(t);
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
#else /* #ifdef CONFIG_PREEMPT_RCU */
/* Request an expedited quiescent state. */
static void rcu_exp_need_qs(void)
{
__this_cpu_write(rcu_data.cpu_no_qs.b.exp, true);
/* Store .exp before .rcu_urgent_qs. */
smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true);
set_tsk_need_resched(current);
set_preempt_need_resched();
}
/* Invoked on each online non-idle CPU for expedited quiescent state. */
static void rcu_exp_handler(void *unused)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode;
bool preempt_bh_enabled = !(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
return;
if (rcu_is_cpu_rrupt_from_idle() ||
(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preempt_bh_enabled)) {
rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
return;
}
rcu_exp_need_qs();
}
/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
static void sync_sched_exp_online_cleanup(int cpu)
{
unsigned long flags;
int my_cpu;
struct rcu_data *rdp;
int ret;
struct rcu_node *rnp;
rdp = per_cpu_ptr(&rcu_data, cpu);
rnp = rdp->mynode;
my_cpu = get_cpu();
/* Quiescent state either not needed or already requested, leave. */
if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
READ_ONCE(rdp->cpu_no_qs.b.exp)) {
put_cpu();
return;
}
/* Quiescent state needed on current CPU, so set it up locally. */
if (my_cpu == cpu) {
local_irq_save(flags);
rcu_exp_need_qs();
local_irq_restore(flags);
put_cpu();
return;
}
/* Quiescent state needed on some other CPU, send IPI. */
ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
put_cpu();
WARN_ON_ONCE(ret);
}
/*
* Because preemptible RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections that are
* blocking the current expedited grace period.
*/
static int rcu_print_task_exp_stall(struct rcu_node *rnp)
{
return 0;
}
/*
* Because preemptible RCU does not exist, we never have to print out
* tasks blocked within RCU read-side critical sections that are blocking
* the current expedited grace period.
*/
static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
}
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
/**
* synchronize_rcu_expedited - Brute-force RCU grace period
*
* Wait for an RCU grace period, but expedite it. The basic idea is to
* IPI all non-idle non-nohz online CPUs. The IPI handler checks whether
* the CPU is in an RCU critical section, and if so, it sets a flag that
* causes the outermost rcu_read_unlock() to report the quiescent state
* for RCU-preempt or asks the scheduler for help for RCU-sched. On the
* other hand, if the CPU is not in an RCU read-side critical section,
* the IPI handler reports the quiescent state immediately.
*
* Although this is a great improvement over previous expedited
* implementations, it is still unfriendly to real-time workloads, so is
* thus not recommended for any sort of common-case code. In fact, if
* you are using synchronize_rcu_expedited() in a loop, please restructure
* your code to batch your updates, and then use a single synchronize_rcu()
* instead.
*
* This has the same semantics as (but is more brutal than) synchronize_rcu().
*/
void synchronize_rcu_expedited(void)
{
unsigned long flags;
struct rcu_exp_work rew;
struct rcu_node *rnp;
unsigned long s;
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
lock_is_held(&rcu_lock_map) ||
lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_rcu_expedited() in RCU read-side critical section");
/* Is the state is such that the call is a grace period? */
if (rcu_blocking_is_gp()) {
// Note well that this code runs with !PREEMPT && !SMP.
// In addition, all code that advances grace periods runs
// at process level. Therefore, this expedited GP overlaps
// with other expedited GPs only by being fully nested within
// them, which allows reuse of ->gp_seq_polled_exp_snap.
rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
local_irq_save(flags);
WARN_ON_ONCE(num_online_cpus() > 1);
rcu_state.expedited_sequence += (1 << RCU_SEQ_CTR_SHIFT);
local_irq_restore(flags);
return; // Context allows vacuous grace periods.
}
/* If expedited grace periods are prohibited, fall back to normal. */
if (rcu_gp_is_normal()) {
synchronize_rcu_normal();
return;
}
/* Take a snapshot of the sequence number. */
s = rcu_exp_gp_seq_snap();
if (exp_funnel_lock(s))
return; /* Someone else did our work for us. */
/* Ensure that load happens before action based on it. */
if (unlikely((rcu_scheduler_active == RCU_SCHEDULER_INIT) || !rcu_exp_worker_started())) {
/* Direct call during scheduler init and early_initcalls(). */
rcu_exp_sel_wait_wake(s);
} else {
/* Marshall arguments & schedule the expedited grace period. */
rew.rew_s = s;
synchronize_rcu_expedited_queue_work(&rew);
}
/* Wait for expedited grace period to complete. */
rnp = rcu_get_root();
wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
sync_exp_work_done(s));
/* Let the next expedited grace period start. */
mutex_unlock(&rcu_state.exp_mutex);
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
/*
* Ensure that start_poll_synchronize_rcu_expedited() has the expedited
* RCU grace periods that it needs.
