rcu: Remove CONFIG_PREEMPT_RCU

Now that CONFIG_TREE_PREEMPT_RCU is in place, there is no
further need for CONFIG_PREEMPT_RCU.  Remove it, along with
whatever subtle bugs it may (or may not) contain.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josht@linux.vnet.ibm.com
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
LKML-Reference: <125097461396-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 0 insertions, 1518 deletions

diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
deleted file mode 100644
index 0053ce56e326..000000000000
--- a/kernel/rcupreempt.c
+++ /dev/null
@@ -1,1518 +0,0 @@
-/*
- * 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 <paulmck@us.ibm.com>
- *              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 <paulmck@us.ibm.com>
- *                     - Steven Rostedt <srostedt@redhat.com>
- *
- * 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,
-};
-
-static int rcu_pending(int cpu);
-
-void rcu_sched_qs(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 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_possible_cpu(cpu)
-                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;
-
-        if (!rcu_pending(cpu))
-                return; /* if nothing for RCU to do. */
-
-        /*
-         * 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 invoke rcu_sched_qs() 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_sched_qs() is seen by other
-         * CPUs to happen after any such write.
-         */
-
-        rdp = RCU_DATA_CPU(cpu);
-        if (user ||
-            (idle_cpu(cpu) && !in_softirq() &&
-             hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
-                smp_mb();       /* Guard against aggressive schedule(). */
-                rcu_sched_qs(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);
-        }
-}
-
-/*
- * Needed by dynticks, to make sure all RCU processing has finished
- * when we go idle:
- */
-void rcu_advance_callbacks(int cpu, int user)
-{
-        unsigned long flags;
-        struct rcu_data *rdp = RCU_DATA_CPU(cpu);
-
-        if (rcu_ctrlblk.completed == rdp->completed) {
-                rcu_try_flip();
-                if (rcu_ctrlblk.completed == rdp->completed)
-                        return;
-        }
-        spin_lock_irqsave(&rdp->lock, flags);
-        RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp);
-        __rcu_advance_callbacks(rdp);
-        spin_unlock_irqrestore(&rdp->lock, flags);
-}
-
-#ifdef CONFIG_HOTPLUG_CPU
-#define rcu_offline_cpu_enqueue(srclist, srctail, dstlist, dsttail) do { \
-                *dsttail = srclist; \
-                if (srclist != NULL) { \
-                        dsttail = srctail; \
-                        srclist = NULL; \
-                        srctail = &srclist;\
-                } \
-        } while (0)
-
-void rcu_offline_cpu(int cpu)
-{
-        int i;
-        struct rcu_head *list = NULL;
-        unsigned long flags;
-        struct rcu_data *rdp = RCU_DATA_CPU(cpu);
-        struct rcu_head *schedlist = NULL;
-        struct rcu_head **schedtail = &schedlist;
-        struct rcu_head **tail = &list;
-
-        /*
-         * Remove all callbacks from the newly dead CPU, retaining order.
-         * Otherwise rcu_barrier() will fail
-         */
-
-        spin_lock_irqsave(&rdp->lock, flags);
-        rcu_offline_cpu_enqueue(rdp->donelist, rdp->donetail, list, tail);
-        for (i = GP_STAGES - 1; i >= 0; i--)
-                rcu_offline_cpu_enqueue(rdp->waitlist[i], rdp->waittail[i],
-                                                list, tail);
-        rcu_offline_cpu_enqueue(rdp->nextlist, rdp->nexttail, list, tail);
-        rcu_offline_cpu_enqueue(rdp->waitschedlist, rdp->waitschedtail,
-                                schedlist, schedtail);
-        rcu_offline_cpu_enqueue(rdp->nextschedlist, rdp->nextschedtail,
-                                schedlist, schedtail);
-        rdp->rcu_sched_sleeping = 0;
-        spin_unlock_irqrestore(&rdp->lock, flags);
-        rdp->waitlistcount = 0;
-
-        /* Disengage the newly dead CPU from the grace-period computation. */
-
-        spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
-        rcu_check_mb(cpu);
-        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. */
-        }
-
-        cpumask_clear_cpu(cpu, to_cpumask(rcu_cpu_online_map));
-
-        spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
-
-        /*
-         * Place the removed callbacks on the current CPU's queue.
-         * Make them all start a new grace period: simple approach,
-         * in theory could starve a given set of callbacks, but
-         * you would need to be doing some serious CPU hotplugging
-         * to make this happen.  If this becomes a problem, adding
-         * a synchronize_rcu() to the hotplug path would be a simple
-         * fix.
