rcu: Separately compile large rcu_segcblist functions

This commit creates a new kernel/rcu/rcu_segcblist.c file that
contains non-trivial segcblist functions.  Trivial functions
remain as static inline functions in kernel/rcu/rcu_segcblist.h

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>

4 files changed, 544 insertions, 498 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 42a346b0df43..1d3475fc9496 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -573,6 +573,9 @@ config RCU_STALL_COMMON
           the tiny variants to disable RCU CPU stall warnings, while
           making these warnings mandatory for the tree variants.
 
+config RCU_NEED_SEGCBLIST
+        def_bool ( TREE_RCU || PREEMPT_RCU || TINY_SRCU || TREE_SRCU )
+
 config CONTEXT_TRACKING
        bool
 
diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile
index 158e6593d58c..23803c7d5180 100644
--- a/kernel/rcu/Makefile
+++ b/kernel/rcu/Makefile
@@ -12,3 +12,4 @@ obj-$(CONFIG_TREE_RCU) += tree.o
 obj-$(CONFIG_PREEMPT_RCU) += tree.o
 obj-$(CONFIG_TREE_RCU_TRACE) += tree_trace.o
 obj-$(CONFIG_TINY_RCU) += tiny.o
+obj-$(CONFIG_RCU_NEED_SEGCBLIST) += rcu_segcblist.o
diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
new file mode 100644
index 000000000000..2b62a38b080f
--- /dev/null
+++ b/kernel/rcu/rcu_segcblist.c
@@ -0,0 +1,505 @@
+/*
+ * RCU segmented callback lists, function definitions
+ *
+ * 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, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright IBM Corporation, 2017
+ *
+ * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/interrupt.h>
+
+#include "rcu_segcblist.h"
+
+/* Initialize simple callback list. */
+void rcu_cblist_init(struct rcu_cblist *rclp)
+{
+        rclp->head = NULL;
+        rclp->tail = &rclp->head;
+        rclp->len = 0;
+        rclp->len_lazy = 0;
+}
+
+/*
+ * Debug function to actually count the number of callbacks.
+ * If the number exceeds the limit specified, return -1.
+ */
+long rcu_cblist_count_cbs(struct rcu_cblist *rclp, long lim)
+{
+        int cnt = 0;
+        struct rcu_head **rhpp = &rclp->head;
+
+        for (;;) {
+                if (!*rhpp)
+                        return cnt;
+                if (++cnt > lim)
+                        return -1;
+                rhpp = &(*rhpp)->next;
+        }
+}
+
+/*
+ * Dequeue the oldest rcu_head structure from the specified callback
+ * list.  This function assumes that the callback is non-lazy, but
+ * the caller can later invoke rcu_cblist_dequeued_lazy() if it
+ * finds otherwise (and if it cares about laziness).  This allows
+ * different users to have different ways of determining laziness.
+ */
+struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp)
+{
+        struct rcu_head *rhp;
+
+        rhp = rclp->head;
+        if (!rhp)
+                return NULL;
+        rclp->len--;
+        rclp->head = rhp->next;
+        if (!rclp->head)
+                rclp->tail = &rclp->head;
+        return rhp;
+}
+
+/*
+ * Initialize an rcu_segcblist structure.
+ */
+void rcu_segcblist_init(struct rcu_segcblist *rsclp)
+{
+        int i;
+
+        BUILD_BUG_ON(RCU_NEXT_TAIL + 1 != ARRAY_SIZE(rsclp->gp_seq));
+        BUILD_BUG_ON(ARRAY_SIZE(rsclp->tails) != ARRAY_SIZE(rsclp->gp_seq));
+        rsclp->head = NULL;
+        for (i = 0; i < RCU_CBLIST_NSEGS; i++)
+                rsclp->tails[i] = &rsclp->head;
+        rsclp->len = 0;
+        rsclp->len_lazy = 0;
+}
+
+/*
+ * Disable the specified rcu_segcblist structure, so that callbacks can
+ * no longer be posted to it.  This structure must be empty.
+ */
+void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
+{
+        WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
+        WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
+        WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
+        rsclp->tails[RCU_NEXT_TAIL] = NULL;
+}
+
+/*
+ * Is the specified segment of the specified rcu_segcblist structure
+ * empty of callbacks?
+ */
+bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg)
+{
+        if (seg == RCU_DONE_TAIL)
+                return &rsclp->head == rsclp->tails[RCU_DONE_TAIL];
+        return rsclp->tails[seg - 1] == rsclp->tails[seg];
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * are ready to be invoked?
+ */
+bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp)
+{
+        return rcu_segcblist_is_enabled(rsclp) &&
+               &rsclp->head != rsclp->tails[RCU_DONE_TAIL];
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * are still pending, that is, not yet ready to be invoked?
