[PATCH v3 tip/core/rcu 13/40] srcu: Abstract multi-tail callback list handling
From: Paul E. McKenney
Date: Wed Apr 19 2017 - 13:03:18 EST
RCU has only one multi-tail callback list, which is implemented via
the nxtlist, nxttail, nxtcompleted, qlen_lazy, and qlen fields in the
rcu_data structure, and whose operations are open-code throughout the
Tree RCU implementation. This has been more or less OK in the past,
but upcoming callback-list optimizations in SRCU could really use
a multi-tail callback list there as well.
This commit therefore abstracts the multi-tail callback list handling
into a new kernel/rcu/rcu_segcblist.h file, and uses this new API.
The simple head-and-tail pointer callback list is also abstracted and
applied everywhere except for the NOCB callback-offload lists. (Yes,
the plan is to apply them there as well, but this commit is already
bigger than would be good.)
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcu/rcu_segcblist.h | 625 +++++++++++++++++++++++++++++++++++++++++++++
kernel/rcu/tree.c | 348 ++++++++-----------------
kernel/rcu/tree.h | 41 +--
kernel/rcu/tree_plugin.h | 54 ++--
kernel/rcu/tree_trace.c | 21 +-
5 files changed, 780 insertions(+), 309 deletions(-)
create mode 100644 kernel/rcu/rcu_segcblist.h
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
new file mode 100644
index 000000000000..24078f3c0218
--- /dev/null
+++ b/kernel/rcu/rcu_segcblist.h
@@ -0,0 +1,625 @@
+/*
+ * RCU segmented callback lists
+ *
+ * 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@xxxxxxxxxxxxxxxxxx>
+ */
+
+#ifndef __KERNEL_RCU_SEGCBLIST_H
+#define __KERNEL_RCU_SEGCBLIST_H
+
+/* Simple unsegmented callback lists. */
+struct rcu_cblist {
+ struct rcu_head *head;
+ struct rcu_head **tail;
+ long len;
+ long len_lazy;
+};
+
+#define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
+
+/* 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)
+{
+ return !rclp->head;
+}
+
+/* Return number of callbacks in simple callback list. */
+static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
+{
+ return rclp->len;
+}
+
+/* Return number of lazy callbacks in simple callback list. */
+static inline long rcu_cblist_n_lazy_cbs(struct rcu_cblist *rclp)
+{
+ return rclp->len_lazy;
+}
+
+/*
+ * 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;
+ prefetch(rhp);
+ 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.
+ */
+static inline void rcu_cblist_dequeued_lazy(struct rcu_cblist *rclp)
+{
+ rclp->len_lazy--;
+}
+
+/*
+ * Interim function to return rcu_cblist head pointer. Longer term, the
+ * rcu_cblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head *rcu_cblist_head(struct rcu_cblist *rclp)
+{
+ return rclp->head;
+}
+
+/*
+ * Interim function to return rcu_cblist head pointer. Longer term, the
+ * rcu_cblist will be used more pervasively, removing the need for this
+ * function.
+ */
+static inline struct rcu_head **rcu_cblist_tail(struct rcu_cblist *rclp)
+{
+ WARN_ON_ONCE(rcu_cblist_empty(rclp));
+ return rclp->tail;
+}
+
+/* Complicated segmented callback lists. ;-) */
+
+/*
+ * Index values for segments in rcu_segcblist structure.
+ *
+ * The segments are as follows:
+ *
+ * [head, *tails[RCU_DONE_TAIL]):
+ * Callbacks whose grace period has elapsed, and thus can be invoked.
+ * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
+ * Callbacks waiting for the current GP from the current CPU's viewpoint.
+ * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
+ * Callbacks that arrived before the next GP started, again from
+ * the current CPU's viewpoint. These can be handled by the next GP.
+ * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
+ * Callbacks that might have arrived after the next GP started.
+ * There is some uncertainty as to when a given GP starts and
+ * ends, but a CPU knows the exact times if it is the one starting
+ * or ending the GP. Other CPUs know that the previous GP ends
+ * before the next one starts.
+ *
+ * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
+ * empty.
+ *
+ * The ->gp_seq[] array contains the grace-period number at which the
+ * corresponding segment of callbacks will be ready to invoke. A given
+ * element of this array is meaningful only when the corresponding segment
+ * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
+ * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
+ * not yet been assigned a grace-period number).
+ */
+#define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */
+#define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */
+#define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */
+#define RCU_NEXT_TAIL 3
+#define RCU_CBLIST_NSEGS 4
+
+struct rcu_segcblist {
+ struct rcu_head *head;
+ struct rcu_head **tails[RCU_CBLIST_NSEGS];
+ unsigned long gp_seq[RCU_CBLIST_NSEGS];
+ long len;
+ long len_lazy;
+};
+
+/*
+ * 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;
+}
+
+/*
+ * Is the specified rcu_segcblist structure empty?
