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rcutree.c
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rcutree.c
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/*
* Read-Copy Update mechanism for mutual exclusion
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright IBM Corporation, 2008
*
* Authors: Dipankar Sarma <dipankar@in.ibm.com>
* Manfred Spraul <manfred@colorfullife.com>
* Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
*
* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
*
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/rcupdate.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <asm/atomic.h>
#include <linux/bitops.h>
#include <linux/module.h>
#include <linux/completion.h>
#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/time.h>
#ifdef CONFIG_DEBUG_LOCK_ALLOC
static struct lock_class_key rcu_lock_key;
struct lockdep_map rcu_lock_map =
STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
EXPORT_SYMBOL_GPL(rcu_lock_map);
#endif
/* Data structures. */
#define RCU_STATE_INITIALIZER(name) { \
.level = { &name.node[0] }, \
.levelcnt = { \
NUM_RCU_LVL_0, /* root of hierarchy. */ \
NUM_RCU_LVL_1, \
NUM_RCU_LVL_2, \
NUM_RCU_LVL_3, /* == MAX_RCU_LVLS */ \
}, \
.signaled = RCU_SIGNAL_INIT, \
.gpnum = -300, \
.completed = -300, \
.onofflock = __SPIN_LOCK_UNLOCKED(&name.onofflock), \
.fqslock = __SPIN_LOCK_UNLOCKED(&name.fqslock), \
.n_force_qs = 0, \
.n_force_qs_ngp = 0, \
}
struct rcu_state rcu_state = RCU_STATE_INITIALIZER(rcu_state);
DEFINE_PER_CPU(struct rcu_data, rcu_data);
struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
#ifdef CONFIG_NO_HZ
DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
.dynticks_nesting = 1,
.dynticks = 1,
};
#endif /* #ifdef CONFIG_NO_HZ */
static int blimit = 10; /* Maximum callbacks per softirq. */
static int qhimark = 10000; /* If this many pending, ignore blimit. */
static int qlowmark = 100; /* Once only this many pending, use blimit. */
static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
/*
* Return the number of RCU batches processed thus far for debug & stats.
*/
long rcu_batches_completed(void)
{
return rcu_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);
/*
* Return the number of RCU BH batches processed thus far for debug & stats.
*/
long rcu_batches_completed_bh(void)
{
return rcu_bh_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
/*
* Does the CPU have callbacks ready to be invoked?
*/
static int
cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
{
return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
}
/*
* Does the current CPU require a yet-as-unscheduled grace period?
*/
static int
cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
{
/* ACCESS_ONCE() because we are accessing outside of lock. */
return *rdp->nxttail[RCU_DONE_TAIL] &&
ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum);
}
/*
* Return the root node of the specified rcu_state structure.
*/
static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
{
return &rsp->node[0];
}
#ifdef CONFIG_SMP
/*
* If the specified CPU is offline, tell the caller that it is in
* a quiescent state. Otherwise, whack it with a reschedule IPI.
* Grace periods can end up waiting on an offline CPU when that
* CPU is in the process of coming online -- it will be added to the
* rcu_node bitmasks before it actually makes it online. The same thing
* can happen while a CPU is in the process of coming online. Because this
* race is quite rare, we check for it after detecting that the grace
* period has been delayed rather than checking each and every CPU
* each and every time we start a new grace period.
*/
static int rcu_implicit_offline_qs(struct rcu_data *rdp)
{
/*
* If the CPU is offline, it is in a quiescent state. We can
* trust its state not to change because interrupts are disabled.
*/
if (cpu_is_offline(rdp->cpu)) {
rdp->offline_fqs++;
return 1;
}
/* The CPU is online, so send it a reschedule IPI. */
if (rdp->cpu != smp_processor_id())
smp_send_reschedule(rdp->cpu);
else
set_need_resched();
rdp->resched_ipi++;
return 0;
}
#endif /* #ifdef CONFIG_SMP */
#ifdef CONFIG_NO_HZ
static DEFINE_RATELIMIT_STATE(rcu_rs, 10 * HZ, 5);
/**
* rcu_enter_nohz - inform RCU that current CPU is entering nohz
*
* Enter nohz mode, in other words, -leave- the mode in which RCU
* read-side critical sections can occur. (Though RCU read-side
* critical sections can occur in irq handlers in nohz mode, a possibility
* handled by rcu_irq_enter() and rcu_irq_exit()).