+ */
+bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp)
+{
+        return rcu_segcblist_is_enabled(rsclp) &&
+               !rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL);
+}
+
+/*
+ * Dequeue and return the first ready-to-invoke callback.  If there
+ * are no ready-to-invoke callbacks, return NULL.  Disables interrupts
+ * to avoid interference.  Does not protect from interference from other
+ * CPUs or tasks.
+ */
+struct rcu_head *rcu_segcblist_dequeue(struct rcu_segcblist *rsclp)
+{
+        unsigned long flags;
+        int i;
+        struct rcu_head *rhp;
+
+        local_irq_save(flags);
+        if (!rcu_segcblist_ready_cbs(rsclp)) {
+                local_irq_restore(flags);
+                return NULL;
+        }
+        rhp = rsclp->head;
+        BUG_ON(!rhp);
+        rsclp->head = rhp->next;
+        for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++) {
+                if (rsclp->tails[i] != &rhp->next)
+                        break;
+                rsclp->tails[i] = &rsclp->head;
+        }
+        smp_mb(); /* Dequeue before decrement for rcu_barrier(). */
+        WRITE_ONCE(rsclp->len, rsclp->len - 1);
+        local_irq_restore(flags);
+        return rhp;
+}
+
+/*
+ * Account for the fact that a previously dequeued callback turned out
+ * to be marked as lazy.
+ */
+void rcu_segcblist_dequeued_lazy(struct rcu_segcblist *rsclp)
+{
+        unsigned long flags;
+
+        local_irq_save(flags);
+        rsclp->len_lazy--;
+        local_irq_restore(flags);
+}
+
+/*
+ * Return a pointer to the first callback in the specified rcu_segcblist
+ * structure.  This is useful for diagnostics.
+ */
+struct rcu_head *rcu_segcblist_first_cb(struct rcu_segcblist *rsclp)
+{
+        if (rcu_segcblist_is_enabled(rsclp))
+                return rsclp->head;
+        return NULL;
+}
+
+/*
+ * Return a pointer to the first pending callback in the specified
+ * rcu_segcblist structure.  This is useful just after posting a given
+ * callback -- if that callback is the first pending callback, then
+ * you cannot rely on someone else having already started up the required
+ * grace period.
+ */
+struct rcu_head *rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp)
+{
+        if (rcu_segcblist_is_enabled(rsclp))
+                return *rsclp->tails[RCU_DONE_TAIL];
+        return NULL;
+}
+
+/*
+ * Does the specified rcu_segcblist structure contain callbacks that
+ * have not yet been processed beyond having been posted, that is,
+ * does it contain callbacks in its last segment?
+ */
+bool rcu_segcblist_new_cbs(struct rcu_segcblist *rsclp)
+{
+        return rcu_segcblist_is_enabled(rsclp) &&
+               !rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL);
+}
+
+/*
+ * Enqueue the specified callback onto the specified rcu_segcblist
+ * structure, updating accounting as needed.  Note that the ->len
+ * field may be accessed locklessly, hence the WRITE_ONCE().
+ * The ->len field is used by rcu_barrier() and friends to determine
+ * if it must post a callback on this structure, and it is OK
+ * for rcu_barrier() to sometimes post callbacks needlessly, but
+ * absolutely not OK for it to ever miss posting a callback.
+ */
+void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
+                           struct rcu_head *rhp, bool lazy)
+{
+        WRITE_ONCE(rsclp->len, rsclp->len + 1); /* ->len sampled locklessly. */
+        if (lazy)
+                rsclp->len_lazy++;
+        smp_mb(); /* Ensure counts are updated before callback is enqueued. */
+        rhp->next = NULL;
+        *rsclp->tails[RCU_NEXT_TAIL] = rhp;
+        rsclp->tails[RCU_NEXT_TAIL] = &rhp->next;
+}
+
+/*
+ * Entrain the specified callback onto the specified rcu_segcblist at
+ * the end of the last non-empty segment.  If the entire rcu_segcblist
+ * is empty, make no change, but return false.
+ *
+ * This is intended for use by rcu_barrier()-like primitives, -not-
+ * for normal grace-period use.  IMPORTANT:  The callback you enqueue
+ * will wait for all prior callbacks, NOT necessarily for a grace
+ * period.  You have been warned.