+ *
+ * But careful! The fact that the ->head field is NULL does not
+ * necessarily imply that there are no callbacks associated with
+ * this structure. When callbacks are being invoked, they are
+ * removed as a group. If callback invocation must be preempted,
+ * the remaining callbacks will be added back to the list. Either
+ * way, the counts are updated later.
+ *
+ * So it is often the case that rcu_segcblist_n_cbs() should be used
+ * instead.
+ */
+static inline bool rcu_segcblist_empty(struct rcu_segcblist *rsclp)
+{
+ return !rsclp->head;
+}
+
+/* Return number of callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
+{
+ return READ_ONCE(rsclp->len);
+}
+
+/* Return number of lazy callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_lazy_cbs(struct rcu_segcblist *rsclp)
+{
+ return rsclp->len_lazy;
+}
+
+/* Return number of lazy callbacks in segmented callback list. */
+static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
+{
+ return rsclp->len - rsclp->len_lazy;
+}
+
+/*
+ * Is the specified rcu_segcblist enabled, for example, not corresponding
+ * to an offline or callback-offloaded CPU?
+ */
+static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
+{
+ return !!rsclp->tails[RCU_NEXT_TAIL];
+}
+
+/*
+ * 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.)
+ */
+static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
+{
+ return !*rsclp->tails[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);
+}
+
+/*
+ * 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;
+}
+
+/*
+ * 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));
+ WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+
+ /*
+ * 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 at which new callbacks would become
+ * ready to invoke.
+ */
+static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp,
+ unsigned long seq)
+{
+ int i;
+
+ WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
+ WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL));
+
+ /*
+ * 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.
+ */
+static inline struct rcu_head *rcu_segcblist_head(struct rcu_segcblist *rsclp)
+{
+ return rsclp->head;
+}
+
+/*
+ * Interim function to return rcu_segcblist head pointer. Longer term, the
+ * rcu_segcblist will be used more pervasively, removing the need for this
+ * function.
+ */
+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];
+}
+
+#endif /* __KERNEL_RCU_SEGCBLIST_H */
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 530ab6cf7a0b..8cc9d40b41ea 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -97,8 +97,8 @@ struct rcu_state sname##_state = { \
.gpnum = 0UL - 300UL, \
.completed = 0UL - 300UL, \
.orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
- .orphan_nxttail = &sname##_state.orphan_nxtlist, \
- .orphan_donetail = &sname##_state.orphan_donelist, \
+ .orphan_pend = RCU_CBLIST_INITIALIZER(sname##_state.orphan_pend), \
+ .orphan_done = RCU_CBLIST_INITIALIZER(sname##_state.orphan_done), \
.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
.name = RCU_STATE_NAME(sname), \
.abbr = sabbr, \
@@ -726,16 +726,6 @@ void rcutorture_record_progress(unsigned long vernum)
EXPORT_SYMBOL_GPL(rcutorture_record_progress);
/*
- * Does the CPU have callbacks ready to be invoked?
- */
-static int
-cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
-{
- return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
- rdp->nxttail[RCU_NEXT_TAIL] != NULL;
-}
-
-/*
* Return the root node of the specified rcu_state structure.
*/
static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
@@ -765,21 +755,17 @@ static int rcu_future_needs_gp(struct rcu_state *rsp)
static bool
cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
{
- int i;
-
if (rcu_gp_in_progress(rsp))
return false; /* No, a grace period is already in progress. */
if (rcu_future_needs_gp(rsp))
return true; /* Yes, a no-CBs CPU needs one. */
- if (!rdp->nxttail[RCU_NEXT_TAIL])
+ if (!rcu_segcblist_is_enabled(&rdp->cblist))
return false; /* No, this is a no-CBs (or offline) CPU. */
- if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
+ if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
return true; /* Yes, CPU has newly registered callbacks. */
- for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
- if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
- ULONG_CMP_LT(READ_ONCE(rsp->completed),
- rdp->nxtcompleted[i]))
- return true; /* Yes, CBs for future grace period. */
+ if (rcu_segcblist_future_gp_needed(&rdp->cblist,
+ READ_ONCE(rsp->completed)))
+ return true; /* Yes, CBs for future grace period. */
return false; /* No grace period needed. */
}
@@ -1490,7 +1476,8 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
print_cpu_stall_info_end();
for_each_possible_cpu(cpu)
- totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
+ totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
+ cpu)->cblist);
pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
smp_processor_id(), (long)(jiffies - rsp->gp_start),
(long)rsp->gpnum, (long)rsp->completed, totqlen);
@@ -1544,7 +1531,8 @@ static void print_cpu_stall(struct rcu_state *rsp)
print_cpu_stall_info(rsp, smp_processor_id());
print_cpu_stall_info_end();
for_each_possible_cpu(cpu)
- totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
+ totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
+ cpu)->cblist);
pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
jiffies - rsp->gp_start,
(long)rsp->gpnum, (long)rsp->completed, totqlen);
@@ -1647,30 +1635,6 @@ void rcu_cpu_stall_reset(void)
}
/*
- * Initialize the specified rcu_data structure's default callback list
- * to empty. The default callback list is the one that is not used by
- * no-callbacks CPUs.
