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Diffstat (limited to 'include/linux/rcupdate.h')
| -rw-r--r-- | include/linux/rcupdate.h | 271 |
1 files changed, 271 insertions, 0 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h new file mode 100644 index 000000000000..4d747433916b --- /dev/null +++ b/include/linux/rcupdate.h @@ -0,0 +1,271 @@ +/* + * Read-Copy Update mechanism for mutual exclusion + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * + * Copyright (C) IBM Corporation, 2001 + * + * Author: Dipankar Sarma <dipankar@in.ibm.com> + * + * Based on the original work by Paul McKenney <paul.mckenney@us.ibm.com> + * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. + * Papers: + * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf + * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) + * + * For detailed explanation of Read-Copy Update mechanism see - + * http://lse.sourceforge.net/locking/rcupdate.html + * + */ + +#ifndef __LINUX_RCUPDATE_H +#define __LINUX_RCUPDATE_H + +#ifdef __KERNEL__ + +#include <linux/cache.h> +#include <linux/spinlock.h> +#include <linux/threads.h> +#include <linux/percpu.h> +#include <linux/cpumask.h> +#include <linux/seqlock.h> + +/** + * struct rcu_head - callback structure for use with RCU + * @next: next update requests in a list + * @func: actual update function to call after the grace period. + */ +struct rcu_head { + struct rcu_head *next; + void (*func)(struct rcu_head *head); +}; + +#define RCU_HEAD_INIT(head) { .next = NULL, .func = NULL } +#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT(head) +#define INIT_RCU_HEAD(ptr) do { \ + (ptr)->next = NULL; (ptr)->func = NULL; \ +} while (0) + + + +/* Global control variables for rcupdate callback mechanism. */ +struct rcu_ctrlblk { + long cur; /* Current batch number. */ + long completed; /* Number of the last completed batch */ + int next_pending; /* Is the next batch already waiting? */ +} ____cacheline_maxaligned_in_smp; + +/* Is batch a before batch b ? */ +static inline int rcu_batch_before(long a, long b) +{ + return (a - b) < 0; +} + +/* Is batch a after batch b ? */ +static inline int rcu_batch_after(long a, long b) +{ + return (a - b) > 0; +} + +/* + * Per-CPU data for Read-Copy UPdate. + * nxtlist - new callbacks are added here + * curlist - current batch for which quiescent cycle started if any + */ +struct rcu_data { + /* 1) quiescent state handling : */ + long quiescbatch; /* Batch # for grace period */ + int passed_quiesc; /* User-mode/idle loop etc. */ + int qs_pending; /* core waits for quiesc state */ + + /* 2) batch handling */ + long batch; /* Batch # for current RCU batch */ + struct rcu_head *nxtlist; + struct rcu_head **nxttail; + struct rcu_head *curlist; + struct rcu_head **curtail; + struct rcu_head *donelist; + struct rcu_head **donetail; + int cpu; +}; + +DECLARE_PER_CPU(struct rcu_data, rcu_data); +DECLARE_PER_CPU(struct rcu_data, rcu_bh_data); +extern struct rcu_ctrlblk rcu_ctrlblk; +extern struct rcu_ctrlblk rcu_bh_ctrlblk; + +/* + * Increment the quiescent state counter. + * The counter is a bit degenerated: We do not need to know + * how many quiescent states passed, just if there was at least + * one since the start of the grace period. Thus just a flag. + */ +static inline void rcu_qsctr_inc(int cpu) +{ + struct rcu_data *rdp = &per_cpu(rcu_data, cpu); + rdp->passed_quiesc = 1; +} +static inline void rcu_bh_qsctr_inc(int cpu) +{ + struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu); + rdp->passed_quiesc = 1; +} + +static inline int __rcu_pending(struct rcu_ctrlblk *rcp, + struct rcu_data *rdp) +{ + /* This cpu has pending rcu entries and the grace period + * for them has completed. + */ + if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) + return 1; + + /* This cpu has no pending entries, but there are new entries */ + if (!rdp->curlist && rdp->nxtlist) + return 1; + + /* This cpu has finished callbacks to invoke */ + if (rdp->donelist) + return 1; + + /* The rcu core waits for a quiescent state from the cpu */ + if (rdp->quiescbatch != rcp->cur || rdp->qs_pending) + return 1; + + /* nothing to do */ + return 0; +} + +static inline int rcu_pending(int cpu) +{ + return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) || + __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu)); +} + +/** + * rcu_read_lock - mark the beginning of