diff options
| -rw-r--r-- | init/Kconfig | 3 | ||||
| -rw-r--r-- | kernel/rcu/Makefile | 1 | ||||
| -rw-r--r-- | kernel/rcu/rcu_segcblist.c | 505 | ||||
| -rw-r--r-- | kernel/rcu/rcu_segcblist.h | 533 |
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); |