*/
void rcu_enter_nohz(void)
{
unsigned long flags;
struct rcu_dynticks *rdtp;
smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
local_irq_save(flags);
rdtp = &__get_cpu_var(rcu_dynticks);
rdtp->dynticks++;
rdtp->dynticks_nesting--;
WARN_ON_RATELIMIT(rdtp->dynticks & 0x1, &rcu_rs);
local_irq_restore(flags);
}
/*
* rcu_exit_nohz - inform RCU that current CPU is leaving nohz
*
* Exit nohz mode, in other words, -enter- the mode in which RCU
* read-side critical sections normally occur.
*/
void rcu_exit_nohz(void)
{
unsigned long flags;
struct rcu_dynticks *rdtp;
local_irq_save(flags);
rdtp = &__get_cpu_var(rcu_dynticks);
rdtp->dynticks++;
rdtp->dynticks_nesting++;
WARN_ON_RATELIMIT(!(rdtp->dynticks & 0x1), &rcu_rs);
local_irq_restore(flags);
smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
}
/**
* rcu_nmi_enter - inform RCU of entry to NMI context
*
* If the CPU was idle with dynamic ticks active, and there is no
* irq handler running, this updates rdtp->dynticks_nmi to let the
* RCU grace-period handling know that the CPU is active.
*/
void rcu_nmi_enter(void)
{
struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
if (rdtp->dynticks & 0x1)
return;
rdtp->dynticks_nmi++;
WARN_ON_RATELIMIT(!(rdtp->dynticks_nmi & 0x1), &rcu_rs);
smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
}
/**
* rcu_nmi_exit - inform RCU of exit from NMI context
*
* If the CPU was idle with dynamic ticks active, and there is no
* irq handler running, this updates rdtp->dynticks_nmi to let the
* RCU grace-period handling know that the CPU is no longer active.
*/
void rcu_nmi_exit(void)
{
struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
if (rdtp->dynticks & 0x1)
return;
smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
rdtp->dynticks_nmi++;
WARN_ON_RATELIMIT(rdtp->dynticks_nmi & 0x1, &rcu_rs);
}
/**
* rcu_irq_enter - inform RCU of entry to hard irq context
*
* If the CPU was idle with dynamic ticks active, this updates the
* rdtp->dynticks to let the RCU handling know that the CPU is active.
*/
void rcu_irq_enter(void)
{
struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
if (rdtp->dynticks_nesting++)
return;
rdtp->dynticks++;
WARN_ON_RATELIMIT(!(rdtp->dynticks & 0x1), &rcu_rs);
smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
}
/**
* rcu_irq_exit - inform RCU of exit from hard irq context
*
* If the CPU was idle with dynamic ticks active, update the rdp->dynticks
* to put let the RCU handling be aware that the CPU is going back to idle
* with no ticks.
*/
void rcu_irq_exit(void)
{
struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
if (--rdtp->dynticks_nesting)
return;
smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
rdtp->dynticks++;
WARN_ON_RATELIMIT(rdtp->dynticks & 0x1, &rcu_rs);
/* If the interrupt queued a callback, get out of dyntick mode. */
if (__get_cpu_var(rcu_data).nxtlist ||
__get_cpu_var(rcu_bh_data).nxtlist)
set_need_resched();
}
/*
* Record the specified "completed" value, which is later used to validate
* dynticks counter manipulations. Specify "rsp->completed - 1" to
* unconditionally invalidate any future dynticks manipulations (which is
* useful at the beginning of a grace period).