an RCU read-side critical section. + * + * When synchronize_kernel() is invoked on one CPU while other CPUs + * are within RCU read-side critical sections, then the + * synchronize_kernel() is guaranteed to block until after all the other + * CPUs exit their critical sections. Similarly, if call_rcu() is invoked + * on one CPU while other CPUs are within RCU read-side critical + * sections, invocation of the corresponding RCU callback is deferred + * until after the all the other CPUs exit their critical sections. + * + * Note, however, that RCU callbacks are permitted to run concurrently + * with RCU read-side critical sections. One way that this can happen + * is via the following sequence of events: (1) CPU 0 enters an RCU + * read-side critical section, (2) CPU 1 invokes call_rcu() to register + * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, + * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU + * callback is invoked. This is legal, because the RCU read-side critical + * section that was running concurrently with the call_rcu() (and which + * therefore might be referencing something that the corresponding RCU + * callback would free up) has completed before the corresponding + * RCU callback is invoked. + * + * RCU read-side critical sections may be nested. Any deferred actions + * will be deferred until the outermost RCU read-side critical section + * completes. + * + * It is illegal to block while in an RCU read-side critical section. + */ +#define rcu_read_lock() preempt_disable() + +/** + * rcu_read_unlock - marks the end of an RCU read-side critical section. + * + * See rcu_read_lock() for more information. + */ +#define rcu_read_unlock() preempt_enable() + +/* + * So where is rcu_write_lock()? It does not exist, as there is no + * way for writers to lock out RCU readers. This is a feature, not + * a bug -- this property is what provides RCU's performance benefits. + * Of course, writers must coordinate with each other. The normal + * spinlock primitives work well for this, but any other technique may be + * used as well. RCU does not care how the writers keep out of each + * others' way, as long as they do so. + */ + +/** + * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section + * + * This is equivalent of rcu_read_lock(), but to be used when updates + * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks + * consider completion of a softirq handler to be a quiescent state, + * a process in RCU read-side critical section must be protected by + * disabling softirqs. Read-side critical sections in interrupt context + * can use just rcu_read_lock(). + * + */ +#define rcu_read_lock_bh() local_bh_disable() + +/* + * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section + * + * See rcu_read_lock_bh() for more information. + */ +#define rcu_read_unlock_bh() local_bh_enable() + +/** + * rcu_dereference - fetch an RCU-protected pointer in an + * RCU read-side critical section. This pointer may later + * be safely dereferenced. + * + * Inserts memory barriers on architectures that require them + * (currently only the Alpha), and, more importantly, documents + * exactly which pointers are protected by RCU. + */ + +#define rcu_dereference(p) ({ \ + typeof(p) _________p1 = p; \ + smp_read_barrier_depends(); \ + (_________p1); \ + }) + +/** + * rcu_assign_pointer - assign (publicize) a pointer to a newly + * initialized structure that will be dereferenced by RCU read-side + * critical sections. Returns the value assigned. + * + * Inserts memory barriers on architectures that require them + * (pretty much all of them other than x86), and also prevents + * the compiler from reordering the code that initializes the + * structure after the pointer assignment. More importantly, this + * call documents which pointers will be dereferenced by RCU read-side + * code. + */ + +#define rcu_assign_pointer(p, v) ({ \ + smp_wmb(); \ + (p) = (v); \ + }) + +extern void rcu_init(void); +extern void rcu_check_callbacks(int cpu, int user); +extern void rcu_restart_cpu(int cpu); + +/* Exported interfaces */ +extern void FASTCALL(call_rcu(struct rcu_head *head, + void (*func)(struct rcu_head *head))); +extern void FASTCALL(call_rcu_bh(struct rcu_head *head, + void (*func)(struct rcu_head *head))); +extern void synchronize_kernel(void); + +#endif /* __KERNEL__ */ +#endif /* __LINUX_RCUPDATE_H */ |