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rcupreempt.c
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rcupreempt.c
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/*
* Read-Copy Update mechanism for mutual exclusion, realtime implementation
*
* 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, 2006
*
* Authors: Paul E. McKenney <[email protected]>
* With thanks to Esben Nielsen, Bill Huey, and Ingo Molnar
* for pushing me away from locks and towards counters, and
* to Suparna Bhattacharya for pushing me completely away
* from atomic instructions on the read side.
*
* - Added handling of Dynamic Ticks
* Copyright 2007 - Paul E. Mckenney <[email protected]>
* - Steven Rostedt <[email protected]>
*
* Papers: http://www.rdrop.com/users/paulmck/RCU
*
* Design Document: http://lwn.net/Articles/253651/
*
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU/ *.txt
*
*/
#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/kthread.h>
#include <linux/completion.h>
#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/random.h>
#include <linux/delay.h>
#include <linux/cpumask.h>
#include <linux/rcupreempt_trace.h>
#include <asm/byteorder.h>
/*
* PREEMPT_RCU data structures.
*/
/*
* GP_STAGES specifies the number of times the state machine has
* to go through the all the rcu_try_flip_states (see below)
* in a single Grace Period.
*
* GP in GP_STAGES stands for Grace Period ;)
*/
#define GP_STAGES 2
struct rcu_data {
spinlock_t lock; /* Protect rcu_data fields. */
long completed; /* Number of last completed batch. */
int waitlistcount;
struct rcu_head *nextlist;
struct rcu_head **nexttail;
struct rcu_head *waitlist[GP_STAGES];
struct rcu_head **waittail[GP_STAGES];
struct rcu_head *donelist; /* from waitlist & waitschedlist */
struct rcu_head **donetail;
long rcu_flipctr[2];
struct rcu_head *nextschedlist;
struct rcu_head **nextschedtail;
struct rcu_head *waitschedlist;
struct rcu_head **waitschedtail;
int rcu_sched_sleeping;
#ifdef CONFIG_RCU_TRACE
struct rcupreempt_trace trace;
#endif /* #ifdef CONFIG_RCU_TRACE */
};
/*
* States for rcu_try_flip() and friends.
*/
enum rcu_try_flip_states {
/*
* Stay here if nothing is happening. Flip the counter if somthing
* starts happening. Denoted by "I"
*/
rcu_try_flip_idle_state,
/*
* Wait here for all CPUs to notice that the counter has flipped. This
* prevents the old set of counters from ever being incremented once
* we leave this state, which in turn is necessary because we cannot
* test any individual counter for zero -- we can only check the sum.
* Denoted by "A".
*/
rcu_try_flip_waitack_state,
/*
* Wait here for the sum of the old per-CPU counters to reach zero.
* Denoted by "Z".
*/
rcu_try_flip_waitzero_state,
/*
* Wait here for each of the other CPUs to execute a memory barrier.
* This is necessary to ensure that these other CPUs really have
* completed executing their RCU read-side critical sections, despite
* their CPUs wildly reordering memory. Denoted by "M".
*/
rcu_try_flip_waitmb_state,
};
/*
* States for rcu_ctrlblk.rcu_sched_sleep.