- */
-static void init_default_callback_list(struct rcu_data *rdp)
-{
- int i;
-
- rdp->nxtlist = NULL;
- for (i = 0; i < RCU_NEXT_SIZE; i++)
- rdp->nxttail[i] = &rdp->nxtlist;
-}
-
-/*
- * Initialize the specified rcu_data structure's callback list to empty.
- */
-static void init_callback_list(struct rcu_data *rdp)
-{
- if (init_nocb_callback_list(rdp))
- return;
- init_default_callback_list(rdp);
-}
-
-/*
* Determine the value that ->completed will have at the end of the
* next subsequent grace period. This is used to tag callbacks so that
* a CPU can invoke callbacks in a timely fashion even if that CPU has
@@ -1724,7 +1688,6 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
unsigned long *c_out)
{
unsigned long c;
- int i;
bool ret = false;
struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
@@ -1770,13 +1733,11 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
/*
* Get a new grace-period number. If there really is no grace
* period in progress, it will be smaller than the one we obtained
- * earlier. Adjust callbacks as needed. Note that even no-CBs
- * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
+ * earlier. Adjust callbacks as needed.
*/
c = rcu_cbs_completed(rdp->rsp, rnp_root);
- for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
- if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
- rdp->nxtcompleted[i] = c;
+ if (!rcu_is_nocb_cpu(rdp->cpu))
+ (void)rcu_segcblist_accelerate(&rdp->cblist, c);
/*
* If the needed for the required grace period is already
@@ -1856,57 +1817,27 @@ static void rcu_gp_kthread_wake(struct rcu_state *rsp)
static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
struct rcu_data *rdp)
{
- unsigned long c;
- int i;
- bool ret;
-
- /* If the CPU has no callbacks, nothing to do. */
- if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
- return false;
-
- /*
- * Starting from the sublist containing the callbacks most
- * recently assigned a ->completed number and working down, find the
- * first sublist that is not assignable to an upcoming grace period.
- * Such a sublist has something in it (first two tests) and has
- * a ->completed number assigned that will complete sooner than
- * the ->completed number for newly arrived callbacks (last test).
- *
- * The key point is that any later sublist can be assigned the
- * same ->completed number as the newly arrived callbacks, which
- * means that the callbacks in any of these later sublist can be
- * grouped into a single sublist, whether or not they have already
- * been assigned a ->completed number.
- */
- c = rcu_cbs_completed(rsp, rnp);
- for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
- if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
- !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
- break;
+ bool ret = false;
- /*
- * If there are no sublist for unassigned callbacks, leave.
- * At the same time, advance "i" one sublist, so that "i" will
- * index into the sublist where all the remaining callbacks should
- * be grouped into.
- */
- if (++i >= RCU_NEXT_TAIL)
+ /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
+ if (!rcu_segcblist_pend_cbs(&rdp->cblist))
return false;
/*
- * Assign all subsequent callbacks' ->completed number to the next
- * full grace period and group them all in the sublist initially
- * indexed by "i".
+ * Callbacks are often registered with incomplete grace-period
+ * information. Something about the fact that getting exact
+ * information requires acquiring a global lock... RCU therefore
+ * makes a conservative estimate of the grace period number at which
+ * a given callback will become ready to invoke. The following
+ * code checks this estimate and improves it when possible, thus
+ * accelerating callback invocation to an earlier grace-period
+ * number.
*/
- for (; i <= RCU_NEXT_TAIL; i++) {
- rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
- rdp->nxtcompleted[i] = c;
- }
- /* Record any needed additional grace periods. */
- ret = rcu_start_future_gp(rnp, rdp, NULL);
+ if (rcu_segcblist_accelerate(&rdp->cblist, rcu_cbs_completed(rsp, rnp)))
+ ret = rcu_start_future_gp(rnp, rdp, NULL);
/* Trace depending on how much we were able to accelerate. */
- if (!*rdp->nxttail[RCU_WAIT_TAIL])
+ if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
else
trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
@@ -1926,32 +1857,15 @@ static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
struct rcu_data *rdp)
{
- int i, j;
-
- /* If the CPU has no callbacks, nothing to do. */
- if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
+ /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
+ if (!rcu_segcblist_pend_cbs(&rdp->cblist))
return false;
/*
* Find all callbacks whose ->completed numbers indicate that they
* are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
*/
- for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
- if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
- break;
- rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
- }
- /* Clean up any sublist tail pointers that were misordered above. */
- for (j = RCU_WAIT_TAIL; j < i; j++)
- rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];
-
- /* Copy down callbacks to fill in empty sublists. */
- for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
- if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
- break;
- rdp->nxttail[j] = rdp->nxttail[i];
- rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
- }
+ rcu_segcblist_advance(&rdp->cblist, rnp->completed);
/* Classify any remaining callbacks. */
return rcu_accelerate_cbs(rsp, rnp, rdp);
@@ -2668,13 +2582,8 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
* because _rcu_barrier() excludes CPU-hotplug operations, so it
* cannot be running now. Thus no memory barrier is required.