+ */
+bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
+                           struct rcu_head *rhp, bool lazy)
+{
+        int i;
+
+        if (rcu_segcblist_n_cbs(rsclp) == 0)
+                return false;
+        WRITE_ONCE(rsclp->len, rsclp->len + 1);
+        if (lazy)
+                rsclp->len_lazy++;
+        smp_mb(); /* Ensure counts are updated before callback is entrained. */
+        rhp->next = NULL;
+        for (i = RCU_NEXT_TAIL; i > RCU_DONE_TAIL; i--)
+                if (rsclp->tails[i] != rsclp->tails[i - 1])
+                        break;
+        *rsclp->tails[i] = rhp;
+        for (; i <= RCU_NEXT_TAIL; i++)
+                rsclp->tails[i] = &rhp->next;
+        return true;
+}
+
+/*
+ * Extract only the counts from the specified rcu_segcblist structure,
+ * and place them in the specified rcu_cblist structure.  This function
+ * supports both callback orphaning and invocation, hence the separation
+ * of counts and callbacks.  (Callbacks ready for invocation must be
+ * orphaned and adopted separately from pending callbacks, but counts
+ * apply to all callbacks.  Locking must be used to make sure that
+ * both orphaned-callbacks lists are consistent.)
+ */
+void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
+                                               struct rcu_cblist *rclp)
+{
+        rclp->len_lazy += rsclp->len_lazy;
+        rclp->len += rsclp->len;
+        rsclp->len_lazy = 0;
+        WRITE_ONCE(rsclp->len, 0); /* ->len sampled locklessly. */
+}
+
+/*
+ * Extract only those callbacks ready to be invoked from the specified
+ * rcu_segcblist structure and place them in the specified rcu_cblist
+ * structure.
+ */
+void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
+                                    struct rcu_cblist *rclp)
+{
+        int i;
+
+        if (!rcu_segcblist_ready_cbs(rsclp))
+                return; /* Nothing to do. */
+        *rclp->tail = rsclp->head;
+        rsclp->head = *rsclp->tails[RCU_DONE_TAIL];
+        *rsclp->tails[RCU_DONE_TAIL] = NULL;
+        rclp->tail = rsclp->tails[RCU_DONE_TAIL];
+        for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
+                if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
+                        rsclp->tails[i] = &rsclp->head;
+}
+
+/*
+ * Extract only those callbacks still pending (not yet ready to be
+ * invoked) from the specified rcu_segcblist structure and place them in
+ * the specified rcu_cblist structure.  Note that this loses information
+ * about any callbacks that might have been partway done waiting for
+ * their grace period.  Too bad!  They will have to start over.
+ */
+void rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
+                                    struct rcu_cblist *rclp)
+{
+        int i;
+
+        if (!rcu_segcblist_pend_cbs(rsclp))
+                return; /* Nothing to do. */
+        *rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
+        rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
+        *rsclp->tails[RCU_DONE_TAIL] = NULL;
+        for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
+                rsclp->tails[i] = rsclp->tails[RCU_DONE_TAIL];
+}
+
+/*
+ * Insert counts from the specified rcu_cblist structure in the
+ * specified rcu_segcblist structure.
+ */
+void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
+                                struct rcu_cblist *rclp)
+{
+        rsclp->len_lazy += rclp->len_lazy;
+        /* ->len sampled locklessly. */
+        WRITE_ONCE(rsclp->len, rsclp->len + rclp->len);
+        rclp->len_lazy = 0;
+        rclp->len = 0;
+}
+
+/*
+ * Move callbacks from the specified rcu_cblist to the beginning of the
+ * done-callbacks segment of the specified rcu_segcblist.
+ */
+void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
+                                   struct rcu_cblist *rclp)
+{
+        int i;
+
+        if (!rclp->head)
+                return; /* No callbacks to move. */
+        *rclp->tail = rsclp->head;
+        rsclp->head = rclp->head;
+        for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
+                if (&rsclp->head == rsclp->tails[i])
+                        rsclp->tails[i] = rclp->tail;
+                else
+                        break;
+        rclp->head = NULL;
+        rclp->tail = &rclp->head;
+}
+
+/*
+ * Move callbacks from the specified rcu_cblist to the end of the
+ * new-callbacks segment of the specified rcu_segcblist.
+ */
+void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
+                                   struct rcu_cblist *rclp)
+{
+        if (!rclp->head)
+                return; /* Nothing to do. */
+        *rsclp->tails[RCU_NEXT_TAIL] = rclp->head;
+        rsclp->tails[RCU_NEXT_TAIL] = rclp->tail;
+        rclp->head = NULL;
+        rclp->tail = &rclp->head;
+}
+
+/*
+ * Advance the callbacks in the specified rcu_segcblist structure based
+ * on the current value passed in for the grace-period counter.
+ */
+void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq)
+{
+        int i, j;
+
+        WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
+        if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL))
+                return;
+
+        /*
+         * Find all callbacks whose ->gp_seq numbers indicate that they
+         * are ready to invoke, and put them into the RCU_DONE_TAIL segment.
+         */
+        for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
+                if (ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
+                        break;
+                rsclp->tails[RCU_DONE_TAIL] = rsclp->tails[i];
+        }
+
+        /* If no callbacks moved, nothing more need be done. */
+        if (i == RCU_WAIT_TAIL)
+                return;
+
+        /* Clean up tail pointers that might have been misordered above. */
+        for (j = RCU_WAIT_TAIL; j < i; j++)
+                rsclp->tails[j] = rsclp->tails[RCU_DONE_TAIL];
+
+        /*
+         * Callbacks moved, so clean up the misordered ->tails[] pointers
+         * that now point into the middle of the list of ready-to-invoke
+         * callbacks.  The overall effect is to copy down the later pointers
+         * into the gap that was created by the now-ready segments.