*/
enum rcu_sched_sleep_states {
rcu_sched_not_sleeping, /* Not sleeping, callbacks need GP. */
rcu_sched_sleep_prep, /* Thinking of sleeping, rechecking. */
rcu_sched_sleeping, /* Sleeping, awaken if GP needed. */
};
struct rcu_ctrlblk {
spinlock_t fliplock; /* Protect state-machine transitions. */
long completed; /* Number of last completed batch. */
enum rcu_try_flip_states rcu_try_flip_state; /* The current state of
the rcu state machine */
spinlock_t schedlock; /* Protect rcu_sched sleep state. */
enum rcu_sched_sleep_states sched_sleep; /* rcu_sched state. */
wait_queue_head_t sched_wq; /* Place for rcu_sched to sleep. */
};
struct rcu_dyntick_sched {
int dynticks;
int dynticks_snap;
int sched_qs;
int sched_qs_snap;
int sched_dynticks_snap;
};
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_dyntick_sched, rcu_dyntick_sched) = {
.dynticks = 1,
};
void rcu_qsctr_inc(int cpu)
{
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
rdssp->sched_qs++;
}
#ifdef CONFIG_NO_HZ
void rcu_enter_nohz(void)
{
static DEFINE_RATELIMIT_STATE(rs, 10 * HZ, 1);
smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
__get_cpu_var(rcu_dyntick_sched).dynticks++;
WARN_ON_RATELIMIT(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1, &rs);
}
void rcu_exit_nohz(void)
{
static DEFINE_RATELIMIT_STATE(rs, 10 * HZ, 1);
__get_cpu_var(rcu_dyntick_sched).dynticks++;
smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
WARN_ON_RATELIMIT(!(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1),
&rs);
}
#endif /* CONFIG_NO_HZ */
static DEFINE_PER_CPU(struct rcu_data, rcu_data);
static struct rcu_ctrlblk rcu_ctrlblk = {
.fliplock = __SPIN_LOCK_UNLOCKED(rcu_ctrlblk.fliplock),
.completed = 0,
.rcu_try_flip_state = rcu_try_flip_idle_state,
.schedlock = __SPIN_LOCK_UNLOCKED(rcu_ctrlblk.schedlock),
.sched_sleep = rcu_sched_not_sleeping,
.sched_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rcu_ctrlblk.sched_wq),
};
static struct task_struct *rcu_sched_grace_period_task;
#ifdef CONFIG_RCU_TRACE
static char *rcu_try_flip_state_names[] =
{ "idle", "waitack", "waitzero", "waitmb" };
#endif /* #ifdef CONFIG_RCU_TRACE */
static DECLARE_BITMAP(rcu_cpu_online_map, NR_CPUS) __read_mostly
= CPU_BITS_NONE;
/*
* Enum and per-CPU flag to determine when each CPU has seen
* the most recent counter flip.
*/
enum rcu_flip_flag_values {
rcu_flip_seen, /* Steady/initial state, last flip seen. */
/* Only GP detector can update. */
rcu_flipped /* Flip just completed, need confirmation. */
/* Only corresponding CPU can update. */
};
static DEFINE_PER_CPU_SHARED_ALIGNED(enum rcu_flip_flag_values, rcu_flip_flag)
= rcu_flip_seen;
/*
* Enum and per-CPU flag to determine when each CPU has executed the
* needed memory barrier to fence in memory references from its last RCU
* read-side critical section in the just-completed grace period.
*/
enum rcu_mb_flag_values {
rcu_mb_done, /* Steady/initial state, no mb()s required. */
/* Only GP detector can update. */
rcu_mb_needed /* Flip just completed, need an mb(). */
/* Only corresponding CPU can update. */
};
static DEFINE_PER_CPU_SHARED_ALIGNED(enum rcu_mb_flag_values, rcu_mb_flag)
= rcu_mb_done;
/*
* RCU_DATA_ME: find the current CPU's rcu_data structure.
* RCU_DATA_CPU: find the specified CPU's rcu_data structure.
*/
#define RCU_DATA_ME() (&__get_cpu_var(rcu_data))
#define RCU_DATA_CPU(cpu) (&per_cpu(rcu_data, cpu))
/*
* Helper macro for tracing when the appropriate rcu_data is not
* cached in a local variable, but where the CPU number is so cached.
*/
#define RCU_TRACE_CPU(f, cpu) RCU_TRACE(f, &(RCU_DATA_CPU(cpu)->trace));
/*
* Helper macro for tracing when the appropriate rcu_data is not
* cached in a local variable.
*/
#define RCU_TRACE_ME(f) RCU_TRACE(f, &(RCU_DATA_ME()->trace));
/*
* Helper macro for tracing when the appropriate rcu_data is pointed
* to by a local variable.
*/
#define RCU_TRACE_RDP(f, rdp) RCU_TRACE(f, &((rdp)->trace));
#define RCU_SCHED_BATCH_TIME (HZ / 50)
/*
* Return the number of RCU batches processed thus far. Useful
* for debug and statistics.