*/
static void sync_rcu_do_polled_gp(struct work_struct *wp)
{
unsigned long flags;
int i = 0;
struct rcu_node *rnp = container_of(wp, struct rcu_node, exp_poll_wq);
unsigned long s;
raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
s = rnp->exp_seq_poll_rq;
rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
if (s == RCU_GET_STATE_COMPLETED)
return;
while (!poll_state_synchronize_rcu(s)) {
synchronize_rcu_expedited();
if (i == 10 || i == 20)
pr_info("%s: i = %d s = %lx gp_seq_polled = %lx\n", __func__, i, s, READ_ONCE(rcu_state.gp_seq_polled));
i++;
}
raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
s = rnp->exp_seq_poll_rq;
if (poll_state_synchronize_rcu(s))
rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
}
/**
* start_poll_synchronize_rcu_expedited - Snapshot current RCU state and start expedited grace period
*
* Returns a cookie to pass to a call to cond_synchronize_rcu(),
* cond_synchronize_rcu_expedited(), or poll_state_synchronize_rcu(),
* allowing them to determine whether or not any sort of grace period has
* elapsed in the meantime. If the needed expedited grace period is not
* already slated to start, initiates that grace period.
*/
unsigned long start_poll_synchronize_rcu_expedited(void)
{
unsigned long flags;
struct rcu_data *rdp;
struct rcu_node *rnp;
unsigned long s;
s = get_state_synchronize_rcu();
rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
rnp = rdp->mynode;
if (rcu_init_invoked())
raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
if (!poll_state_synchronize_rcu(s)) {
if (rcu_init_invoked()) {
rnp->exp_seq_poll_rq = s;
queue_work(rcu_gp_wq, &rnp->exp_poll_wq);
}
}
if (rcu_init_invoked())
raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
return s;
}
EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited);
/**
* start_poll_synchronize_rcu_expedited_full - Take a full snapshot and start expedited grace period
* @rgosp: Place to put snapshot of grace-period state
*
* Places the normal and expedited grace-period states in rgosp. This
* state value can be passed to a later call to cond_synchronize_rcu_full()
* or poll_state_synchronize_rcu_full() to determine whether or not a
* grace period (whether normal or expedited) has elapsed in the meantime.
* If the needed expedited grace period is not already slated to start,
* initiates that grace period.
*/
void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
{
get_state_synchronize_rcu_full(rgosp);
(void)start_poll_synchronize_rcu_expedited();
}
EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited_full);
/**
* cond_synchronize_rcu_expedited - Conditionally wait for an expedited RCU grace period
*
* @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
*
* If any type of full RCU grace period has elapsed since the earlier
* call to get_state_synchronize_rcu(), start_poll_synchronize_rcu(),
* or start_poll_synchronize_rcu_expedited(), just return. Otherwise,
* invoke synchronize_rcu_expedited() to wait for a full grace period.
*
* Yes, this function does not take counter wrap into account.
* But counter wrap is harmless. If the counter wraps, we have waited for
* more than 2 billion grace periods (and way more on a 64-bit system!),
* so waiting for a couple of additional grace periods should be just fine.
*
* This function provides the same memory-ordering guarantees that
* would be provided by a synchronize_rcu() that was invoked at the call
* to the function that provided @oldstate and that returned at the end
* of this function.
*/
void cond_synchronize_rcu_expedited(unsigned long oldstate)
{
if (!poll_state_synchronize_rcu(oldstate))
synchronize_rcu_expedited();
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited);
/**
* cond_synchronize_rcu_expedited_full - Conditionally wait for an expedited RCU grace period
* @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
*
* If a full RCU grace period has elapsed since the call to
* get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
* or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
* obtained, just return. Otherwise, invoke synchronize_rcu_expedited()
* to wait for a full grace period.
*
* Yes, this function does not take counter wrap into account.
* But counter wrap is harmless. If the counter wraps, we have waited for
* more than 2 billion grace periods (and way more on a 64-bit system!),
* so waiting for a couple of additional grace periods should be just fine.
*
* This function provides the same memory-ordering guarantees that
* would be provided by a synchronize_rcu() that was invoked at the call
* to the function that provided @rgosp and that returned at the end of
* this function.
*/
void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
{
if (!poll_state_synchronize_rcu_full(rgosp))
synchronize_rcu_expedited();
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited_full);
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