*/
- if (rdp->nxtlist != NULL) {
- rsp->qlen_lazy += rdp->qlen_lazy;
- rsp->qlen += rdp->qlen;
- rdp->n_cbs_orphaned += rdp->qlen;
- rdp->qlen_lazy = 0;
- WRITE_ONCE(rdp->qlen, 0);
- }
+ rdp->n_cbs_orphaned += rcu_segcblist_n_cbs(&rdp->cblist);
+ rcu_segcblist_extract_count(&rdp->cblist, &rsp->orphan_done);
/*
* Next, move those callbacks still needing a grace period to
@@ -2682,31 +2591,18 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
* Some of the callbacks might have gone partway through a grace
* period, but that is too bad. They get to start over because we
* cannot assume that grace periods are synchronized across CPUs.
- * We don't bother updating the ->nxttail[] array yet, instead
- * we just reset the whole thing later on.
*/
- if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
- *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
- rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
- *rdp->nxttail[RCU_DONE_TAIL] = NULL;
- }
+ rcu_segcblist_extract_pend_cbs(&rdp->cblist, &rsp->orphan_pend);
/*
* Then move the ready-to-invoke callbacks to the orphanage,
* where some other CPU will pick them up. These will not be
* required to pass though another grace period: They are done.
*/
- if (rdp->nxtlist != NULL) {
- *rsp->orphan_donetail = rdp->nxtlist;
- rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
- }
+ rcu_segcblist_extract_done_cbs(&rdp->cblist, &rsp->orphan_done);
- /*
- * Finally, initialize the rcu_data structure's list to empty and
- * disallow further callbacks on this CPU.
- */
- init_callback_list(rdp);
- rdp->nxttail[RCU_NEXT_TAIL] = NULL;
+ /* Finally, disallow further callbacks on this CPU. */
+ rcu_segcblist_disable(&rdp->cblist);
}
/*
@@ -2715,7 +2611,6 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
*/
static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
{
- int i;
struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
/* No-CBs CPUs are handled specially. */
@@ -2724,13 +2619,11 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
return;
/* Do the accounting first. */
- rdp->qlen_lazy += rsp->qlen_lazy;
- rdp->qlen += rsp->qlen;
- rdp->n_cbs_adopted += rsp->qlen;
- if (rsp->qlen_lazy != rsp->qlen)
+ rdp->n_cbs_adopted += rcu_cblist_n_cbs(&rsp->orphan_done);
+ if (rcu_cblist_n_lazy_cbs(&rsp->orphan_done) !=
+ rcu_cblist_n_cbs(&rsp->orphan_done))
rcu_idle_count_callbacks_posted();
- rsp->qlen_lazy = 0;
- rsp->qlen = 0;
+ rcu_segcblist_insert_count(&rdp->cblist, &rsp->orphan_done);
/*
* We do not need a memory barrier here because the only way we
@@ -2738,24 +2631,13 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
* we are the task doing the rcu_barrier().
