Edit File: rcupdate.h
/* * 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 #include <linux/types.h> #include <linux/cache.h> #include <linux/spinlock.h> #include <linux/threads.h> #include <linux/cpumask.h> #include <linux/seqlock.h> #include <linux/lockdep.h> #include <linux/completion.h> #include <linux/debugobjects.h> #include <linux/bug.h> #include <linux/compiler.h> #ifdef CONFIG_RCU_TORTURE_TEST extern int rcutorture_runnable; /* for sysctl */ #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) extern void rcutorture_record_test_transition(void); extern void rcutorture_record_progress(unsigned long vernum); extern void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp, unsigned long secs, unsigned long c_old, unsigned long c); #else static inline void rcutorture_record_test_transition(void) { } static inline void rcutorture_record_progress(unsigned long vernum) { } #ifdef CONFIG_RCU_TRACE extern void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp, unsigned long secs, unsigned long c_old, unsigned long c); #else #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ do { } while (0) #endif #endif #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) #define ulong2long(a) (*(long *)(&(a))) /* Exported common interfaces */ #ifdef CONFIG_PREEMPT_RCU /** * call_rcu() - Queue an RCU callback for invocation after a grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual callback function to be invoked after the grace period * * The callback function will be invoked some time after a full grace * period elapses, in other words after all pre-existing RCU read-side * critical sections have completed. However, the callback function * might well execute concurrently with RCU read-side critical sections * that started after call_rcu() was invoked. RCU read-side critical * sections are delimited by rcu_read_lock() and rcu_read_unlock(), * and may be nested. * * Note that all CPUs must agree that the grace period extended beyond * all pre-existing RCU read-side critical section. On systems with more * than one CPU, this means that when "func()" is invoked, each CPU is * guaranteed to have executed a full memory barrier since the end of its * last RCU read-side critical section whose beginning preceded the call * to call_rcu(). It also means that each CPU executing an RCU read-side * critical section that continues beyond the start of "func()" must have * executed a memory barrier after the call_rcu() but before the beginning * of that RCU read-side critical section. Note that these guarantees * include CPUs that are offline, idle, or executing in user mode, as * well as CPUs that are executing in the kernel. * * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the * resulting RCU callback function "func()", then both CPU A and CPU B are * guaranteed to execute a full memory barrier during the time interval * between the call to call_rcu() and the invocation of "func()" -- even * if CPU A and CPU B are the same CPU (but again only if the system has * more than one CPU). */ extern void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *head)); #else /* #ifdef CONFIG_PREEMPT_RCU */ /* In classic RCU, call_rcu() is just call_rcu_sched(). */ #define call_rcu call_rcu_sched #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ /** * 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 callback function to be invoked after the grace period * * The callback 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. * * See the description of call_rcu() for more detailed information on * memory ordering guarantees. */ extern void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *head)); /** * call_rcu_sched() - Queue an RCU for invocation after sched grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual callback function to be invoked after the grace period * * The callback 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_sched() assumes * that the read-side critical sections end on enabling of preemption * or on voluntary preemption. * RCU read-side critical sections are delimited by : * - rcu_read_lock_sched() and rcu_read_unlock_sched(), * OR * anything that disables preemption. * These may be nested. * * See the description of call_rcu() for more detailed information on * memory ordering guarantees. */ extern void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)); extern void synchronize_sched(void); #ifdef CONFIG_PREEMPT_RCU extern void __rcu_read_lock(void); extern void __rcu_read_unlock(void); extern void rcu_read_unlock_special(struct task_struct *t); void synchronize_rcu(void); /* * Defined as a macro as it is a very low level header included from * areas that don't even know about current. This gives the rcu_read_lock() * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. */ #define rcu_preempt_depth() (current->rcu_read_lock_nesting) #else /* #ifdef CONFIG_PREEMPT_RCU */ static inline void __rcu_read_lock(void) { preempt_disable(); } static inline void __rcu_read_unlock(void) { preempt_enable(); } static inline void synchronize_rcu(void) { synchronize_sched(); } static inline int rcu_preempt_depth(void) { return 