*/
long rcu_batches_completed(void)
{
return rcu_ctrlblk.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);
void __rcu_read_lock(void)
{
int idx;
struct task_struct *t = current;
int nesting;
nesting = ACCESS_ONCE(t->rcu_read_lock_nesting);
if (nesting != 0) {
/* An earlier rcu_read_lock() covers us, just count it. */
t->rcu_read_lock_nesting = nesting + 1;
} else {
unsigned long flags;
/*
* We disable interrupts for the following reasons:
* - If we get scheduling clock interrupt here, and we
* end up acking the counter flip, it's like a promise
* that we will never increment the old counter again.
* Thus we will break that promise if that
* scheduling clock interrupt happens between the time
* we pick the .completed field and the time that we
* increment our counter.
*
* - We don't want to be preempted out here.
*
* NMIs can still occur, of course, and might themselves
* contain rcu_read_lock().
*/
local_irq_save(flags);
/*
* Outermost nesting of rcu_read_lock(), so increment
* the current counter for the current CPU. Use volatile
* casts to prevent the compiler from reordering.
*/
idx = ACCESS_ONCE(rcu_ctrlblk.completed) & 0x1;
ACCESS_ONCE(RCU_DATA_ME()->rcu_flipctr[idx])++;
/*
* Now that the per-CPU counter has been incremented, we
* are protected from races with rcu_read_lock() invoked
* from NMI handlers on this CPU. We can therefore safely
* increment the nesting counter, relieving further NMIs
* of the need to increment the per-CPU counter.
*/
ACCESS_ONCE(t->rcu_read_lock_nesting) = nesting + 1;
/*
* Now that we have preventing any NMIs from storing
* to the ->rcu_flipctr_idx, we can safely use it to
* remember which counter to decrement in the matching
* rcu_read_unlock().
*/
ACCESS_ONCE(t->rcu_flipctr_idx) = idx;
local_irq_restore(flags);
}
}
EXPORT_SYMBOL_GPL(__rcu_read_lock);
void __rcu_read_unlock(void)
{
int idx;
struct task_struct *t = current;
int nesting;
nesting = ACCESS_ONCE(t->rcu_read_lock_nesting);
if (nesting > 1) {
/*
* We are still protected by the enclosing rcu_read_lock(),
* so simply decrement the counter.
*/
t->rcu_read_lock_nesting = nesting - 1;
} else {
unsigned long flags;
/*
* Disable local interrupts to prevent the grace-period
* detection state machine from seeing us half-done.
* NMIs can still occur, of course, and might themselves
* contain rcu_read_lock() and rcu_read_unlock().
*/
local_irq_save(flags);
/*
* Outermost nesting of rcu_read_unlock(), so we must
* decrement the current counter for the current CPU.
* This must be done carefully, because NMIs can
* occur at any point in this code, and any rcu_read_lock()
* and rcu_read_unlock() pairs in the NMI handlers
* must interact non-destructively with this code.
* Lots of volatile casts, and -very- careful ordering.
*
* Changes to this code, including this one, must be
* inspected, validated, and tested extremely carefully!!!
*/
/*
* First, pick up the index.
*/
idx = ACCESS_ONCE(t->rcu_flipctr_idx);
/*
* Now that we have fetched the counter index, it is
* safe to decrement the per-task RCU nesting counter.
* After this, any interrupts or NMIs will increment and
* decrement the per-CPU counters.
*/
ACCESS_ONCE(t->rcu_read_lock_nesting) = nesting - 1;
/*
* It is now safe to decrement this task's nesting count.
* NMIs that occur after this statement will route their
* rcu_read_lock() calls through this "else" clause, and
* will thus start incrementing the per-CPU counter on
* their own. They will also clobber ->rcu_flipctr_idx,
* but that is OK, since we have already fetched it.
*/
ACCESS_ONCE(RCU_DATA_ME()->rcu_flipctr[idx])--;
local_irq_restore(flags);
}
}
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
/*
* If a global counter flip has occurred since the last time that we
* advanced callbacks, advance them. Hardware interrupts must be
* disabled when calling this function.