*/
- /* First adopt the ready-to-invoke callbacks. */
- if (rsp->orphan_donelist != NULL) {
- *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
- *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
- for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
- if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
- rdp->nxttail[i] = rsp->orphan_donetail;
- rsp->orphan_donelist = NULL;
- rsp->orphan_donetail = &rsp->orphan_donelist;
- }
-
- /* And then adopt the callbacks that still need a grace period. */
- if (rsp->orphan_nxtlist != NULL) {
- *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
- rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
- rsp->orphan_nxtlist = NULL;
- rsp->orphan_nxttail = &rsp->orphan_nxtlist;
- }
+ /* First adopt the ready-to-invoke callbacks, then the done ones. */
+ rcu_segcblist_insert_done_cbs(&rdp->cblist, &rsp->orphan_done);
+ WARN_ON_ONCE(!rcu_cblist_empty(&rsp->orphan_done));
+ rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rsp->orphan_pend);
+ WARN_ON_ONCE(!rcu_cblist_empty(&rsp->orphan_pend));
+ WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) !=
+ !rcu_segcblist_n_cbs(&rdp->cblist));
}
/*
@@ -2843,9 +2725,11 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
rcu_adopt_orphan_cbs(rsp, flags);
raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags);
- WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
- "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
- cpu, rdp->qlen, rdp->nxtlist);
+ WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
+ !rcu_segcblist_empty(&rdp->cblist),
+ "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
+ cpu, rcu_segcblist_n_cbs(&rdp->cblist),
+ rcu_segcblist_first_cb(&rdp->cblist));
}
/*
@@ -2855,14 +2739,17 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
- struct rcu_head *next, *list, **tail;
- long bl, count, count_lazy;
- int i;
+ struct rcu_head *rhp;
+ struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
+ long bl, count;
/* If no callbacks are ready, just return. */
- if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
- trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
- trace_rcu_batch_end(rsp->name, 0, !!READ_ONCE(rdp->nxtlist),
+ if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
+ trace_rcu_batch_start(rsp->name,
+ rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+ rcu_segcblist_n_cbs(&rdp->cblist), 0);
+ trace_rcu_batch_end(rsp->name, 0,
+ !rcu_segcblist_empty(&rdp->cblist),
need_resched(), is_idle_task(current),
rcu_is_callbacks_kthread());
return;
@@ -2870,73 +2757,62 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
/*
* Extract the list of ready callbacks, disabling to prevent
- * races with call_rcu() from interrupt handlers.
+ * races with call_rcu() from interrupt handlers. Leave the
+ * callback counts, as rcu_barrier() needs to be conservative.
*/
local_irq_save(flags);
WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
bl = rdp->blimit;
- trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
- list = rdp->nxtlist;
- rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
- *rdp->nxttail[RCU_DONE_TAIL] = NULL;
- tail = rdp->nxttail[RCU_DONE_TAIL];
- for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
- if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
- rdp->nxttail[i] = &rdp->nxtlist;
+ trace_rcu_batch_start(rsp->name, rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+ rcu_segcblist_n_cbs(&rdp->cblist), bl);
+ rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
local_irq_restore(flags);
/* Invoke callbacks. */
- count = count_lazy = 0;
- while (list) {
- next = list->next;
- prefetch(next);
- debug_rcu_head_unqueue(list);
- if (__rcu_reclaim(rsp->name, list))
- count_lazy++;
- list = next;
- /* Stop only if limit reached and CPU has something to do. */
- if (++count >= bl &&
+ rhp = rcu_cblist_dequeue(&rcl);
+ for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
+ debug_rcu_head_unqueue(rhp);
+ if (__rcu_reclaim(rsp->name, rhp))
+ rcu_cblist_dequeued_lazy(&rcl);
+ /*
+ * Stop only if limit reached and CPU has something to do.
+ * Note: The rcl structure counts down from zero.
+ */
+ if (-rcu_cblist_n_cbs(&rcl) >= bl &&
(need_resched() ||
(!is_idle_task(current) && !rcu_is_callbacks_kthread())))
break;
}
local_irq_save(flags);
- trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
- is_idle_task(current),
+ count = -rcu_cblist_n_cbs(&rcl);
+ trace_rcu_batch_end(rsp->name, count, !rcu_cblist_empty(&rcl),
+ need_resched(), is_idle_task(current),
rcu_is_callbacks_kthread());
- /* Update count, and requeue any remaining callbacks. */
- if (list != NULL) {
- *tail = rdp->nxtlist;
- rdp->nxtlist = list;
- for (i = 0; i < RCU_NEXT_SIZE; i++)
- if (&rdp->nxtlist == rdp->nxttail[i])
- rdp->nxttail[i] = tail;
- else
- break;
- }
+ /* Update counts and requeue any remaining callbacks. */
+ rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
smp_mb(); /* List handling before counting for rcu_barrier(). */
- rdp->qlen_lazy -= count_lazy;
- WRITE_ONCE(rdp->qlen, rdp->qlen - count);
rdp->n_cbs_invoked += count;
+ rcu_segcblist_insert_count(&rdp->cblist, &rcl);
/* Reinstate batch limit if we have worked down the excess. */
- if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
+ count = rcu_segcblist_n_cbs(&rdp->cblist);
+ if (rdp->blimit == LONG_MAX && count <= qlowmark)
rdp->blimit = blimit;
/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
- if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
+ if (count == 0 && rdp->qlen_last_fqs_check != 0) {
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rsp->n_force_qs;
- } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
- rdp->qlen_last_fqs_check = rdp->qlen;
- WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
+ } else if (count < rdp->qlen_last_fqs_check - qhimark)
+ rdp->qlen_last_fqs_check = count;
+ WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0));
local_irq_restore(flags);
/* Re-invoke RCU core processing if there are callbacks remaining. */
- if (cpu_has_callbacks_ready_to_invoke(rdp))
+ if (rcu_segcblist_ready_cbs(&rdp->cblist))
invoke_rcu_core();
}
@@ -3120,7 +2996,7 @@ __rcu_process_callbacks(struct rcu_state *rsp)
}
/* If there are callbacks ready, invoke them. */
- if (cpu_has_callbacks_ready_to_invoke(rdp))
+ if (rcu_segcblist_ready_cbs(&rdp->cblist))
invoke_rcu_callbacks(rsp, rdp);
/* Do any needed deferred wakeups of rcuo kthreads. */
@@ -3192,7 +3068,8 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
* invoking force_quiescent_state() if the newly enqueued callback
* is the only one waiting for a grace period to complete.
