| /* |
| * 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 IBM Corporation, 2001 |
| * |
| * Author: Dipankar Sarma <dipankar@in.ibm.com> |
| * |
| * Based on the original work by Paul McKenney <paulmck@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> |
| #include <linux/lockdep.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); |
| }; |
| |
| #include <linux/rcuclassic.h> |
| |
| #define RCU_HEAD_INIT { .next = NULL, .func = NULL } |
| #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT |
| #define INIT_RCU_HEAD(ptr) do { \ |
| (ptr)->next = NULL; (ptr)->func = NULL; \ |
| } while (0) |
| |
| /** |
| * rcu_read_lock - mark the beginning of an RCU read-side critical section. |
| * |
| * When synchronize_rcu() is invoked on one CPU while other CPUs |
| * are within RCU read-side critical sections, then the |
| * synchronize_rcu() 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() __rcu_read_lock() |
| |
| /** |
| * rcu_read_unlock - marks the end of an RCU read-side critical section. |
| * |
| * See rcu_read_lock() for more information. |
| */ |
| |
| /* |
| * 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. |
| */ |
| #define rcu_read_unlock() __rcu_read_unlock() |
| |
| /** |
| * 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() __rcu_read_lock_bh() |
| |
| /* |
| * 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() __rcu_read_unlock_bh() |
| |
| /* |
| * Prevent the compiler from merging or refetching accesses. The compiler |
| * is also forbidden from reordering successive instances of ACCESS_ONCE(), |
| * but only when the compiler is aware of some particular ordering. One way |
| * to make the compiler aware of ordering is to put the two invocations of |
| * ACCESS_ONCE() in different C statements. |
| * |
| * This macro does absolutely -nothing- to prevent the CPU from reordering, |
| * merging, or refetching absolutely anything at any time. |
| */ |
| #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) |
| |
| /** |
| * 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 = ACCESS_ONCE(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); \ |
| }) |
| |
| /** |
| * synchronize_sched - block until all CPUs have exited any non-preemptive |
| * kernel code sequences. |
| * |
| * This means that all preempt_disable code sequences, including NMI and |
| * hardware-interrupt handlers, in progress on entry will have completed |
| * before this primitive returns. However, this does not guarantee that |
| * softirq handlers will have completed, since in some kernels, these |
| * handlers can run in process context, and can block. |
| * |
| * This primitive provides the guarantees made by the (now removed) |
| * synchronize_kernel() API. In contrast, synchronize_rcu() only |
| * guarantees that rcu_read_lock() sections will have completed. |
| * In "classic RCU", these two guarantees happen to be one and |
| * the same, but can differ in realtime RCU implementations. |
| */ |
| #define synchronize_sched() __synchronize_sched() |
| |
| /** |
| * call_rcu - Queue an RCU callback for invocation after a grace period. |
| * @head: structure to be used for queueing the RCU updates. |
| * @func: actual update function to be invoked after the grace period |
| * |
| * The update function will be invoked some time after a full grace |
| * period elapses, in other words after all currently executing RCU |
| * read-side critical sections have completed. RCU read-side critical |
| * sections are delimited by rcu_read_lock() and rcu_read_unlock(), |
| * and may be nested. |
| */ |
| extern void call_rcu(struct rcu_head *head, |
| void (*func)(struct rcu_head *head)); |
| |
| /** |
| * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. |
| * @head: structure to be used for queueing the RCU updates. |
| * @func: actual update function to be invoked after the grace period |
| * |
| * The update function will be invoked some time after a full grace |
| * period elapses, in other words after all currently executing RCU |
| * read-side critical sections have completed. call_rcu_bh() assumes |
| * that the read-side critical sections end on completion of a softirq |
| * handler. This means that read-side critical sections in process |
| * context must not be interrupted by softirqs. This interface is to be |
| * used when most of the read-side critical sections are in softirq context. |
| * RCU read-side critical sections are delimited by : |
| * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. |
| * OR |
| * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. |
| * These may be nested. |
| */ |
| extern void call_rcu_bh(struct rcu_head *head, |
| void (*func)(struct rcu_head *head)); |
| |
| /* Exported common interfaces */ |
| extern void synchronize_rcu(void); |
| extern void rcu_barrier(void); |
| |
| /* Internal to kernel */ |
| extern void rcu_init(void); |
| extern void rcu_check_callbacks(int cpu, int user); |
| |
| extern long rcu_batches_completed(void); |
| extern long rcu_batches_completed_bh(void); |
| |
| #endif /* __KERNEL__ */ |
| #endif /* __LINUX_RCUPDATE_H */ |