+         */
+        for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
+                if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])
+                        break;  /* No more callbacks. */
+                rsclp->tails[j] = rsclp->tails[i];
+                rsclp->gp_seq[j] = rsclp->gp_seq[i];
+        }
+}
+
+/*
+ * "Accelerate" callbacks based on more-accurate grace-period information.
+ * The reason for this is that RCU does not synchronize the beginnings and
+ * ends of grace periods, and that callbacks are posted locally.  This in
+ * turn means that the callbacks must be labelled conservatively early
+ * on, as getting exact information would degrade both performance and
+ * scalability.  When more accurate grace-period information becomes
+ * available, previously posted callbacks can be "accelerated", marking
+ * them to complete at the end of the earlier grace period.
+ *
+ * This function operates on an rcu_segcblist structure, and also the
+ * grace-period sequence number seq at which new callbacks would become
+ * ready to invoke.  Returns true if there are callbacks that won't be
+ * ready to invoke until seq, false otherwise.
+ */
+bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq)
+{
+        int i;
+
+        WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
+        if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL))
+                return false;
+
+        /*
+         * Find the segment preceding the oldest segment of callbacks
+         * whose ->gp_seq[] completion is at or after that passed in via
+         * "seq", skipping any empty segments.  This oldest segment, along
+         * with any later segments, can be merged in with any newly arrived
+         * callbacks in the RCU_NEXT_TAIL segment, and assigned "seq"
+         * as their ->gp_seq[] grace-period completion sequence number.
+         */
+        for (i = RCU_NEXT_READY_TAIL; i > RCU_DONE_TAIL; i--)
+                if (rsclp->tails[i] != rsclp->tails[i - 1] &&
+                    ULONG_CMP_LT(rsclp->gp_seq[i], seq))
+                        break;
+
+        /*
+         * If all the segments contain callbacks that correspond to
+         * earlier grace-period sequence numbers than "seq", leave.
+         * Assuming that the rcu_segcblist structure has enough
+         * segments in its arrays, this can only happen if some of
+         * the non-done segments contain callbacks that really are
+         * ready to invoke.  This situation will get straightened
+         * out by the next call to rcu_segcblist_advance().
+         *
+         * Also advance to the oldest segment of callbacks whose
+         * ->gp_seq[] completion is at or after that passed in via "seq",
+         * skipping any empty segments.
+         */
+        if (++i >= RCU_NEXT_TAIL)
+                return false;
+
+        /*
+         * Merge all later callbacks, including newly arrived callbacks,
+         * into the segment located by the for-loop above.  Assign "seq"
+         * as the ->gp_seq[] value in order to correctly handle the case
+         * where there were no pending callbacks in the rcu_segcblist
+         * structure other than in the RCU_NEXT_TAIL segment.
+         */
+        for (; i < RCU_NEXT_TAIL; i++) {
+                rsclp->tails[i] = rsclp->tails[RCU_NEXT_TAIL];
+                rsclp->gp_seq[i] = seq;
+        }
+        return true;
+}
+
+/*
+ * Scan the specified rcu_segcblist structure for callbacks that need
+ * a grace period later than the one specified by "seq".  We don't look
+ * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't
+ * have a grace-period sequence number.
+ */
+bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
+                                    unsigned long seq)
+{
+        int i;
+
+        for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
+                if (rsclp->tails[i - 1] != rsclp->tails[i] &&
+                    ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
+                        return true;
+        return false;
+}
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index d98d2f9b8d59..86bc1101b806 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -1,5 +1,5 @@
 /*
- * RCU segmented callback lists
+ * RCU segmented callback lists, internal-to-rcu header file
  *
  * 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
@@ -22,15 +22,6 @@
 
 #include <linux/rcu_segcblist.h>
 
-/* Initialize simple callback list. */
-static inline void rcu_cblist_init(struct rcu_cblist *rclp)
-{
-        rclp->head = NULL;
-        rclp->tail = &rclp->head;
-        rclp->len = 0;
-        rclp->len_lazy = 0;
-}
-
 /* Is simple callback list empty? */
 static inline bool rcu_cblist_empty(struct rcu_cblist *rclp)
 {
@@ -50,45 +41,6 @@ static inline long rcu_cblist_n_lazy_cbs(struct rcu_cblist *rclp)
 }
 
 /*
- * Debug function to actually count the number of callbacks.
- * If the number exceeds the limit specified, return -1.