*/
- if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
+ if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
+ rdp->qlen_last_fqs_check + qhimark)) {
/* Are we ignoring a completed grace period? */
note_gp_changes(rsp, rdp);
@@ -3210,10 +3087,10 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
/* Give the grace period a kick. */
rdp->blimit = LONG_MAX;
if (rsp->n_force_qs == rdp->n_force_qs_snap &&
- *rdp->nxttail[RCU_DONE_TAIL] != head)
+ rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
force_quiescent_state(rsp);
rdp->n_force_qs_snap = rsp->n_force_qs;
- rdp->qlen_last_fqs_check = rdp->qlen;
+ rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
}
}
}
@@ -3253,7 +3130,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func,
rdp = this_cpu_ptr(rsp->rda);
/* Add the callback to our list. */
- if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
+ if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist)) || cpu != -1) {
int offline;
if (cpu != -1)
@@ -3272,23 +3149,21 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func,
*/
BUG_ON(cpu != -1);
WARN_ON_ONCE(!rcu_is_watching());
- if (!likely(rdp->nxtlist))
- init_default_callback_list(rdp);
+ if (rcu_segcblist_empty(&rdp->cblist))
+ rcu_segcblist_init(&rdp->cblist);
}
- WRITE_ONCE(rdp->qlen, rdp->qlen + 1);
- if (lazy)
- rdp->qlen_lazy++;
- else
+ rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
+ if (!lazy)
rcu_idle_count_callbacks_posted();
- smp_mb(); /* Count before adding callback for rcu_barrier(). */
- *rdp->nxttail[RCU_NEXT_TAIL] = head;
- rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
if (__is_kfree_rcu_offset((unsigned long)func))
trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
- rdp->qlen_lazy, rdp->qlen);
+ rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+ rcu_segcblist_n_cbs(&rdp->cblist));
else
- trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
+ trace_rcu_callback(rsp->name, head,
+ rcu_segcblist_n_lazy_cbs(&rdp->cblist),
+ rcu_segcblist_n_cbs(&rdp->cblist));
/* Go handle any RCU core processing required. */
__call_rcu_core(rsp, rdp, head, flags);
@@ -3600,7 +3475,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
}
/* Does this CPU have callbacks ready to invoke? */
- if (cpu_has_callbacks_ready_to_invoke(rdp)) {
+ if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
rdp->n_rp_cb_ready++;
return 1;
}
@@ -3664,10 +3539,10 @@ static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
for_each_rcu_flavor(rsp) {
rdp = this_cpu_ptr(rsp->rda);
- if (!rdp->nxtlist)
+ if (rcu_segcblist_empty(&rdp->cblist))
continue;
hc = true;
- if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
+ if (rcu_segcblist_n_nonlazy_cbs(&rdp->cblist) || !all_lazy) {
al = false;
break;
}
@@ -3776,7 +3651,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
__call_rcu(&rdp->barrier_head,
rcu_barrier_callback, rsp, cpu, 0);
}
- } else if (READ_ONCE(rdp->qlen)) {
+ } else if (rcu_segcblist_n_cbs(&rdp->cblist)) {
_rcu_barrier_trace(rsp, "OnlineQ", cpu,
rsp->barrier_sequence);
smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
@@ -3885,8 +3760,9 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rsp->n_force_qs;
rdp->blimit = blimit;
- if (!rdp->nxtlist)
- init_callback_list(rdp); /* Re-enable callbacks on this CPU. */
+ if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
+ !init_nocb_callback_list(rdp))
+ rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
rcu_sysidle_init_percpu_data(rdp->dynticks);
rcu_dynticks_eqs_online();
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 376c01e539c7..93889ff21dbb 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -30,6 +30,7 @@
#include <linux/seqlock.h>
#include <linux/swait.h>
#include <linux/stop_machine.h>
+#include "rcu_segcblist.h"
/*
* Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and
@@ -335,34 +336,9 @@ struct rcu_data {
/* period it is aware of. */
/* 2) batch handling */
- /*
- * If nxtlist is not NULL, it is partitioned as follows.