*/
static void dyntick_record_completed(struct rcu_state *rsp, long comp)
{
rsp->dynticks_completed = comp;
}
#ifdef CONFIG_SMP
/*
* Recall the previously recorded value of the completion for dynticks.
*/
static long dyntick_recall_completed(struct rcu_state *rsp)
{
return rsp->dynticks_completed;
}
/*
* Snapshot the specified CPU's dynticks counter so that we can later
* credit them with an implicit quiescent state. Return 1 if this CPU
* is already in a quiescent state courtesy of dynticks idle mode.
*/
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
int ret;
int snap;
int snap_nmi;
snap = rdp->dynticks->dynticks;
snap_nmi = rdp->dynticks->dynticks_nmi;
smp_mb(); /* Order sampling of snap with end of grace period. */
rdp->dynticks_snap = snap;
rdp->dynticks_nmi_snap = snap_nmi;
ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0);
if (ret)
rdp->dynticks_fqs++;
return ret;
}
/*
* Return true if the specified CPU has passed through a quiescent
* state by virtue of being in or having passed through an dynticks
* idle state since the last call to dyntick_save_progress_counter()
* for this same CPU.
*/
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
{
long curr;
long curr_nmi;
long snap;
long snap_nmi;
curr = rdp->dynticks->dynticks;
snap = rdp->dynticks_snap;
curr_nmi = rdp->dynticks->dynticks_nmi;
snap_nmi = rdp->dynticks_nmi_snap;
smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
/*
* If the CPU passed through or entered a dynticks idle phase with
* no active irq/NMI handlers, then we can safely pretend that the CPU
* already acknowledged the request to pass through a quiescent
* state. Either way, that CPU cannot possibly be in an RCU
* read-side critical section that started before the beginning
* of the current RCU grace period.
*/
if ((curr != snap || (curr & 0x1) == 0) &&
(curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) {
rdp->dynticks_fqs++;
return 1;
}
/* Go check for the CPU being offline. */
return rcu_implicit_offline_qs(rdp);
}
#endif /* #ifdef CONFIG_SMP */
#else /* #ifdef CONFIG_NO_HZ */
static void dyntick_record_completed(struct rcu_state *rsp, long comp)
{
}
#ifdef CONFIG_SMP
/*
* If there are no dynticks, then the only way that a CPU can passively
* be in a quiescent state is to be offline. Unlike dynticks idle, which
* is a point in time during the prior (already finished) grace period,
* an offline CPU is always in a quiescent state, and thus can be
* unconditionally applied. So just return the current value of completed.
*/
static long dyntick_recall_completed(struct rcu_state *rsp)
{
return rsp->completed;
}
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
return 0;
}
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
{
return rcu_implicit_offline_qs(rdp);
}
#endif /* #ifdef CONFIG_SMP */
#endif /* #else #ifdef CONFIG_NO_HZ */
#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
static void record_gp_stall_check_time(struct rcu_state *rsp)
{
rsp->gp_start = jiffies;
rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
}
static void print_other_cpu_stall(struct rcu_state *rsp)
{
int cpu;
long delta;
unsigned long flags;
struct rcu_node *rnp = rcu_get_root(rsp);
struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];
/* Only let one CPU complain about others per time interval. */
spin_lock_irqsave(&rnp->lock, flags);
delta = jiffies - rsp->jiffies_stall;
if (delta < RCU_STALL_RAT_DELAY || rsp->gpnum == rsp->completed) {
spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
spin_unlock_irqrestore(&rnp->lock, flags);
/* OK, time to rat on our buddy... */
printk(KERN_ERR "INFO: RCU detected CPU stalls:");
for (; rnp_cur < rnp_end; rnp_cur++) {
if (rnp_cur->qsmask == 0)
continue;
for (cpu = 0; cpu <= rnp_cur->grphi - rnp_cur->grplo; cpu++)
if (rnp_cur->qsmask & (1UL << cpu))
printk(" %d", rnp_cur->grplo + cpu);
}