-         */
-
-        local_irq_save(flags);  /* disable preempt till we know what lock. */
-        rdp = RCU_DATA_ME();
-        spin_lock(&rdp->lock);
-        *rdp->nexttail = list;
-        if (list)
-                rdp->nexttail = tail;
-        *rdp->nextschedtail = schedlist;
-        if (schedlist)
-                rdp->nextschedtail = schedtail;
-        spin_unlock_irqrestore(&rdp->lock, flags);
-}
-
-#else /* #ifdef CONFIG_HOTPLUG_CPU */
-
-void rcu_offline_cpu(int cpu)
-{
-}
-
-#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
-
-void __cpuinit rcu_online_cpu(int cpu)
-{
-        unsigned long flags;
-        struct rcu_data *rdp;
-
-        spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
-        cpumask_set_cpu(cpu, to_cpumask(rcu_cpu_online_map));
-        spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
-
-        /*
-         * The rcu_sched grace-period processing might have bypassed
-         * this CPU, given that it was not in the rcu_cpu_online_map
-         * when the grace-period scan started.  This means that the
-         * grace-period task might sleep.  So make sure that if this
-         * should happen, the first callback posted to this CPU will
-         * wake up the grace-period task if need be.
-         */
-
-        rdp = RCU_DATA_CPU(cpu);
-        spin_lock_irqsave(&rdp->lock, flags);
-        rdp->rcu_sched_sleeping = 1;
-        spin_unlock_irqrestore(&rdp->lock, flags);
-}
-
-static void rcu_process_callbacks(struct softirq_action *unused)
-{
-        unsigned long flags;
-        struct rcu_head *next, *list;
-        struct rcu_data *rdp;
-
-        local_irq_save(flags);
-        rdp = RCU_DATA_ME();
-        spin_lock(&rdp->lock);
-        list = rdp->donelist;
-        if (list == NULL) {
-                spin_unlock_irqrestore(&rdp->lock, flags);
-                return;
-        }
-        rdp->donelist = NULL;
-        rdp->donetail = &rdp->donelist;
-        RCU_TRACE_RDP(rcupreempt_trace_done_remove, rdp);
-        spin_unlock_irqrestore(&rdp->lock, flags);
-        while (list) {
-                next = list->next;
-                list->func(list);
-                list = next;
-                RCU_TRACE_ME(rcupreempt_trace_invoke);
-        }
-}
-
-void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
-{
-        unsigned long flags;
-        struct rcu_data *rdp;
-
-        head->func = func;
-        head->next = NULL;
-        local_irq_save(flags);
-        rdp = RCU_DATA_ME();
-        spin_lock(&rdp->lock);
-        __rcu_advance_callbacks(rdp);
-        *rdp->nexttail = head;
-        rdp->nexttail = &head->next;
-        RCU_TRACE_RDP(rcupreempt_trace_next_add, rdp);
-        spin_unlock_irqrestore(&rdp->lock, flags);
-}
-EXPORT_SYMBOL_GPL(call_rcu);
-
-void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
-{
-        unsigned long flags;
-        struct rcu_data *rdp;
-        int wake_gp = 0;
-
-        head->func = func;
-        head->next = NULL;
-        local_irq_save(flags);
-        rdp = RCU_DATA_ME();
-        spin_lock(&rdp->lock);
-        *rdp->nextschedtail = head;
-        rdp->nextschedtail = &head->next;
-        if (rdp->rcu_sched_sleeping) {
-
-                /* Grace-period processing might be sleeping... */
-
-                rdp->rcu_sched_sleeping = 0;
-                wake_gp = 1;
-        }
-        spin_unlock_irqrestore(&rdp->lock, flags);
-        if (wake_gp) {
-
-                /* Wake up grace-period processing, unless someone beat us. */
-
-                spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
-                if (rcu_ctrlblk.sched_sleep != rcu_sched_sleeping)
-                        wake_gp = 0;
-                rcu_ctrlblk.sched_sleep = rcu_sched_not_sleeping;
-                spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
-                if (wake_gp)
-                        wake_up_interruptible(&rcu_ctrlblk.sched_wq);
-        }
-}
-EXPORT_SYMBOL_GPL(call_rcu_sched);
-
-/*
- * Wait until all currently running preempt_disable() code segments
- * (including hardware-irq-disable segments) complete.  Note that
- * in -rt this does -not- necessarily result in all currently executing
- * interrupt -handlers- having completed.
- */
-void __synchronize_sched(void)
-{
-        struct rcu_synchronize rcu;
-
-        if (num_online_cpus() == 1)
-                return;  /* blocking is gp if only one CPU! */
-
-        init_completion(&rcu.completion);
-        /* Will wake me after RCU finished. */
-        call_rcu_sched(&rcu.head, wakeme_after_rcu);
-        /* Wait for it. */
-        wait_for_completion(&rcu.completion);
-}
-EXPORT_SYMBOL_GPL(__synchronize_sched);
-
-/*
- * kthread function that manages call_rcu_sched grace periods.