- * Any of the partitions might be empty, in which case the
- * pointer to that partition will be equal to the pointer for
- * the following partition. When the list is empty, all of
- * the nxttail elements point to the ->nxtlist pointer itself,
- * which in that case is NULL.
- *
- * [nxtlist, *nxttail[RCU_DONE_TAIL]):
- * Entries that batch # <= ->completed
- * The grace period for these entries has completed, and
- * the other grace-period-completed entries may be moved
- * here temporarily in rcu_process_callbacks().
- * [*nxttail[RCU_DONE_TAIL], *nxttail[RCU_WAIT_TAIL]):
- * Entries that batch # <= ->completed - 1: waiting for current GP
- * [*nxttail[RCU_WAIT_TAIL], *nxttail[RCU_NEXT_READY_TAIL]):
- * Entries known to have arrived before current GP ended
- * [*nxttail[RCU_NEXT_READY_TAIL], *nxttail[RCU_NEXT_TAIL]):
- * Entries that might have arrived after current GP ended
- * Note that the value of *nxttail[RCU_NEXT_TAIL] will
- * always be NULL, as this is the end of the list.
- */
- struct rcu_head *nxtlist;
- struct rcu_head **nxttail[RCU_NEXT_SIZE];
- unsigned long nxtcompleted[RCU_NEXT_SIZE];
- /* grace periods for sublists. */
- long qlen_lazy; /* # of lazy queued callbacks */
- long qlen; /* # of queued callbacks, incl lazy */
+ struct rcu_segcblist cblist; /* Segmented callback list, with */
+ /* different callbacks waiting for */
+ /* different grace periods. */
long qlen_last_fqs_check;
/* qlen at last check for QS forcing */
unsigned long n_cbs_invoked; /* count of RCU cbs invoked. */
@@ -500,14 +476,11 @@ struct rcu_state {
raw_spinlock_t orphan_lock ____cacheline_internodealigned_in_smp;
/* Protect following fields. */
- struct rcu_head *orphan_nxtlist; /* Orphaned callbacks that */
+ struct rcu_cblist orphan_pend; /* Orphaned callbacks that */
/* need a grace period. */
- struct rcu_head **orphan_nxttail; /* Tail of above. */
- struct rcu_head *orphan_donelist; /* Orphaned callbacks that */
+ struct rcu_cblist orphan_done; /* Orphaned callbacks that */
/* are ready to invoke. */
- struct rcu_head **orphan_donetail; /* Tail of above. */
- long qlen_lazy; /* Number of lazy callbacks. */
- long qlen; /* Total number of callbacks. */
+ /* (Contains counts.) */
/* End of fields guarded by orphan_lock. */
struct mutex barrier_mutex; /* Guards barrier fields. */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 621296a6694b..f88356652dcf 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1350,10 +1350,10 @@ static bool __maybe_unused rcu_try_advance_all_cbs(void)
*/
if ((rdp->completed != rnp->completed ||
unlikely(READ_ONCE(rdp->gpwrap))) &&
- rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
+ rcu_segcblist_pend_cbs(&rdp->cblist))
note_gp_changes(rsp, rdp);
- if (cpu_has_callbacks_ready_to_invoke(rdp))
+ if (rcu_segcblist_ready_cbs(&rdp->cblist))
cbs_ready = true;
}
return cbs_ready;
@@ -1461,7 +1461,7 @@ static void rcu_prepare_for_idle(void)
rdtp->last_accelerate = jiffies;
for_each_rcu_flavor(rsp) {
rdp = this_cpu_ptr(rsp->rda);
- if (!*rdp->nxttail[RCU_DONE_TAIL])
+ if (rcu_segcblist_pend_cbs(&rdp->cblist))
continue;
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
@@ -1529,7 +1529,7 @@ static void rcu_oom_notify_cpu(void *unused)
for_each_rcu_flavor(rsp) {
rdp = raw_cpu_ptr(rsp->rda);
- if (rdp->qlen_lazy != 0) {
+ if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) {
atomic_inc(&oom_callback_count);
rsp->call(&rdp->oom_head, rcu_oom_callback);
}
@@ -1934,30 +1934,26 @@ static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
struct rcu_data *rdp,
unsigned long flags)
{
- long ql = rsp->qlen;
- long qll = rsp->qlen_lazy;
+ long ql = rcu_cblist_n_cbs(&rsp->orphan_done);
+ long qll = rcu_cblist_n_lazy_cbs(&rsp->orphan_done);