*/
static void __rcu_advance_callbacks(struct rcu_data *rdp)
{
int cpu;
int i;
int wlc = 0;
if (rdp->completed != rcu_ctrlblk.completed) {
if (rdp->waitlist[GP_STAGES - 1] != NULL) {
*rdp->donetail = rdp->waitlist[GP_STAGES - 1];
rdp->donetail = rdp->waittail[GP_STAGES - 1];
RCU_TRACE_RDP(rcupreempt_trace_move2done, rdp);
}
for (i = GP_STAGES - 2; i >= 0; i--) {
if (rdp->waitlist[i] != NULL) {
rdp->waitlist[i + 1] = rdp->waitlist[i];
rdp->waittail[i + 1] = rdp->waittail[i];
wlc++;
} else {
rdp->waitlist[i + 1] = NULL;
rdp->waittail[i + 1] =
&rdp->waitlist[i + 1];
}
}
if (rdp->nextlist != NULL) {
rdp->waitlist[0] = rdp->nextlist;
rdp->waittail[0] = rdp->nexttail;
wlc++;
rdp->nextlist = NULL;
rdp->nexttail = &rdp->nextlist;
RCU_TRACE_RDP(rcupreempt_trace_move2wait, rdp);
} else {
rdp->waitlist[0] = NULL;
rdp->waittail[0] = &rdp->waitlist[0];
}
rdp->waitlistcount = wlc;
rdp->completed = rcu_ctrlblk.completed;
}
/*
* Check to see if this CPU needs to report that it has seen
* the most recent counter flip, thereby declaring that all
* subsequent rcu_read_lock() invocations will respect this flip.
*/
cpu = raw_smp_processor_id();
if (per_cpu(rcu_flip_flag, cpu) == rcu_flipped) {
smp_mb(); /* Subsequent counter accesses must see new value */
per_cpu(rcu_flip_flag, cpu) = rcu_flip_seen;
smp_mb(); /* Subsequent RCU read-side critical sections */
/* seen -after- acknowledgement. */
}
}
#ifdef CONFIG_NO_HZ
static DEFINE_PER_CPU(int, rcu_update_flag);
/**
* rcu_irq_enter - Called from Hard irq handlers and NMI/SMI.
*
* If the CPU was idle with dynamic ticks active, this updates the
* rcu_dyntick_sched.dynticks to let the RCU handling know that the
* CPU is active.
*/
void rcu_irq_enter(void)
{
int cpu = smp_processor_id();
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
if (per_cpu(rcu_update_flag, cpu))
per_cpu(rcu_update_flag, cpu)++;
/*
* Only update if we are coming from a stopped ticks mode
* (rcu_dyntick_sched.dynticks is even).
*/
if (!in_interrupt() &&
(rdssp->dynticks & 0x1) == 0) {
/*
* The following might seem like we could have a race
* with NMI/SMIs. But this really isn't a problem.
* Here we do a read/modify/write, and the race happens
* when an NMI/SMI comes in after the read and before
* the write. But NMI/SMIs will increment this counter
* twice before returning, so the zero bit will not
* be corrupted by the NMI/SMI which is the most important
* part.
*
* The only thing is that we would bring back the counter
* to a postion that it was in during the NMI/SMI.
* But the zero bit would be set, so the rest of the
* counter would again be ignored.
*
* On return from the IRQ, the counter may have the zero
* bit be 0 and the counter the same as the return from
* the NMI/SMI. If the state machine was so unlucky to
* see that, it still doesn't matter, since all
* RCU read-side critical sections on this CPU would
* have already completed.
*/
rdssp->dynticks++;
/*
* The following memory barrier ensures that any
* rcu_read_lock() primitives in the irq handler
* are seen by other CPUs to follow the above
* increment to rcu_dyntick_sched.dynticks. This is
* required in order for other CPUs to correctly
* determine when it is safe to advance the RCU
* grace-period state machine.
*/
smp_mb(); /* see above block comment. */
/*
* Since we can't determine the dynamic tick mode from
* the rcu_dyntick_sched.dynticks after this routine,
* we use a second flag to acknowledge that we came
* from an idle state with ticks stopped.
*/
per_cpu(rcu_update_flag, cpu)++;
/*
* If we take an NMI/SMI now, they will also increment
* the rcu_update_flag, and will not update the
* rcu_dyntick_sched.dynticks on exit. That is for
* this IRQ to do.
*/
}
}
/**
* rcu_irq_exit - Called from exiting Hard irq context.