- */
-static int rcu_sched_grace_period(void *arg)
-{
-        int couldsleep;         /* might sleep after current pass. */
-        int couldsleepnext = 0; /* might sleep after next pass. */
-        int cpu;
-        unsigned long flags;
-        struct rcu_data *rdp;
-        int ret;
-
-        /*
-         * Each pass through the following loop handles one
-         * rcu_sched grace period cycle.
-         */
-        do {
-                /* Save each CPU's current state. */
-
-                for_each_online_cpu(cpu) {
-                        dyntick_save_progress_counter_sched(cpu);
-                        save_qsctr_sched(cpu);
-                }
-
-                /*
-                 * Sleep for about an RCU grace-period's worth to
-                 * allow better batching and to consume less CPU.
-                 */
-                schedule_timeout_interruptible(RCU_SCHED_BATCH_TIME);
-
-                /*
-                 * If there was nothing to do last time, prepare to
-                 * sleep at the end of the current grace period cycle.
-                 */
-                couldsleep = couldsleepnext;
-                couldsleepnext = 1;
-                if (couldsleep) {
-                        spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
-                        rcu_ctrlblk.sched_sleep = rcu_sched_sleep_prep;
-                        spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
-                }
-
-                /*
-                 * Wait on each CPU in turn to have either visited
-                 * a quiescent state or been in dynticks-idle mode.
-                 */
-                for_each_online_cpu(cpu) {
-                        while (rcu_qsctr_inc_needed(cpu) &&
-                               rcu_qsctr_inc_needed_dyntick(cpu)) {
-                                /* resched_cpu(cpu); @@@ */
-                                schedule_timeout_interruptible(1);
-                        }
-                }
-
-                /* Advance callbacks for each CPU.  */
-
-                for_each_online_cpu(cpu) {
-
-                        rdp = RCU_DATA_CPU(cpu);
-                        spin_lock_irqsave(&rdp->lock, flags);
-
-                        /*
-                         * We are running on this CPU irq-disabled, so no
-                         * CPU can go offline until we re-enable irqs.
-                         * The current CPU might have already gone
-                         * offline (between the for_each_offline_cpu and
-                         * the spin_lock_irqsave), but in that case all its
-                         * callback lists will be empty, so no harm done.
-                         *
-                         * Advance the callbacks!  We share normal RCU's
-                         * donelist, since callbacks are invoked the
-                         * same way in either case.
-                         */
-                        if (rdp->waitschedlist != NULL) {
-                                *rdp->donetail = rdp->waitschedlist;
-                                rdp->donetail = rdp->waitschedtail;
-
-                                /*
-                                 * Next rcu_check_callbacks() will
-                                 * do the required raise_softirq().
-                                 */
-                        }
-                        if (rdp->nextschedlist != NULL) {
-                                rdp->waitschedlist = rdp->nextschedlist;
-                                rdp->waitschedtail = rdp->nextschedtail;
-                                couldsleep = 0;
-                                couldsleepnext = 0;
-                        } else {
-                                rdp->waitschedlist = NULL;
-                                rdp->waitschedtail = &rdp->waitschedlist;
-                        }
-                        rdp->nextschedlist = NULL;
-                        rdp->nextschedtail = &rdp->nextschedlist;
-
-                        /* Mark sleep intention. */
-
-                        rdp->rcu_sched_sleeping = couldsleep;
-
-                        spin_unlock_irqrestore(&rdp->lock, flags);
-                }
-
-                /* If we saw callbacks on the last scan, go deal with them. */
-
-                if (!couldsleep)
-                        continue;
-
-                /* Attempt to block... */
-
-                spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
-                if (rcu_ctrlblk.sched_sleep != rcu_sched_sleep_prep) {
-
-                        /*
-                         * Someone posted a callback after we scanned.
-                         * Go take care of it.
-                         */
-                        spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
-                        couldsleepnext = 0;
-                        continue;
-                }
-
-                /* Block until the next person posts a callback. */
-
-                rcu_ctrlblk.sched_sleep = rcu_sched_sleeping;
-                spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
-                ret = 0; /* unused */
-                __wait_event_interruptible(rcu_ctrlblk.sched_wq,
-                        rcu_ctrlblk.sched_sleep != rcu_sched_sleeping,
-                        ret);
-
-                couldsleepnext = 0;
-
-        } while (!kthread_should_stop());
-
-        return (0);
-}
-
-/*
- * Check to see if any future RCU-related work will need to be done
- * by the current CPU, even if none need be done immediately, returning
- * 1 if so.  Assumes that notifiers would take care of handling any
- * outstanding requests from the RCU core.
- *
- * This function is part of the RCU implementation; it is -not-
- * an exported member of the RCU API.
