diff options
| -rw-r--r-- | include/linux/rcu_sync.h | 94 | ||||
| -rw-r--r-- | kernel/rcu/Makefile | 2 | ||||
| -rw-r--r-- | kernel/rcu/sync.c | 175 |
3 files changed, 270 insertions, 1 deletions
diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h new file mode 100644 index 000000000000..cb044df2e21c --- /dev/null +++ b/include/linux/rcu_sync.h @@ -0,0 +1,94 @@ +/* + * RCU-based infrastructure for lightweight reader-writer locking + * + * 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 (c) 2015, Red Hat, Inc. + * + * Author: Oleg Nesterov <oleg@redhat.com> + */ + +#ifndef _LINUX_RCU_SYNC_H_ +#define _LINUX_RCU_SYNC_H_ + +#include <linux/wait.h> +#include <linux/rcupdate.h> + +/* Structure to mediate between updaters and fastpath-using readers. */ +struct rcu_sync { + int gp_state; + int gp_count; + wait_queue_head_t gp_wait; + + int cb_state; + struct rcu_head cb_head; + + void (*sync)(void); + void (*call)(struct rcu_head *, void (*)(struct rcu_head *)); +}; + +#define ___RCU_SYNC_INIT(name) \ + .gp_state = 0, \ + .gp_count = 0, \ + .gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait), \ + .cb_state = 0 + +#define __RCU_SCHED_SYNC_INIT(name) { \ + ___RCU_SYNC_INIT(name), \ + .sync = synchronize_sched, \ + .call = call_rcu_sched, \ +} + +#define __RCU_BH_SYNC_INIT(name) { \ + ___RCU_SYNC_INIT(name), \ + .sync = synchronize_rcu_bh, \ + .call = call_rcu_bh, \ +} + +#define __RCU_SYNC_INIT(name) { \ + ___RCU_SYNC_INIT(name), \ + .sync = synchronize_rcu, \ + .call = call_rcu, \ +} + +#define DEFINE_RCU_SCHED_SYNC(name) \ + struct rcu_sync name = __RCU_SCHED_SYNC_INIT(name) + +#define DEFINE_RCU_BH_SYNC(name) \ + struct rcu_sync name = __RCU_BH_SYNC_INIT(name) + +#define DEFINE_RCU_SYNC(name) \ + struct rcu_sync name = __RCU_SYNC_INIT(name) + +/** + * rcu_sync_is_idle() - Are readers permitted to use their fastpaths? + * @rsp: Pointer to rcu_sync structure to use for synchronization + * + * Returns true if readers are permitted to use their fastpaths. + * Must be invoked within an RCU read-side critical section whose + * flavor matches that of the rcu_sync struture. + */ +static inline bool rcu_sync_is_idle(struct rcu_sync *rsp) +{ + return !rsp->gp_state; /* GP_IDLE */ +} + +enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC }; + +extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type); +extern void rcu_sync_enter(struct rcu_sync *); +extern void rcu_sync_exit(struct rcu_sync *); + +#endif /* _LINUX_RCU_SYNC_H_ */ diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile index 50a808424b06..61a16569ffbf 100644 --- a/kernel/rcu/Makefile +++ b/kernel/rcu/Makefile @@ -1,4 +1,4 @@ -obj-y += update.o +obj-y += update.o sync.o obj-$(CONFIG_SRCU) += srcu.o obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o obj-$(CONFIG_TREE_RCU) += tree.o diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c new file mode 100644 index 000000000000..0a11df43be23 --- /dev/null +++ b/kernel/rcu/sync.c @@ -0,0 +1,175 @@ +/* + * RCU-based infrastructure for lightweight reader-writer locking + * + * 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 (c) 2015, Red Hat, Inc. + * + * Author: Oleg Nesterov <oleg@redhat.com> + */ + +#include <linux/rcu_sync.h> +#include <linux/sched.h> + +enum { GP_IDLE = 0, GP_PENDING, GP_PASSED }; +enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY }; + +#define rss_lock gp_wait.lock + +/** + * rcu_sync_init() - Initialize an rcu_sync structure + * @rsp: Pointer to rcu_sync structure to be initialized + * @type: Flavor of RCU with which to synchronize rcu_sync structure + */ +void rcu_sync_init(struct rcu_sync *rsp, enum rcu_sync_type type) +{ + memset(rsp, 0, sizeof(*rsp)); + init_waitqueue_head(&rsp->gp_wait); + + switch (type) { + case RCU_SYNC: + rsp->sync = synchronize_rcu; + rsp->call = call_rcu; + break; + + case RCU_SCHED_SYNC: + rsp->sync = synchronize_sched; + rsp->call = call_rcu_sched; + break; + + case RCU_BH_SYNC: + rsp->sync = synchronize_rcu_bh; + rsp->call = call_rcu_bh; + break; + } +} + +/** + * rcu_sync_enter() - Force readers onto slowpath + * @rsp: Pointer to rcu_sync structure to use for synchronization + * + * This function is used by updaters who need readers to make use of + * a slowpath during the update. After this function returns, all + * subsequent calls to rcu_sync_is_idle() will return false, which + * tells readers to stay off their fastpaths. A later call to + * rcu_sync_exit() re-enables reader slowpaths. + * + * When called in isolation, rcu_sync_enter() must wait for a grace + * period, however, closely spaced calls to rcu_sync_enter() can + * optimize away the grace-period wait via a state machine implemented + * by rcu_sync_enter(), rcu_sync_exit(), and rcu_sync_func(). + */ +void rcu_sync_enter(struct rcu_sync *rsp) +{ + bool need_wait, need_sync; + + spin_lock_irq(&rsp->rss_lock); + need_wait = rsp->gp_count++; + need_sync = rsp->gp_state == GP_IDLE; + if (need_sync) + rsp->gp_state = GP_PENDING; + spin_unlock_irq(&rsp->rss_lock); + + BUG_ON(need_wait && need_sync); + + if (need_sync) { + rsp->sync(); + rsp->gp_state = GP_PASSED; + wake_up_all(&rsp->gp_wait); + } else if (need_wait) { + wait_event(rsp->gp_wait, rsp->gp_state == GP_PASSED); + } else { + /* + * Possible when there's a pending CB from a rcu_sync_exit(). + * Nobody has yet been allowed the 'fast' path and thus we can + * avoid doing any sync(). The callback will get 'dropped'. + */ + BUG_ON(rsp->gp_state != GP_PASSED); + } +} + +/** + * rcu_sync_func() - Callback function managing reader access to fastpath + * @rsp: Pointer to rcu_sync structure to use for synchronization + * + * This function is passed to one of the call_rcu() functions by + * rcu_sync_exit(), so that it is invoked after a grace period following the + * that invocation of rcu_sync_exit(). It takes action based on events that + * have taken place in the meantime, so that closely spaced rcu_sync_enter() + * and rcu_sync_exit() pairs need not wait for a grace period. + * + * If another rcu_sync_enter() is invoked before the grace period + * ended, reset state to allow the next rcu_sync_exit() to let the + * readers back onto their fastpaths (after a grace period). If both + * another rcu_sync_enter() and its matching rcu_sync_exit() are invoked + * before the grace period ended, re-invoke call_rcu() on behalf of that + * rcu_sync_exit(). Otherwise, set all state back to idle so that readers + * can again use their fastpaths. + */ +static void rcu_sync_func(struct rcu_head *rcu) +{ + struct rcu_sync *rsp = container_of(rcu, struct rcu_sync, cb_head); + unsigned long flags; + + BUG_ON(rsp->gp_state != GP_PASSED); + BUG_ON(rsp->cb_state == CB_IDLE); + + spin_lock_irqsave(&rsp->rss_lock, flags); + if (rsp->gp_count) { + /* + * A new rcu_sync_begin() has happened; drop the callback. + */ + rsp->cb_state = CB_IDLE; + } else if (rsp->cb_state == CB_REPLAY) { + /* + * A new rcu_sync_exit() has happened; requeue the callback + * to catch a later GP. + */ + rsp->cb_state = CB_PENDING; + rsp->call(&rsp->cb_head, rcu_sync_func); + } else { + /* + * We're at least a GP after rcu_sync_exit(); eveybody will now + * have observed the write side critical section. Let 'em rip!. + */ + rsp->cb_state = CB_IDLE; + rsp->gp_state = GP_IDLE; + } + spin_unlock_irqrestore(&rsp->rss_lock, flags); +} + +/** + * rcu_sync_exit() - Allow readers back onto fast patch after grace period + * @rsp: Pointer to rcu_sync structure to use for synchronization + * + * This function is used by updaters who have completed, and can therefore + * now allow readers to make use of their fastpaths after a grace period + * has elapsed. After this grace period has completed, all subsequent + * calls to rcu_sync_is_idle() will return true, which tells readers that + * they can once again use their fastpaths. + */ +void rcu_sync_exit(struct rcu_sync *rsp) +{ + spin_lock_irq(&rsp->rss_lock); + if (!--rsp->gp_count) { + if (rsp->cb_state == CB_IDLE) { + rsp->cb_state = CB_PENDING; + rsp->call(&rsp->cb_head, rcu_sync_func); + } else if (rsp->cb_state == CB_PENDING) { + rsp->cb_state = CB_REPLAY; + } + } + spin_unlock_irq(&rsp->rss_lock); +} |