*
* If the CPU was idle with dynamic ticks active, update the
* rcu_dyntick_sched.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)
{
int cpu = smp_processor_id();
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
/*
* rcu_update_flag is set if we interrupted the CPU
* when it was idle with ticks stopped.
* Once this occurs, we keep track of interrupt nesting
* because a NMI/SMI could also come in, and we still
* only want the IRQ that started the increment of the
* rcu_dyntick_sched.dynticks to be the one that modifies
* it on exit.
*/
if (per_cpu(rcu_update_flag, cpu)) {
if (--per_cpu(rcu_update_flag, cpu))
return;
/* This must match the interrupt nesting */
WARN_ON(in_interrupt());
/*
* If an NMI/SMI happens now we are still
* protected by the rcu_dyntick_sched.dynticks being odd.
*/
/*
* The following memory barrier ensures that any
* rcu_read_unlock() primitives in the irq handler
* are seen by other CPUs to preceed the following
* increment to rcu_dyntick_sched.dynticks. This
* is required in order for other CPUs to determine
* when it is safe to advance the RCU grace-period
* state machine.
*/
smp_mb(); /* see above block comment. */
rdssp->dynticks++;
WARN_ON(rdssp->dynticks & 0x1);
}
}
void rcu_nmi_enter(void)
{
rcu_irq_enter();
}
void rcu_nmi_exit(void)
{
rcu_irq_exit();
}
static void dyntick_save_progress_counter(int cpu)
{
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
rdssp->dynticks_snap = rdssp->dynticks;
}
static inline int
rcu_try_flip_waitack_needed(int cpu)
{
long curr;
long snap;
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
curr = rdssp->dynticks;
snap = rdssp->dynticks_snap;
smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
/*
* If the CPU remained in dynticks mode for the entire time
* and didn't take any interrupts, NMIs, SMIs, or whatever,
* then it cannot be in the middle of an rcu_read_lock(), so
* the next rcu_read_lock() it executes must use the new value
* of the counter. So we can safely pretend that this CPU
* already acknowledged the counter.
*/
if ((curr == snap) && ((curr & 0x1) == 0))
return 0;
/*
* If the CPU passed through or entered a dynticks idle phase with
* no active irq handlers, then, as above, we can safely pretend
* that this CPU already acknowledged the counter.
*/
if ((curr - snap) > 2 || (curr & 0x1) == 0)
return 0;
/* We need this CPU to explicitly acknowledge the counter flip. */
return 1;
}
static inline int
rcu_try_flip_waitmb_needed(int cpu)
{
long curr;
long snap;
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
curr = rdssp->dynticks;
snap = rdssp->dynticks_snap;
smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
/*
* If the CPU remained in dynticks mode for the entire time
* and didn't take any interrupts, NMIs, SMIs, or whatever,
* then it cannot have executed an RCU read-side critical section
* during that time, so there is no need for it to execute a
* memory barrier.
*/
if ((curr == snap) && ((curr & 0x1) == 0))
return 0;
/*
* If the CPU either entered or exited an outermost interrupt,
* SMI, NMI, or whatever handler, then we know that it executed
* a memory barrier when doing so. So we don't need another one.
*/
if (curr != snap)
return 0;
/* We need the CPU to execute a memory barrier. */
return 1;
}
static void dyntick_save_progress_counter_sched(int cpu)
{
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
rdssp->sched_dynticks_snap = rdssp->dynticks;
}
static int rcu_qsctr_inc_needed_dyntick(int cpu)
{
long curr;
long snap;
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
curr = rdssp->dynticks;
snap = rdssp->sched_dynticks_snap;
smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
/*
* If the CPU remained in dynticks mode for the entire time
* and didn't take any interrupts, NMIs, SMIs, or whatever,
* then it cannot be in the middle of an rcu_read_lock(), so
* the next rcu_read_lock() it executes must use the new value
* of the counter. Therefore, this CPU has been in a quiescent
* state the entire time, and we don't need to wait for it.
*/
if ((curr == snap) && ((curr & 0x1) == 0))
return 0;
/*
* If the CPU passed through or entered a dynticks idle phase with
* no active irq handlers, then, as above, this CPU has already
* passed through a quiescent state.