- */
-static inline long rcu_cblist_count_cbs(struct rcu_cblist *rclp, long lim)
-{
-        int cnt = 0;
-        struct rcu_head **rhpp = &rclp->head;
-
-        for (;;) {
-                if (!*rhpp)
-                        return cnt;
-                if (++cnt > lim)
-                        return -1;
-                rhpp = &(*rhpp)->next;
-        }
-}
-
-/*
- * Dequeue the oldest rcu_head structure from the specified callback
- * list.  This function assumes that the callback is non-lazy, but
- * the caller can later invoke rcu_cblist_dequeued_lazy() if it
- * finds otherwise (and if it cares about laziness).  This allows
- * different users to have different ways of determining laziness.
- */
-static inline struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp)
-{
-        struct rcu_head *rhp;
-
-        rhp = rclp->head;
-        if (!rhp)
-                return NULL;
-        rclp->len--;
-        rclp->head = rhp->next;
-        if (!rclp->head)
-                rclp->tail = &rclp->head;
-        return rhp;
-}
-
-/*
  * Account for the fact that a previously dequeued callback turned out
  * to be marked as lazy.
  */
@@ -118,21 +70,9 @@ static inline struct rcu_head **rcu_cblist_tail(struct rcu_cblist *rclp)
         return rclp->tail;
 }
 
-/*
- * Initialize an rcu_segcblist structure.
- */
-static inline void rcu_segcblist_init(struct rcu_segcblist *rsclp)
-{
-        int i;
-
-        BUILD_BUG_ON(RCU_NEXT_TAIL + 1 != ARRAY_SIZE(rsclp->gp_seq));
-        BUILD_BUG_ON(ARRAY_SIZE(rsclp->tails) != ARRAY_SIZE(rsclp->gp_seq));
-        rsclp->head = NULL;
-        for (i = 0; i < RCU_CBLIST_NSEGS; i++)
-                rsclp->tails[i] = &rsclp->head;
-        rsclp->len = 0;
-        rsclp->len_lazy = 0;
-}
+void rcu_cblist_init(struct rcu_cblist *rclp);
+long rcu_cblist_count_cbs(struct rcu_cblist *rclp, long lim);
+struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp);
 
 /*
  * Is the specified rcu_segcblist structure empty?
@@ -180,29 +120,6 @@ static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
 }
 
 /*
- * Disable the specified rcu_segcblist structure, so that callbacks can
- * no longer be posted to it.  This structure must be empty.
- */
-static inline void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
-{
-        WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
-        WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
-        WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
-        rsclp->tails[RCU_NEXT_TAIL] = NULL;
-}
-
-/*
- * Is the specified segment of the specified rcu_segcblist structure
- * empty of callbacks?
- */
-static inline bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg)
-{
-        if (seg == RCU_DONE_TAIL)
-                return &rsclp->head == rsclp->tails[RCU_DONE_TAIL];
-        return rsclp->tails[seg - 1] == rsclp->tails[seg];
-}
-
-/*
  * Are all segments following the specified segment of the specified
  * rcu_segcblist structure empty of callbacks?  (The specified
  * segment might well contain callbacks.)
@@ -213,417 +130,6 @@ static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
 }
 
 /*
- * Does the specified rcu_segcblist structure contain callbacks that
- * are ready to be invoked?
- */
-static inline bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp)
-{
-        return rcu_segcblist_is_enabled(rsclp) &&
-               &rsclp->head != rsclp->tails[RCU_DONE_TAIL];
-}
-
-/*
- * Does the specified rcu_segcblist structure contain callbacks that
- * are still pending, that is, not yet ready to be invoked?
- */
-static inline bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp)
-{
-        return rcu_segcblist_is_enabled(rsclp) &&
-               !rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL);
-}
-
-/*
- * Dequeue and return the first ready-to-invoke callback.  If there
- * are no ready-to-invoke callbacks, return NULL.  Disables interrupts
- * to avoid interference.  Does not protect from interference from other
- * CPUs or tasks.
- */
-static inline struct rcu_head *
-rcu_segcblist_dequeue(struct rcu_segcblist *rsclp)
-{
-        unsigned long flags;
-        int i;
-        struct rcu_head *rhp;
-
-        local_irq_save(flags);
-        if (!rcu_segcblist_ready_cbs(rsclp)) {
-                local_irq_restore(flags);
-                return NULL;
-        }
-        rhp = rsclp->head;
-        BUG_ON(!rhp);
-        rsclp->head = rhp->next;
-        for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++) {
-                if (rsclp->tails[i] != &rhp->next)
-                        break;
-                rsclp->tails[i] = &rsclp->head;
-        }
-        smp_mb(); /* Dequeue before decrement for rcu_barrier(). */
-        WRITE_ONCE(rsclp->len, rsclp->len - 1);
-        local_irq_restore(flags);
-        return rhp;
-}
-
-/*
- * Account for the fact that a previously dequeued callback turned out
- * to be marked as lazy.