printk(" (detected by %d, t=%ld jiffies)\n",
smp_processor_id(), (long)(jiffies - rsp->gp_start));
force_quiescent_state(rsp, 0); /* Kick them all. */
}
static void print_cpu_stall(struct rcu_state *rsp)
{
unsigned long flags;
struct rcu_node *rnp = rcu_get_root(rsp);
printk(KERN_ERR "INFO: RCU detected CPU %d stall (t=%lu jiffies)\n",
smp_processor_id(), jiffies - rsp->gp_start);
dump_stack();
spin_lock_irqsave(&rnp->lock, flags);
if ((long)(jiffies - rsp->jiffies_stall) >= 0)
rsp->jiffies_stall =
jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
spin_unlock_irqrestore(&rnp->lock, flags);
set_need_resched(); /* kick ourselves to get things going. */
}
static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
long delta;
struct rcu_node *rnp;
delta = jiffies - rsp->jiffies_stall;
rnp = rdp->mynode;
if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
/* We haven't checked in, so go dump stack. */
print_cpu_stall(rsp);
} else if (rsp->gpnum != rsp->completed &&
delta >= RCU_STALL_RAT_DELAY) {
/* They had two time units to dump stack, so complain. */
print_other_cpu_stall(rsp);
}
}
#else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
static void record_gp_stall_check_time(struct rcu_state *rsp)
{
}
static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
}
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
/*
* Update CPU-local rcu_data state to record the newly noticed grace period.
* This is used both when we started the grace period and when we notice
* that someone else started the grace period.
*/
static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
{
rdp->qs_pending = 1;
rdp->passed_quiesc = 0;
rdp->gpnum = rsp->gpnum;
rdp->n_rcu_pending_force_qs = rdp->n_rcu_pending +
RCU_JIFFIES_TILL_FORCE_QS;
}
/*
* Did someone else start a new RCU grace period start since we last
* checked? Update local state appropriately if so. Must be called
* on the CPU corresponding to rdp.
*/
static int
check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
int ret = 0;
local_irq_save(flags);
if (rdp->gpnum != rsp->gpnum) {
note_new_gpnum(rsp, rdp);
ret = 1;
}
local_irq_restore(flags);
return ret;
}
/*
* Start a new RCU grace period if warranted, re-initializing the hierarchy
* in preparation for detecting the next grace period. The caller must hold
* the root node's ->lock, which is released before return. Hard irqs must
* be disabled.
*/
static void
rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
__releases(rcu_get_root(rsp)->lock)
{
struct rcu_data *rdp = rsp->rda[smp_processor_id()];
struct rcu_node *rnp = rcu_get_root(rsp);
struct rcu_node *rnp_cur;
struct rcu_node *rnp_end;
if (!cpu_needs_another_gp(rsp, rdp)) {
spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
/* Advance to a new grace period and initialize state. */
rsp->gpnum++;
rsp->signaled = RCU_GP_INIT; /* Hold off force_quiescent_state. */
rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
rdp->n_rcu_pending_force_qs = rdp->n_rcu_pending +
RCU_JIFFIES_TILL_FORCE_QS;
record_gp_stall_check_time(rsp);
dyntick_record_completed(rsp, rsp->completed - 1);
note_new_gpnum(rsp, rdp);
/*
* Because we are first, we know that all our callbacks will
* be covered by this upcoming grace period, even the ones
* that were registered arbitrarily recently.
*/
rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
/* Special-case the common single-level case. */
if (NUM_RCU_NODES == 1) {
rnp->qsmask = rnp->qsmaskinit;
rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
spin_unlock(&rnp->lock); /* leave irqs disabled. */
/* Exclude any concurrent CPU-hotplug operations. */
spin_lock(&rsp->onofflock); /* irqs already disabled. */
/*
* Set the quiescent-state-needed bits in all the non-leaf RCU
* nodes for all currently online CPUs. This operation relies
* on the layout of the hierarchy within the rsp->node[] array.