*/
if ((curr - snap) > 2 || (snap & 0x1) == 0)
return 0;
/* We need this CPU to go through a quiescent state. */
return 1;
}
#else /* !CONFIG_NO_HZ */
# define dyntick_save_progress_counter(cpu) do { } while (0)
# define rcu_try_flip_waitack_needed(cpu) (1)
# define rcu_try_flip_waitmb_needed(cpu) (1)
# define dyntick_save_progress_counter_sched(cpu) do { } while (0)
# define rcu_qsctr_inc_needed_dyntick(cpu) (1)
#endif /* CONFIG_NO_HZ */
static void save_qsctr_sched(int cpu)
{
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
rdssp->sched_qs_snap = rdssp->sched_qs;
}
static inline int rcu_qsctr_inc_needed(int cpu)
{
struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
/*
* If there has been a quiescent state, no more need to wait
* on this CPU.
*/
if (rdssp->sched_qs != rdssp->sched_qs_snap) {
smp_mb(); /* force ordering with cpu entering schedule(). */
return 0;
}
/* We need this CPU to go through a quiescent state. */
return 1;
}
/*
* Get here when RCU is idle. Decide whether we need to
* move out of idle state, and return non-zero if so.
* "Straightforward" approach for the moment, might later
* use callback-list lengths, grace-period duration, or
* some such to determine when to exit idle state.
* Might also need a pre-idle test that does not acquire
* the lock, but let's get the simple case working first...
*/
static int
rcu_try_flip_idle(void)
{
int cpu;
RCU_TRACE_ME(rcupreempt_trace_try_flip_i1);
if (!rcu_pending(smp_processor_id())) {
RCU_TRACE_ME(rcupreempt_trace_try_flip_ie1);
return 0;
}
/*
* Do the flip.
*/
RCU_TRACE_ME(rcupreempt_trace_try_flip_g1);
rcu_ctrlblk.completed++; /* stands in for rcu_try_flip_g2 */
/*
* Need a memory barrier so that other CPUs see the new
* counter value before they see the subsequent change of all
* the rcu_flip_flag instances to rcu_flipped.
*/
smp_mb(); /* see above block comment. */
/* Now ask each CPU for acknowledgement of the flip. */
for_each_cpu(cpu, to_cpumask(rcu_cpu_online_map)) {
per_cpu(rcu_flip_flag, cpu) = rcu_flipped;
dyntick_save_progress_counter(cpu);
}
return 1;
}
/*
* Wait for CPUs to acknowledge the flip.
*/
static int
rcu_try_flip_waitack(void)
{
int cpu;
RCU_TRACE_ME(rcupreempt_trace_try_flip_a1);
for_each_cpu(cpu, to_cpumask(rcu_cpu_online_map))
if (rcu_try_flip_waitack_needed(cpu) &&
per_cpu(rcu_flip_flag, cpu) != rcu_flip_seen) {
RCU_TRACE_ME(rcupreempt_trace_try_flip_ae1);
return 0;
}
/*
* Make sure our checks above don't bleed into subsequent
* waiting for the sum of the counters to reach zero.
*/
smp_mb(); /* see above block comment. */
RCU_TRACE_ME(rcupreempt_trace_try_flip_a2);
return 1;
}
/*
* Wait for collective ``last'' counter to reach zero,
* then tell all CPUs to do an end-of-grace-period memory barrier.
*/
static int
rcu_try_flip_waitzero(void)
{
int cpu;
int lastidx = !(rcu_ctrlblk.completed & 0x1);
int sum = 0;
/* Check to see if the sum of the "last" counters is zero. */
RCU_TRACE_ME(rcupreempt_trace_try_flip_z1);
for_each_cpu(cpu, to_cpumask(rcu_cpu_online_map))
sum += RCU_DATA_CPU(cpu)->rcu_flipctr[lastidx];
if (sum != 0) {
RCU_TRACE_ME(rcupreempt_trace_try_flip_ze1);
return 0;
}
/*
* This ensures that the other CPUs see the call for
* memory barriers -after- the sum to zero has been
* detected here
*/
smp_mb(); /* ^^^^^^^^^^^^ */
/* Call for a memory barrier from each CPU. */
for_each_cpu(cpu, to_cpumask(rcu_cpu_online_map)) {
per_cpu(rcu_mb_flag, cpu) = rcu_mb_needed;
dyntick_save_progress_counter(cpu);
}
RCU_TRACE_ME(rcupreempt_trace_try_flip_z2);
return 1;
}
/*
* Wait for all CPUs to do their end-of-grace-period memory barrier.