- */
-static inline void rcu_segcblist_dequeued_lazy(struct rcu_segcblist *rsclp)
-{
-        unsigned long flags;
-
-        local_irq_save(flags);
-        rsclp->len_lazy--;
-        local_irq_restore(flags);
-}
-
-/*
- * Return a pointer to the first callback in the specified rcu_segcblist
- * structure.  This is useful for diagnostics.
- */
-static inline struct rcu_head *
-rcu_segcblist_first_cb(struct rcu_segcblist *rsclp)
-{
-        if (rcu_segcblist_is_enabled(rsclp))
-                return rsclp->head;
-        return NULL;
-}
-
-/*
- * Return a pointer to the first pending callback in the specified
- * rcu_segcblist structure.  This is useful just after posting a given
- * callback -- if that callback is the first pending callback, then
- * you cannot rely on someone else having already started up the required
- * grace period.
- */
-static inline struct rcu_head *
-rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp)
-{
-        if (rcu_segcblist_is_enabled(rsclp))
-                return *rsclp->tails[RCU_DONE_TAIL];
-        return NULL;
-}
-
-/*
- * Does the specified rcu_segcblist structure contain callbacks that
- * have not yet been processed beyond having been posted, that is,
- * does it contain callbacks in its last segment?
- */
-static inline bool rcu_segcblist_new_cbs(struct rcu_segcblist *rsclp)
-{
-        return rcu_segcblist_is_enabled(rsclp) &&
-               !rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL);
-}
-
-/*
- * Enqueue the specified callback onto the specified rcu_segcblist
- * structure, updating accounting as needed.  Note that the ->len
- * field may be accessed locklessly, hence the WRITE_ONCE().
- * The ->len field is used by rcu_barrier() and friends to determine
- * if it must post a callback on this structure, and it is OK
- * for rcu_barrier() to sometimes post callbacks needlessly, but
- * absolutely not OK for it to ever miss posting a callback.
- */
-static inline void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
-                                         struct rcu_head *rhp, bool lazy)
-{
-        WRITE_ONCE(rsclp->len, rsclp->len + 1); /* ->len sampled locklessly. */
-        if (lazy)
-                rsclp->len_lazy++;
-        smp_mb(); /* Ensure counts are updated before callback is enqueued. */
-        rhp->next = NULL;
-        *rsclp->tails[RCU_NEXT_TAIL] = rhp;
-        rsclp->tails[RCU_NEXT_TAIL] = &rhp->next;
-}
-
-/*
- * Entrain the specified callback onto the specified rcu_segcblist at
- * the end of the last non-empty segment.  If the entire rcu_segcblist
- * is empty, make no change, but return false.
- *
- * This is intended for use by rcu_barrier()-like primitives, -not-
- * for normal grace-period use.  IMPORTANT:  The callback you enqueue
- * will wait for all prior callbacks, NOT necessarily for a grace
- * period.  You have been warned.
- */
-static inline bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
-                                         struct rcu_head *rhp, bool lazy)
-{
-        int i;
-
-        if (rcu_segcblist_n_cbs(rsclp) == 0)
-                return false;
-        WRITE_ONCE(rsclp->len, rsclp->len + 1);
-        if (lazy)
-                rsclp->len_lazy++;
-        smp_mb(); /* Ensure counts are updated before callback is entrained. */
-        rhp->next = NULL;
-        for (i = RCU_NEXT_TAIL; i > RCU_DONE_TAIL; i--)
-                if (rsclp->tails[i] != rsclp->tails[i - 1])
-                        break;
-        *rsclp->tails[i] = rhp;
-        for (; i <= RCU_NEXT_TAIL; i++)
-                rsclp->tails[i] = &rhp->next;
-        return true;
-}
-
-/*
- * Extract only the counts from the specified rcu_segcblist structure,
- * and place them in the specified rcu_cblist structure.  This function
- * supports both callback orphaning and invocation, hence the separation
- * of counts and callbacks.  (Callbacks ready for invocation must be
- * orphaned and adopted separately from pending callbacks, but counts
- * apply to all callbacks.  Locking must be used to make sure that
- * both orphaned-callbacks lists are consistent.)
- */
-static inline void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
-                                               struct rcu_cblist *rclp)
-{
-        rclp->len_lazy += rsclp->len_lazy;
-        rclp->len += rsclp->len;
-        rsclp->len_lazy = 0;
-        WRITE_ONCE(rsclp->len, 0); /* ->len sampled locklessly. */
-}
-
-/*
- * Extract only those callbacks ready to be invoked from the specified
- * rcu_segcblist structure and place them in the specified rcu_cblist
- * structure.