* Note that other CPUs will access only the leaves of the
* hierarchy, which still indicate that no grace period is in
* progress. In addition, we have excluded CPU-hotplug operations.
*
* We therefore do not need to hold any locks. Any required
* memory barriers will be supplied by the locks guarding the
* leaf rcu_nodes in the hierarchy.
*/
rnp_end = rsp->level[NUM_RCU_LVLS - 1];
for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++)
rnp_cur->qsmask = rnp_cur->qsmaskinit;
/*
* Now set up the leaf nodes. Here we must be careful. First,
* we need to hold the lock in order to exclude other CPUs, which
* might be contending for the leaf nodes' locks. Second, as
* soon as we initialize a given leaf node, its CPUs might run
* up the rest of the hierarchy. We must therefore acquire locks
* for each node that we touch during this stage. (But we still
* are excluding CPU-hotplug operations.)
*
* Note that the grace period cannot complete until we finish
* the initialization process, as there will be at least one
* qsmask bit set in the root node until that time, namely the
* one corresponding to this CPU.
*/
rnp_end = &rsp->node[NUM_RCU_NODES];
rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
for (; rnp_cur < rnp_end; rnp_cur++) {
spin_lock(&rnp_cur->lock); /* irqs already disabled. */
rnp_cur->qsmask = rnp_cur->qsmaskinit;
spin_unlock(&rnp_cur->lock); /* irqs already disabled. */
}
rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
spin_unlock_irqrestore(&rsp->onofflock, flags);
}
/*
* Advance this CPU's callbacks, but only if the current grace period
* has ended. This may be called only from the CPU to whom the rdp
* belongs.
*/
static void
rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
{
long completed_snap;
unsigned long flags;
local_irq_save(flags);
completed_snap = ACCESS_ONCE(rsp->completed); /* outside of lock. */
/* Did another grace period end? */
if (rdp->completed != completed_snap) {
/* Advance callbacks. No harm if list empty. */
rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
/* Remember that we saw this grace-period completion. */
rdp->completed = completed_snap;
}
local_irq_restore(flags);
}
/*
* Similar to cpu_quiet(), for which it is a helper function. Allows
* a group of CPUs to be quieted at one go, though all the CPUs in the
* group must be represented by the same leaf rcu_node structure.
* That structure's lock must be held upon entry, and it is released
* before return.
*/
static void
cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp, struct rcu_node *rnp,
unsigned long flags)
__releases(rnp->lock)
{
/* Walk up the rcu_node hierarchy. */
for (;;) {
if (!(rnp->qsmask & mask)) {
/* Our bit has already been cleared, so done. */
spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
rnp->qsmask &= ~mask;
if (rnp->qsmask != 0) {
/* Other bits still set at this level, so done. */
spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
mask = rnp->grpmask;
if (rnp->parent == NULL) {
/* No more levels. Exit loop holding root lock. */
break;
}
spin_unlock_irqrestore(&rnp->lock, flags);
rnp = rnp->parent;
spin_lock_irqsave(&rnp->lock, flags);
}
/*
* Get here if we are the last CPU to pass through a quiescent
* state for this grace period. Clean up and let rcu_start_gp()
* start up the next grace period if one is needed. Note that
* we still hold rnp->lock, as required by rcu_start_gp(), which
* will release it.
*/
rsp->completed = rsp->gpnum;
rcu_process_gp_end(rsp, rsp->rda[smp_processor_id()]);
rcu_start_gp(rsp, flags); /* releases rnp->lock. */
}
/*
* Record a quiescent state for the specified CPU, which must either be
* the current CPU or an offline CPU. The lastcomp argument is used to
* make sure we are still in the grace period of interest. We don't want
* to end the current grace period based on quiescent states detected in
* an earlier grace period!
*/
static void
cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
{
unsigned long flags;
unsigned long mask;
struct rcu_node *rnp;
rnp = rdp->mynode;
spin_lock_irqsave(&rnp->lock, flags);
if (lastcomp != ACCESS_ONCE(rsp->completed)) {
/*
* Someone beat us to it for this grace period, so leave.