0; } #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ /* Internal to kernel */ extern void rcu_sched_qs(int cpu); extern void rcu_bh_qs(int cpu); extern void rcu_check_callbacks(int cpu, int user); struct notifier_block; extern void rcu_idle_enter(void); extern void rcu_idle_exit(void); extern void rcu_irq_enter(void); extern void rcu_irq_exit(void); #ifdef CONFIG_RCU_STALL_COMMON void rcu_sysrq_start(void); void rcu_sysrq_end(void); #else /* #ifdef CONFIG_RCU_STALL_COMMON */ static inline void rcu_sysrq_start(void) { } static inline void rcu_sysrq_end(void) { } #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */ #ifdef CONFIG_RCU_USER_QS extern void rcu_user_enter(void); extern void rcu_user_exit(void); extern void rcu_user_enter_after_irq(void); extern void rcu_user_exit_after_irq(void); #else static inline void rcu_user_enter(void) { } static inline void rcu_user_exit(void) { } static inline void rcu_user_enter_after_irq(void) { } static inline void rcu_user_exit_after_irq(void) { } static inline void rcu_user_hooks_switch(struct task_struct *prev, struct task_struct *next) { } #endif /* CONFIG_RCU_USER_QS */ extern void exit_rcu(void); #ifdef CONFIG_RCU_NOCB_CPU void rcu_init_nohz(void); #else /* #ifdef CONFIG_RCU_NOCB_CPU */ static inline void rcu_init_nohz(void) { } #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ /** * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers * @a: Code that RCU needs to pay attention to. * * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden * in the inner idle loop, that is, between the rcu_idle_enter() and * the rcu_idle_exit() -- RCU will happily ignore any such read-side * critical sections. However, things like powertop need tracepoints * in the inner idle loop. * * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) * will tell RCU that it needs to pay attending, invoke its argument * (in this example, a call to the do_something_with_RCU() function), * and then tell RCU to go back to ignoring this CPU. It is permissible * to nest RCU_NONIDLE() wrappers, but the nesting level is currently * quite limited. If deeper nesting is required, it will be necessary * to adjust DYNTICK_TASK_NESTING_VALUE accordingly. */ #define RCU_NONIDLE(a) \ do { \ rcu_irq_enter(); \ do { a; } while (0); \ rcu_irq_exit(); \ } while (0) #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) extern bool __rcu_is_watching(void); #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */ /* * Infrastructure to implement the synchronize_() primitives in * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. */ typedef void call_rcu_func_t(struct rcu_head *head, void (*func)(struct rcu_head *head)); void wait_rcu_gp(call_rcu_func_t crf); #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) #include <linux/rcutree.h> #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) #include <linux/rcutiny.h> #else #error "Unknown RCU implementation specified to kernel configuration" #endif /* * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic * initialization and destruction of rcu_head on the stack. rcu_head structures * allocated dynamically in the heap or defined statically don't need any * initialization. */ #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD void init_rcu_head(struct rcu_head *head); void destroy_rcu_head(struct rcu_head *head); void init_rcu_head_on_stack(struct rcu_head *head); void destroy_rcu_head_on_stack(struct rcu_head *head); #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ static inline void init_rcu_head(struct rcu_head *head) { } static inline void destroy_rcu_head(struct rcu_head *head) { } static inline void init_rcu_head_on_stack(struct rcu_head *head) { } static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { } #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) bool rcu_lockdep_current_cpu_online(void); #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ static inline bool rcu_lockdep_current_cpu_online(void) { return 1; } #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ #ifdef CONFIG_DEBUG_LOCK_ALLOC static inline void rcu_lock_acquire(struct lockdep_map *map) { lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_); } static inline void rcu_lock_release(struct lockdep_map *map) { lock_release(map, 1, _THIS_IP_); } extern struct lockdep_map rcu_lock_map; extern struct lockdep_map rcu_bh_lock_map; extern struct lockdep_map rcu_sched_lock_map; extern int debug_lockdep_rcu_enabled(void); /** * rcu_read_lock_held() - might we be in RCU read-side critical section? * * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, * this assumes we are in an RCU read-side critical section unless it can * prove otherwise. This is useful for debug checks in functions that * require that they be called within an RCU read-side critical section. * * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot * and while lockdep is disabled. * * Note that rcu_read_lock() and the matching rcu_read_unlock() must * occur in the same context, for example, it is illegal to invoke * rcu_read_unlock() in process context if the matching rcu_read_lock() * was