/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
if (!rcu_is_nocb_cpu(smp_processor_id()))
return false;
- rsp->qlen = 0;
- rsp->qlen_lazy = 0;
/* First, enqueue the donelist, if any. This preserves CB ordering. */
- if (rsp->orphan_donelist != NULL) {
- __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
- rsp->orphan_donetail, ql, qll, flags);
- ql = qll = 0;
- rsp->orphan_donelist = NULL;
- rsp->orphan_donetail = &rsp->orphan_donelist;
+ if (!rcu_cblist_empty(&rsp->orphan_done)) {
+ __call_rcu_nocb_enqueue(rdp, rcu_cblist_head(&rsp->orphan_done),
+ rcu_cblist_tail(&rsp->orphan_done),
+ ql, qll, flags);
}
- if (rsp->orphan_nxtlist != NULL) {
- __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
- rsp->orphan_nxttail, ql, qll, flags);
- ql = qll = 0;
- rsp->orphan_nxtlist = NULL;
- rsp->orphan_nxttail = &rsp->orphan_nxtlist;
+ if (!rcu_cblist_empty(&rsp->orphan_pend)) {
+ __call_rcu_nocb_enqueue(rdp, rcu_cblist_head(&rsp->orphan_pend),
+ rcu_cblist_tail(&rsp->orphan_pend),
+ ql, qll, flags);
}
+ rcu_cblist_init(&rsp->orphan_done);
+ rcu_cblist_init(&rsp->orphan_pend);
return true;
}
@@ -2399,16 +2395,16 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
return false;
/* If there are early-boot callbacks, move them to nocb lists. */
- if (rdp->nxtlist) {
- rdp->nocb_head = rdp->nxtlist;
- rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL];
- atomic_long_set(&rdp->nocb_q_count, rdp->qlen);
- atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy);
- rdp->nxtlist = NULL;
- rdp->qlen = 0;
- rdp->qlen_lazy = 0;
+ if (!rcu_segcblist_empty(&rdp->cblist)) {
+ rdp->nocb_head = rcu_segcblist_head(&rdp->cblist);
+ rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist);
+ atomic_long_set(&rdp->nocb_q_count,
+ rcu_segcblist_n_cbs(&rdp->cblist));
+ atomic_long_set(&rdp->nocb_q_count_lazy,
+ rcu_segcblist_n_lazy_cbs(&rdp->cblist));
+ rcu_segcblist_init(&rdp->cblist);
}
- rdp->nxttail[RCU_NEXT_TAIL] = NULL;
+ rcu_segcblist_disable(&rdp->cblist);
return true;
}
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index 65b43be38e68..066c64071a7b 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -41,6 +41,7 @@
#include <linux/mutex.h>
#include <linux/debugfs.h>
#include <linux/seq_file.h>
+#include <linux/prefetch.h>
#define RCU_TREE_NONCORE
#include "tree.h"
@@ -128,17 +129,15 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks_fqs);
seq_printf(m, " of=%lu", rdp->offline_fqs);
rcu_nocb_q_lengths(rdp, &ql, &qll);
- qll += rdp->qlen_lazy;
- ql += rdp->qlen;
+ qll += rcu_segcblist_n_lazy_cbs(&rdp->cblist);
+ ql += rcu_segcblist_n_cbs(&rdp->cblist);
seq_printf(m, " ql=%ld/%ld qs=%c%c%c%c",
qll, ql,
- ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
- rdp->nxttail[RCU_NEXT_TAIL]],
- ".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
- rdp->nxttail[RCU_NEXT_READY_TAIL]],
- ".W"[rdp->nxttail[RCU_DONE_TAIL] !=
- rdp->nxttail[RCU_WAIT_TAIL]],
- ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
+ ".N"[!rcu_segcblist_segempty(&rdp->cblist, RCU_NEXT_TAIL)],
+ ".R"[!rcu_segcblist_segempty(&rdp->cblist,
+ RCU_NEXT_READY_TAIL)],
+ ".W"[!rcu_segcblist_segempty(&rdp->cblist, RCU_WAIT_TAIL)],
+ ".D"[!rcu_segcblist_segempty(&rdp->cblist, RCU_DONE_TAIL)]);
#ifdef CONFIG_RCU_BOOST
seq_printf(m, " kt=%d/%c ktl=%x",
per_cpu(rcu_cpu_has_work, rdp->cpu),
@@ -276,7 +275,9 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",
rsp->n_force_qs, rsp->n_force_qs_ngp,
rsp->n_force_qs - rsp->n_force_qs_ngp,
- READ_ONCE(rsp->n_force_qs_lh), rsp->qlen_lazy, rsp->qlen);
+ READ_ONCE(rsp->n_force_qs_lh),
+ rcu_cblist_n_lazy_cbs(&rsp->orphan_done),
+ rcu_cblist_n_cbs(&rsp->orphan_done));
for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < rcu_num_nodes; rnp++) {
if (rnp->level != level) {
seq_puts(m, "\n");
--
2.5.2