* The race with GP start is resolved by the fact that we
* hold the leaf rcu_node lock, so that the per-CPU bits
* cannot yet be initialized -- so we would simply find our
* CPU's bit already cleared in cpu_quiet_msk() if this race
* occurred.
*/
rdp->passed_quiesc = 0; /* try again later! */
spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
mask = rdp->grpmask;
if ((rnp->qsmask & mask) == 0) {
spin_unlock_irqrestore(&rnp->lock, flags);
} else {
rdp->qs_pending = 0;
/*
* This GP can't end until cpu checks in, so all of our
* callbacks can be processed during the next GP.
*/
rdp = rsp->rda[smp_processor_id()];
rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
cpu_quiet_msk(mask, rsp, rnp, flags); /* releases rnp->lock */
}
}
/*
* Check to see if there is a new grace period of which this CPU
* is not yet aware, and if so, set up local rcu_data state for it.
* Otherwise, see if this CPU has just passed through its first
* quiescent state for this grace period, and record that fact if so.
*/
static void
rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
{
/* If there is now a new grace period, record and return. */
if (check_for_new_grace_period(rsp, rdp))
return;
/*
* Does this CPU still need to do its part for current grace period?
* If no, return and let the other CPUs do their part as well.
*/
if (!rdp->qs_pending)
return;
/*
* Was there a quiescent state since the beginning of the grace
* period? If no, then exit and wait for the next call.
*/
if (!rdp->passed_quiesc)
return;
/* Tell RCU we are done (but cpu_quiet() will be the judge of that). */
cpu_quiet(rdp->cpu, rsp, rdp, rdp->passed_quiesc_completed);
}
#ifdef CONFIG_HOTPLUG_CPU
/*
* Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
* and move all callbacks from the outgoing CPU to the current one.
*/
static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
{
int i;
unsigned long flags;
long lastcomp;
unsigned long mask;
struct rcu_data *rdp = rsp->rda[cpu];
struct rcu_data *rdp_me;
struct rcu_node *rnp;
/* Exclude any attempts to start a new grace period. */
spin_lock_irqsave(&rsp->onofflock, flags);
/* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
rnp = rdp->mynode;
mask = rdp->grpmask; /* rnp->grplo is constant. */
do {
spin_lock(&rnp->lock); /* irqs already disabled. */
rnp->qsmaskinit &= ~mask;
if (rnp->qsmaskinit != 0) {
spin_unlock(&rnp->lock); /* irqs already disabled. */
break;
}
mask = rnp->grpmask;
spin_unlock(&rnp->lock); /* irqs already disabled. */
rnp = rnp->parent;
} while (rnp != NULL);
lastcomp = rsp->completed;
spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
/* Being offline is a quiescent state, so go record it. */
cpu_quiet(cpu, rsp, rdp, lastcomp);
/*
* Move callbacks from the outgoing CPU to the running CPU.
* Note that the outgoing CPU is now quiscent, so it is now
* (uncharacteristically) safe to access it rcu_data structure.
* Note also that we must carefully retain the order of the
* outgoing CPU's callbacks in order for rcu_barrier() to work
* correctly. Finally, note that we start all the callbacks
* afresh, even those that have passed through a grace period
* and are therefore ready to invoke. The theory is that hotplug
* events are rare, and that if they are frequent enough to
* indefinitely delay callbacks, you have far worse things to
* be worrying about.
*/
rdp_me = rsp->rda[smp_processor_id()];
if (rdp->nxtlist != NULL) {
*rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
rdp->nxtlist = NULL;
for (i = 0; i < RCU_NEXT_SIZE; i++)
rdp->nxttail[i] = &rdp->nxtlist;
rdp_me->qlen += rdp->qlen;
rdp->qlen = 0;
}
local_irq_restore(flags);
}
/*
* Remove the specified CPU from the RCU hierarchy and move any pending
* callbacks that it might have to the current CPU. This code assumes
* that at least one CPU in the system will remain running at all times.
* Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
*/
static void rcu_offline_cpu(int cpu)
{
__rcu_offline_cpu(cpu, &rcu_state);
__rcu_offline_cpu(cpu, &rcu_bh_state);
}
#else /* #ifdef CONFIG_HOTPLUG_CPU */
static void rcu_offline_cpu(int cpu)
{
}
#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
/*
* Invoke any RCU callbacks that have made it to the end of their grace
* period. Thottle as specified by rdp->blimit.
*/
static void rcu_do_batch(struct rcu_data *rdp)
{
unsigned long flags;
struct rcu_head *next, *list, **tail;
int count;
/* If no callbacks are ready, just return.*/
if (!cpu_has_callbacks_ready_to_invoke(rdp))
return;
/*
* Extract the list of ready callbacks, disabling to prevent
* races with call_rcu() from interrupt handlers.
*/
local_irq_save(flags);
list = rdp->nxtlist;
rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
*rdp->nxttail[RCU_DONE_TAIL] = NULL;
tail = rdp->nxttail[RCU_DONE_TAIL];
for (count = RCU_NEXT_SIZE - 1; count >= 0; count--)
if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL])
rdp->nxttail[count] = &rdp->nxtlist;
local_irq_restore(flags);
/* Invoke callbacks. */
count = 0;
while (list) {
next = list->next;
prefetch(next);
list->func(list);
list = next;
if (++count >= rdp->blimit)
break;
}
local_irq_save(flags);
/* Update count, and requeue any remaining callbacks. */
rdp->qlen -= count;
if (list != NULL) {
*tail = rdp->nxtlist;
rdp->nxtlist = list;
for (count = 0; count < RCU_NEXT_SIZE; count++)
if (&rdp->nxtlist == rdp->nxttail[count])
rdp->nxttail[count] = tail;
else
break;
}
/* Reinstate batch limit if we have worked down the excess. */
if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
rdp->blimit = blimit;
local_irq_restore(flags);
/* Re-raise the RCU softirq if there are callbacks remaining. */
if (cpu_has_callbacks_ready_to_invoke(rdp))
raise_softirq(RCU_SOFTIRQ);
}
/*
* Check to see if this CPU is in a non-context-switch quiescent state
* (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
* Also schedule the RCU softirq handler.
*
* This function must be called with hardirqs disabled. It is normally
* invoked from the scheduling-clock interrupt. If rcu_pending returns
* false, there is no point in invoking rcu_check_callbacks().
*/
void rcu_check_callbacks(int cpu, int user)
{
if (user ||
(idle_cpu(cpu) && !in_softirq() &&
hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
/*
* Get here if this CPU took its interrupt from user
* mode or from the idle loop, and if this is not a
* nested interrupt. In this case, the CPU is in
* a quiescent state, so count it.
*
* No memory barrier is required here because both
* rcu_qsctr_inc() and rcu_bh_qsctr_inc() reference
* only CPU-local variables that other CPUs neither
* access nor modify, at least not while the corresponding
* CPU is online.
*/
rcu_qsctr_inc(cpu);
rcu_bh_qsctr_inc(cpu);
} else if (!in_softirq()) {
/*
* Get here if this CPU did not take its interrupt from
* softirq, in other words, if it is not interrupting
* a rcu_bh read-side critical section. This is an _bh
* critical section, so count it.
*/
rcu_bh_qsctr_inc(cpu);
}
raise_softirq(RCU_SOFTIRQ);
}
#ifdef CONFIG_SMP
/*
* Scan the leaf rcu_node structures, processing dyntick state for any that
* have not yet encountered a quiescent state, using the function specified.
* Returns 1 if the current grace period ends while scanning (possibly
* because we made it end).
*/
static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
int (*f)(struct rcu_data *))
{
unsigned long bit;
int cpu;
unsigned long flags;
unsigned long mask;
struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];