/* * Sleepable 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, 2006 * * Author: Paul McKenney * * For detailed explanation of Read-Copy Update mechanism see - * Documentation/RCU/ *.txt * */ #ifndef _LINUX_SRCU_H #define _LINUX_SRCU_H #include #include struct srcu_struct_array { unsigned long c[2]; unsigned long seq[2]; }; struct srcu_struct { unsigned completed; struct srcu_struct_array __percpu *per_cpu_ref; struct mutex mutex; #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ }; #ifdef CONFIG_DEBUG_LOCK_ALLOC int __init_srcu_struct(struct srcu_struct *sp, const char *name, struct lock_class_key *key); #define init_srcu_struct(sp) \ ({ \ static struct lock_class_key __srcu_key; \ \ __init_srcu_struct((sp), #sp, &__srcu_key); \ }) #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ int init_srcu_struct(struct srcu_struct *sp); #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ void cleanup_srcu_struct(struct srcu_struct *sp); int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp); void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp); void synchronize_srcu(struct srcu_struct *sp); void synchronize_srcu_expedited(struct srcu_struct *sp); long srcu_batches_completed(struct srcu_struct *sp); #ifdef CONFIG_DEBUG_LOCK_ALLOC /** * srcu_read_lock_held - might we be in SRCU read-side critical section? * * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, * this assumes we are in an SRCU read-side critical section unless it can * prove otherwise. * * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot * and while lockdep is disabled. * * Note that if the CPU is in the idle loop from an RCU point of view * (ie: that we are in the section between rcu_idle_enter() and * rcu_idle_exit()) then srcu_read_lock_held() returns false even if * the CPU did an srcu_read_lock(). The reason for this is that RCU * ignores CPUs that are in such a section, considering these as in * extended quiescent state, so such a CPU is effectively never in an * RCU read-side critical section regardless of what RCU primitives it * invokes. This state of affairs is required --- we need to keep an * RCU-free window in idle where the CPU may possibly enter into low * power mode. This way we can notice an extended quiescent state to * other CPUs that started a grace period. Otherwise we would delay any * grace period as long as we run in the idle task. * * Similarly, we avoid claiming an SRCU read lock held if the current * CPU is offline. */ static inline int srcu_read_lock_held(struct srcu_struct *sp) { if (!debug_lockdep_rcu_enabled()) return 1; if (rcu_is_cpu_idle()) return 0; if (!rcu_lockdep_current_cpu_online()) return 0; return lock_is_held(&sp->dep_map); } #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ static inline int srcu_read_lock_held(struct srcu_struct *sp) { return 1; } #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ /** * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing * @p: the pointer to fetch and protect for later dereferencing * @sp: pointer to the srcu_struct, which is used to check that we * really are in an SRCU read-side critical section. * @c: condition to check for update-side use * * If PROVE_RCU is enabled, invoking this outside of an RCU read-side * critical section will result in an RCU-lockdep splat, unless @c evaluates * to 1. The @c argument will normally be a logical expression containing * lockdep_is_held() calls. */ #define srcu_dereference_check(p, sp, c) \ __rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu) /** * srcu_dereference - fetch SRCU-protected pointer for later dereferencing * @p: the pointer to fetch and protect for later dereferencing * @sp: pointer to the srcu_struct, which is used to check that we * really are in an SRCU read-side critical section. * * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU * is enabled, invoking this outside of an RCU read-side critical * section will result in an RCU-lockdep splat. */ #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0) /** * srcu_read_lock - register a new reader for an SRCU-protected structure. * @sp: srcu_struct in which to register the new reader. * * Enter an SRCU read-side critical section. Note that SRCU read-side * critical sections may be nested. However, it is illegal to * call anything that waits on an SRCU grace period for the same * srcu_struct, whether directly or indirectly. Please note that * one way to indirectly wait on an SRCU grace period is to acquire * a mutex that is held elsewhere while calling synchronize_srcu() or * synchronize_srcu_expedited(). * * Note that srcu_read_lock() and the matching srcu_read_unlock() must * occur in the same context, for example, it is illegal to invoke * srcu_read_unlock() in an irq handler if the matching srcu_read_lock() * was invoked in process context. */ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) { int retval = __srcu_read_lock(sp); rcu_lock_acquire(&(sp)->dep_map); rcu_lockdep_assert(!rcu_is_cpu_idle(), "srcu_read_lock() used illegally while idle"); return retval; } /** * srcu_read_unlock - unregister a old reader from an SRCU-protected structure. * @sp: srcu_struct in which to unregister the old reader. * @idx: return value from corresponding srcu_read_lock(). * * Exit an SRCU read-side critical section. */ static inline void srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp) { rcu_lockdep_assert(!rcu_is_cpu_idle(), "srcu_read_unlock() used illegally while idle"); rcu_lock_release(&(sp)->dep_map); __srcu_read_unlock(sp, idx); } /** * srcu_read_lock_raw - register a new reader for an SRCU-protected structure. * @sp: srcu_struct in which to register the new reader. * * Enter an SRCU read-side critical section. Similar to srcu_read_lock(), * but avoids the RCU-lockdep checking. This means that it is legal to * use srcu_read_lock_raw() in one context, for example, in an exception * handler, and then have the matching srcu_read_unlock_raw() in another * context, for example in the task that took the exception. * * However, the entire SRCU read-side critical section must reside within a * single task. For example, beware of using srcu_read_lock_raw() in * a device interrupt handler and srcu_read_unlock() in the interrupted * task: This will not work if interrupts are threaded. */ static inline int srcu_read_lock_raw(struct srcu_struct *sp) { unsigned long flags; int ret; local_irq_save(flags); ret = __srcu_read_lock(sp); local_irq_restore(flags); return ret; } /** * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure. * @sp: srcu_struct in which to unregister the old reader. * @idx: return value from corresponding srcu_read_lock_raw(). * * Exit an SRCU read-side critical section without lockdep-RCU checking. * See srcu_read_lock_raw() for more details. */ static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx) { unsigned long flags; local_irq_save(flags); __srcu_read_unlock(sp, idx); local_irq_restore(flags); } #endif