- */
-int rcu_needs_cpu(int cpu)
-{
-        struct rcu_data *rdp = RCU_DATA_CPU(cpu);
-
-        return (rdp->donelist != NULL ||
-                !!rdp->waitlistcount ||
-                rdp->nextlist != NULL ||
-                rdp->nextschedlist != NULL ||
-                rdp->waitschedlist != NULL);
-}
-
-static int rcu_pending(int cpu)
-{
-        struct rcu_data *rdp = RCU_DATA_CPU(cpu);
-
-        /* The CPU has at least one callback queued somewhere. */
-
-        if (rdp->donelist != NULL ||
-            !!rdp->waitlistcount ||
-            rdp->nextlist != NULL ||
-            rdp->nextschedlist != NULL ||
-            rdp->waitschedlist != NULL)
-                return 1;
-
-        /* The RCU core needs an acknowledgement from this CPU. */
-
-        if ((per_cpu(rcu_flip_flag, cpu) == rcu_flipped) ||
-            (per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed))
-                return 1;
-
-        /* This CPU has fallen behind the global grace-period number. */
-
-        if (rdp->completed != rcu_ctrlblk.completed)
-                return 1;
-
-        /* Nothing needed from this CPU. */
-
-        return 0;
-}
-
-int __cpuinit rcu_cpu_notify(struct notifier_block *self,
-                             unsigned long action, void *hcpu)
-{
-        long cpu = (long)hcpu;
-
-        switch (action) {
-        case CPU_UP_PREPARE:
-        case CPU_UP_PREPARE_FROZEN:
-                rcu_online_cpu(cpu);
-                break;
-        case CPU_UP_CANCELED:
-        case CPU_UP_CANCELED_FROZEN:
-        case CPU_DEAD:
-        case CPU_DEAD_FROZEN:
-                rcu_offline_cpu(cpu);
-                break;
-        default:
-                break;
-        }
-        return NOTIFY_OK;
-}
-
-void __init __rcu_init(void)
-{
-        int cpu;
-        int i;
-        struct rcu_data *rdp;
-
-        printk(KERN_NOTICE "Preemptible RCU implementation.\n");
-        for_each_possible_cpu(cpu) {
-                rdp = RCU_DATA_CPU(cpu);
-                spin_lock_init(&rdp->lock);
-                rdp->completed = 0;
-                rdp->waitlistcount = 0;
-                rdp->nextlist = NULL;
-                rdp->nexttail = &rdp->nextlist;
-                for (i = 0; i < GP_STAGES; i++) {
-                        rdp->waitlist[i] = NULL;
-                        rdp->waittail[i] = &rdp->waitlist[i];
-                }
-                rdp->donelist = NULL;
-                rdp->donetail = &rdp->donelist;
-                rdp->rcu_flipctr[0] = 0;
-                rdp->rcu_flipctr[1] = 0;
-                rdp->nextschedlist = NULL;
-                rdp->nextschedtail = &rdp->nextschedlist;
-                rdp->waitschedlist = NULL;
-                rdp->waitschedtail = &rdp->waitschedlist;
-                rdp->rcu_sched_sleeping = 0;
-        }
-        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
-}
-
-/*
- * Late-boot-time RCU initialization that must wait until after scheduler
- * has been initialized.
- */
-void __init rcu_init_sched(void)
-{
-        rcu_sched_grace_period_task = kthread_run(rcu_sched_grace_period,
-                                                  NULL,
-                                                  "rcu_sched_grace_period");
-        WARN_ON(IS_ERR(rcu_sched_grace_period_task));
-}
-
-#ifdef CONFIG_RCU_TRACE
-long *rcupreempt_flipctr(int cpu)
-{
-        return &RCU_DATA_CPU(cpu)->rcu_flipctr[0];
-}
-EXPORT_SYMBOL_GPL(rcupreempt_flipctr);
-
-int rcupreempt_flip_flag(int cpu)
-{
-        return per_cpu(rcu_flip_flag, cpu);
-}
-EXPORT_SYMBOL_GPL(rcupreempt_flip_flag);
-
-int rcupreempt_mb_flag(int cpu)
-{
-        return per_cpu(rcu_mb_flag, cpu);
-}
-EXPORT_SYMBOL_GPL(rcupreempt_mb_flag);
-
-char *rcupreempt_try_flip_state_name(void)
-{
-        return rcu_try_flip_state_names[rcu_ctrlblk.rcu_try_flip_state];
-}
-EXPORT_SYMBOL_GPL(rcupreempt_try_flip_state_name);
-
-struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu)
-{
-        struct rcu_data *rdp = RCU_DATA_CPU(cpu);
-
-        return &rdp->trace;
-}
-EXPORT_SYMBOL_GPL(rcupreempt_trace_cpu);
-
-#endif /* #ifdef RCU_TRACE */