- */
-static inline void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
-                                                  struct rcu_cblist *rclp)
-{
-        int i;
-
-        if (!rcu_segcblist_ready_cbs(rsclp))
-                return; /* Nothing to do. */
-        *rclp->tail = rsclp->head;
-        rsclp->head = *rsclp->tails[RCU_DONE_TAIL];
-        *rsclp->tails[RCU_DONE_TAIL] = NULL;
-        rclp->tail = rsclp->tails[RCU_DONE_TAIL];
-        for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
-                if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
-                        rsclp->tails[i] = &rsclp->head;
-}
-
-/*
- * Extract only those callbacks still pending (not yet ready to be
- * invoked) from the specified rcu_segcblist structure and place them in
- * the specified rcu_cblist structure.  Note that this loses information
- * about any callbacks that might have been partway done waiting for
- * their grace period.  Too bad!  They will have to start over.
- */
-static inline void
-rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
-                               struct rcu_cblist *rclp)
-{
-        int i;
-
-        if (!rcu_segcblist_pend_cbs(rsclp))
-                return; /* Nothing to do. */
-        *rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
-        rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
-        *rsclp->tails[RCU_DONE_TAIL] = NULL;
-        for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
-                rsclp->tails[i] = rsclp->tails[RCU_DONE_TAIL];
-}
-
-/*
- * Move the entire contents of the specified rcu_segcblist structure,
- * counts, callbacks, and all, to the specified rcu_cblist structure.
- * @@@ Why do we need this???  Moving early-boot CBs to NOCB lists?
- * @@@ Memory barrier needed?  (Not if only used at boot time...)
- */
-static inline void rcu_segcblist_extract_all(struct rcu_segcblist *rsclp,
-                                             struct rcu_cblist *rclp)
-{
-        rcu_segcblist_extract_done_cbs(rsclp, rclp);
-        rcu_segcblist_extract_pend_cbs(rsclp, rclp);
-        rcu_segcblist_extract_count(rsclp, rclp);
-}
-
-/*
- * Insert counts from the specified rcu_cblist structure in the
- * specified rcu_segcblist structure.
- */
-static inline void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
-                                              struct rcu_cblist *rclp)
-{
-        rsclp->len_lazy += rclp->len_lazy;
-        /* ->len sampled locklessly. */
-        WRITE_ONCE(rsclp->len, rsclp->len + rclp->len);
-        rclp->len_lazy = 0;
-        rclp->len = 0;
-}
-
-/*
- * Move callbacks from the specified rcu_cblist to the beginning of the
- * done-callbacks segment of the specified rcu_segcblist.
- */
-static inline void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
-                                                 struct rcu_cblist *rclp)
-{
-        int i;
-
-        if (!rclp->head)
-                return; /* No callbacks to move. */
-        *rclp->tail = rsclp->head;
-        rsclp->head = rclp->head;
-        for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
-                if (&rsclp->head == rsclp->tails[i])
-                        rsclp->tails[i] = rclp->tail;
-                else
-                        break;
-        rclp->head = NULL;
-        rclp->tail = &rclp->head;
-}
-
-/*
- * Move callbacks from the specified rcu_cblist to the end of the
- * new-callbacks segment of the specified rcu_segcblist.
- */
-static inline void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
-                                                 struct rcu_cblist *rclp)
-{
-        if (!rclp->head)
-                return; /* Nothing to do. */
-        *rsclp->tails[RCU_NEXT_TAIL] = rclp->head;
-        rsclp->tails[RCU_NEXT_TAIL] = rclp->tail;
-        rclp->head = NULL;
-        rclp->tail = &rclp->head;
-}
-
-/*
- * Advance the callbacks in the specified rcu_segcblist structure based
- * on the current value passed in for the grace-period counter.
- */
-static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp,
-                                         unsigned long seq)
-{
-        int i, j;
-
-        WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
-        if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL))
-                return;
-
-        /*
-         * Find all callbacks whose ->gp_seq numbers indicate that they
-         * are ready to invoke, and put them into the RCU_DONE_TAIL segment.
-         */
-        for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
-                if (ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
-                        break;
-                rsclp->tails[RCU_DONE_TAIL] = rsclp->tails[i];
-        }
-
-        /* If no callbacks moved, nothing more need be done. */
-        if (i == RCU_WAIT_TAIL)
-                return;
-
-        /* Clean up tail pointers that might have been misordered above. */
-        for (j = RCU_WAIT_TAIL; j < i; j++)
-                rsclp->tails[j] = rsclp->tails[RCU_DONE_TAIL];
-
-        /*
-         * Callbacks moved, so clean up the misordered ->tails[] pointers
-         * that now point into the middle of the list of ready-to-invoke
-         * callbacks.  The overall effect is to copy down the later pointers
-         * into the gap that was created by the now-ready segments.
-         */
-        for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
-                if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])
-                        break;  /* No more callbacks. */
-                rsclp->tails[j] = rsclp->tails[i];
-                rsclp->gp_seq[j] = rsclp->gp_seq[i];
-        }
-}
-
-/*
- * "Accelerate" callbacks based on more-accurate grace-period information.