* Return 0 once all CPUs have done so.
*/
static int
rcu_try_flip_waitmb(void)
{
int cpu;
RCU_TRACE_ME(rcupreempt_trace_try_flip_m1);
for_each_cpu(cpu, to_cpumask(rcu_cpu_online_map))
if (rcu_try_flip_waitmb_needed(cpu) &&
per_cpu(rcu_mb_flag, cpu) != rcu_mb_done) {
RCU_TRACE_ME(rcupreempt_trace_try_flip_me1);
return 0;
}
smp_mb(); /* Ensure that the above checks precede any following flip. */
RCU_TRACE_ME(rcupreempt_trace_try_flip_m2);
return 1;
}
/*
* Attempt a single flip of the counters. Remember, a single flip does
* -not- constitute a grace period. Instead, the interval between
* at least GP_STAGES consecutive flips is a grace period.
*
* If anyone is nuts enough to run this CONFIG_PREEMPT_RCU implementation
* on a large SMP, they might want to use a hierarchical organization of
* the per-CPU-counter pairs.
*/
static void rcu_try_flip(void)
{
unsigned long flags;
RCU_TRACE_ME(rcupreempt_trace_try_flip_1);
if (unlikely(!spin_trylock_irqsave(&rcu_ctrlblk.fliplock, flags))) {
RCU_TRACE_ME(rcupreempt_trace_try_flip_e1);
return;
}
/*
* Take the next transition(s) through the RCU grace-period
* flip-counter state machine.
*/
switch (rcu_ctrlblk.rcu_try_flip_state) {
case rcu_try_flip_idle_state:
if (rcu_try_flip_idle())
rcu_ctrlblk.rcu_try_flip_state =
rcu_try_flip_waitack_state;
break;
case rcu_try_flip_waitack_state:
if (rcu_try_flip_waitack())
rcu_ctrlblk.rcu_try_flip_state =
rcu_try_flip_waitzero_state;
break;
case rcu_try_flip_waitzero_state:
if (rcu_try_flip_waitzero())
rcu_ctrlblk.rcu_try_flip_state =
rcu_try_flip_waitmb_state;
break;
case rcu_try_flip_waitmb_state:
if (rcu_try_flip_waitmb())
rcu_ctrlblk.rcu_try_flip_state =
rcu_try_flip_idle_state;
}
spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
}
/*
* Check to see if this CPU needs to do a memory barrier in order to
* ensure that any prior RCU read-side critical sections have committed
* their counter manipulations and critical-section memory references
* before declaring the grace period to be completed.
*/
static void rcu_check_mb(int cpu)
{
if (per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed) {
smp_mb(); /* Ensure RCU read-side accesses are visible. */
per_cpu(rcu_mb_flag, cpu) = rcu_mb_done;
}
}
void rcu_check_callbacks(int cpu, int user)
{
unsigned long flags;
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
/*
* If this CPU took its interrupt from user mode or from the
* idle loop, and this is not a nested interrupt, then
* this CPU has to have exited all prior preept-disable
* sections of code. So increment the counter to note this.
*
* The memory barrier is needed to handle the case where
* writes from a preempt-disable section of code get reordered
* into schedule() by this CPU's write buffer. So the memory
* barrier makes sure that the rcu_qsctr_inc() is seen by other
* CPUs to happen after any such write.
*/
if (user ||
(idle_cpu(cpu) && !in_softirq() &&
hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
smp_mb(); /* Guard against aggressive schedule(). */
rcu_qsctr_inc(cpu);
}
rcu_check_mb(cpu);
if (rcu_ctrlblk.completed == rdp->completed)
rcu_try_flip();
spin_lock_irqsave(&rdp->lock, flags);
RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp);
__rcu_advance_callbacks(rdp);
if (rdp->donelist == NULL) {
spin_unlock_irqrestore(&rdp->lock, flags);
} else {
spin_unlock_irqrestore(&rdp->lock, flags);
raise_softirq(RCU_SOFTIRQ);
}
}
/*