- * The reason for this is that RCU does not synchronize the beginnings and
- * ends of grace periods, and that callbacks are posted locally.  This in
- * turn means that the callbacks must be labelled conservatively early
- * on, as getting exact information would degrade both performance and
- * scalability.  When more accurate grace-period information becomes
- * available, previously posted callbacks can be "accelerated", marking
- * them to complete at the end of the earlier grace period.
- *
- * This function operates on an rcu_segcblist structure, and also the
- * grace-period sequence number seq at which new callbacks would become
- * ready to invoke.  Returns true if there are callbacks that won't be
- * ready to invoke until seq, false otherwise.
- */
-static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
-                                            unsigned long seq)
-{
-        int i;
-
-        WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
-        if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL))
-                return false;
-
-        /*
-         * Find the segment preceding the oldest segment of callbacks
-         * whose ->gp_seq[] completion is at or after that passed in via
-         * "seq", skipping any empty segments.  This oldest segment, along
-         * with any later segments, can be merged in with any newly arrived
-         * callbacks in the RCU_NEXT_TAIL segment, and assigned "seq"
-         * as their ->gp_seq[] grace-period completion sequence number.
-         */
-        for (i = RCU_NEXT_READY_TAIL; i > RCU_DONE_TAIL; i--)
-                if (rsclp->tails[i] != rsclp->tails[i - 1] &&
-                    ULONG_CMP_LT(rsclp->gp_seq[i], seq))
-                        break;
-
-        /*
-         * If all the segments contain callbacks that correspond to
-         * earlier grace-period sequence numbers than "seq", leave.
-         * Assuming that the rcu_segcblist structure has enough
-         * segments in its arrays, this can only happen if some of
-         * the non-done segments contain callbacks that really are
-         * ready to invoke.  This situation will get straightened
-         * out by the next call to rcu_segcblist_advance().
-         *
-         * Also advance to the oldest segment of callbacks whose
-         * ->gp_seq[] completion is at or after that passed in via "seq",
-         * skipping any empty segments.
-         */
-        if (++i >= RCU_NEXT_TAIL)
-                return false;
-
-        /*
-         * Merge all later callbacks, including newly arrived callbacks,
-         * into the segment located by the for-loop above.  Assign "seq"
-         * as the ->gp_seq[] value in order to correctly handle the case
-         * where there were no pending callbacks in the rcu_segcblist
-         * structure other than in the RCU_NEXT_TAIL segment.
-         */
-        for (; i < RCU_NEXT_TAIL; i++) {
-                rsclp->tails[i] = rsclp->tails[RCU_NEXT_TAIL];
-                rsclp->gp_seq[i] = seq;
-        }
-        return true;
-}
-
-/*
- * Scan the specified rcu_segcblist structure for callbacks that need
- * a grace period later than the one specified by "seq".  We don't look
- * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't
- * have a grace-period sequence number.
- */
-static inline bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
-                                                  unsigned long seq)
-{
-        int i;
-
-        for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
-                if (rsclp->tails[i - 1] != rsclp->tails[i] &&
-                    ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
-                        return true;
-        return false;
-}
-
-/*
  * Interim function to return rcu_segcblist head pointer.  Longer term, the
  * rcu_segcblist will be used more pervasively, removing the need for this
  * function.
@@ -643,3 +149,34 @@ static inline struct rcu_head **rcu_segcblist_tail(struct rcu_segcblist *rsclp)
         WARN_ON_ONCE(rcu_segcblist_empty(rsclp));
         return rsclp->tails[RCU_NEXT_TAIL];
 }
+
+void rcu_segcblist_init(struct rcu_segcblist *rsclp);
+void rcu_segcblist_disable(struct rcu_segcblist *rsclp);
+bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg);
+bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp);
+bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp);
+struct rcu_head *rcu_segcblist_dequeue(struct rcu_segcblist *rsclp);
+void rcu_segcblist_dequeued_lazy(struct rcu_segcblist *rsclp);
+struct rcu_head *rcu_segcblist_first_cb(struct rcu_segcblist *rsclp);
+struct rcu_head *rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp);
+bool rcu_segcblist_new_cbs(struct rcu_segcblist *rsclp);
+void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
+                           struct rcu_head *rhp, bool lazy);
+bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
+                           struct rcu_head *rhp, bool lazy);
+void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
+                                 struct rcu_cblist *rclp);
+void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
+                                    struct rcu_cblist *rclp);
+void rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
+                                    struct rcu_cblist *rclp);
+void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
+                                struct rcu_cblist *rclp);
+void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
+                                   struct rcu_cblist *rclp);
+void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
+                                   struct rcu_cblist *rclp);
+void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq);
+bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq);
+bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
+                                    unsigned long seq);