invoked from within an irq handler. * * Note that rcu_read_lock() is disallowed if the CPU is either idle or * offline from an RCU perspective, so check for those as well. */ static inline int rcu_read_lock_held(void) { if (!debug_lockdep_rcu_enabled()) return 1; if (!rcu_is_watching()) return 0; if (!rcu_lockdep_current_cpu_online()) return 0; return lock_is_held(&rcu_lock_map); } /* * rcu_read_lock_bh_held() is defined out of line to avoid #include-file * hell. */ extern int rcu_read_lock_bh_held(void); /** * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? * * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an * RCU-sched read-side critical section. In absence of * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side * critical section unless it can prove otherwise. Note that disabling * of preemption (including disabling irqs) counts as an RCU-sched * read-side critical section. This is useful for debug checks in functions * that required that they be called within an RCU-sched read-side * critical section. * * Check 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 rcu_read_lock_held() returns false even if the CPU * did an rcu_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. */ #ifdef CONFIG_PREEMPT_COUNT static inline int rcu_read_lock_sched_held(void) { int lockdep_opinion = 0; if (!debug_lockdep_rcu_enabled()) return 1; if (!rcu_is_watching()) return 0; if (!rcu_lockdep_current_cpu_online()) return 0; if (debug_locks) lockdep_opinion = lock_is_held(&rcu_sched_lock_map); return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); } #else /* #ifdef CONFIG_PREEMPT_COUNT */ static inline int rcu_read_lock_sched_held(void) { return 1; } #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ # define rcu_lock_acquire(a) do { } while (0) # define rcu_lock_release(a) do { } while (0) static inline int rcu_read_lock_held(void) { return 1; } static inline int rcu_read_lock_bh_held(void) { return 1; } #ifdef CONFIG_PREEMPT_COUNT static inline int rcu_read_lock_sched_held(void) { return preempt_count() != 0 || irqs_disabled(); } #else /* #ifdef CONFIG_PREEMPT_COUNT */ static inline int rcu_read_lock_sched_held(void) { return 1; } #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ #ifdef CONFIG_PROVE_RCU /** * rcu_lockdep_assert - emit lockdep splat if specified condition not met * @c: condition to check * @s: informative message */ #define rcu_lockdep_assert(c, s) \ do { \ static bool __section(.data.unlikely) __warned; \ if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ __warned = true; \ lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ } \ } while (0) #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) static inline void rcu_preempt_sleep_check(void) { rcu_lockdep_assert(!lock_is_held(&rcu_lock_map), "Illegal context switch in RCU read-side critical section"); } #else /* #ifdef CONFIG_PROVE_RCU */ static inline void rcu_preempt_sleep_check(void) { } #endif /* #else #ifdef CONFIG_PROVE_RCU */ #define rcu_sleep_check() \ do { \ rcu_preempt_sleep_check(); \ rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \ "Illegal context switch in RCU-bh" \ " read-side critical section"); \ rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \ "Illegal context switch in RCU-sched"\ " read-side critical section"); \ } while (0) #else /* #ifdef CONFIG_PROVE_RCU */ #define rcu_lockdep_assert(c, s) do { } while (0) #define rcu_sleep_check() do { } while (0) #endif /* #else #ifdef CONFIG_PROVE_RCU */ /* * Helper functions for rcu_dereference_check(), rcu_dereference_protected() * and rcu_assign_pointer(). Some of these could be folded into their * callers, but they are left separate in order to ease introduction of * multiple flavors of pointers to match the multiple flavors of RCU * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in * the future. */ #ifdef __CHECKER__ #define rcu_dereference_sparse(p, space) \ ((void)(((typeof(*p) space *)p) == p)) #else /* #ifdef __CHECKER__ */ #define rcu_dereference_sparse(p, space) #endif /* #else #ifdef __CHECKER__ */ #define __rcu_access_pointer(p, space) \ ({ \ typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ rcu_dereference_sparse(p, space); \ ((typeof(*p) __force __kernel *)(_________p1)); \ }) #define __rcu_dereference_check(p, c, space) \ ({ \ typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \ " usage"); \ rcu_dereference_sparse(p, space); \ smp_read_barrier_depends(); \ ((typeof(*p) __force __kernel *)(_________p1)); \ }) #define __rcu_dereference_protected(p, c, space) \ ({ \ rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \ " usage"); \ rcu_dereference_sparse(p, space); \ ((typeof(*p) __force __kernel *)(p)); \ }) #define __rcu_access_index(p, space) \ ({ \ typeof(p) _________p1 = ACCESS_ONCE(p); \ rcu_dereference_sparse(p, space); \ (_________p1); \ }) #define __rcu_dereference_index_check(p, c) \ ({ \ typeof(p) _________p1 = ACCESS_ONCE(p); \ rcu_lockdep_assert(c, \ "suspicious rcu_dereference_index_check()" \ " usage"); \ smp_read_barrier_depends(); \ (_________p1); \ }) #define __rcu_assign_pointer(p, v, space) \ do { \ smp_wmb(); \ (p) = (typeof(*v) __force space *)(v); \ } while (0) /** * rcu_access_pointer() - fetch RCU pointer with no dereferencing * @p: The pointer to read * * Return the value of the specified RCU-protected pointer, but omit the * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful * when the value of this pointer is accessed, but the pointer is not * dereferenced, for example, when testing an RCU-protected pointer against * NULL. Although rcu_access_pointer() may also be used in cases where * update-side locks prevent the value of the pointer from changing, you * should instead use rcu_dereference_protected() for this use case. * * It is also permissible to use rcu_access_pointer() when read-side * access to the pointer was removed at least one grace period ago, as * is the case in the context of the RCU callback that is freeing up * the data, or after a synchronize_rcu() returns. This can be useful * when tearing down multi-linked structures after a grace period * has elapsed. */ #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) /** * rcu_dereference_check() - rcu_dereference with debug checking * @p: The pointer to read, prior to dereferencing * @c: The conditions under which the dereference will take place * * Do an rcu_dereference(), but check that the conditions under which the * dereference will take place are correct. Typically the conditions * indicate the various locking conditions that should be held at that * point. The check should return true if the conditions are satisfied. * An implicit check for being in an RCU read-side critical section * (rcu_read_lock()) is included. * * For example: * * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); * * could be used to indicate to lockdep that foo->bar may only be dereferenced * if either rcu_read_lock() is held, or that the lock required to replace * the bar struct at foo->bar is held. * * Note that the list of conditions may also include indications of when a lock * need not be held, for example during initialisation or destruction of the * target struct: * * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || * atomic_read(&foo->usage) == 0); * * Inserts memory barriers on architectures that require them * (currently only the Alpha), prevents the compiler from refetching * (and from merging fetches), and, more importantly, documents exactly * which pointers are protected by RCU and checks that the pointer is * annotated as __rcu. */ #define rcu_dereference_check(p, c) \ __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu) /** * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking * @p: The pointer to read, prior to dereferencing * @c: The conditions under which the dereference will take place * * This is the RCU-bh counterpart to rcu_dereference_check(). */ #define rcu_dereference_bh_check(p, c) \ __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu) /** * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking * @p: The pointer to read, prior to dereferencing * @c: The conditions under which the dereference will take place * * This is the RCU-sched counterpart to rcu_dereference_check(). */ #define rcu_dereference_sched_check(p, c) \ __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \ __rcu) #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ /* * The tracing infrastructure traces RCU (we want that), but unfortunately * some of the RCU checks causes tracing to lock up the system. * * The tracing version of rcu_dereference_raw() must not call * rcu_read_lock_held(). */ #define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu) /** * rcu_access_index() - fetch RCU index with no dereferencing * @p: The index to read * * Return the value of the specified RCU-protected index, but omit the * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful * when the value of this index is accessed, but the index is not * dereferenced, for example, when testing an RCU-protected index against * -1. Although rcu_access_index() may also be used in cases where * update-side locks prevent the value of the index from changing, you * should instead use rcu_dereference_index_protected() for this use case. */ #define rcu_access_index(p) __rcu_access_index((p), __rcu) /** * rcu_dereference_index_check() - rcu_dereference for indices with debug checking * @p: The pointer to read, prior to dereferencing * @c: The conditions under which the dereference will take place * * Similar to rcu_dereference_check(), but omits the sparse checking. * This allows rcu_dereference_index_check() to be used on integers, * which can then be used as array indices. Attempting to use * rcu_dereference_check() on an integer will give compiler warnings * because the sparse address-space mechanism relies on dereferencing * the RCU-protected pointer. Dereferencing integers is not something * that even gcc will put up with. * * Note that this function does not implicitly check for RCU read-side * critical sections. If this function gains lots of uses, it might * make sense to provide versions for each flavor of RCU, but it does * not make sense as of early 2010. */ #define rcu_dereference_index_check(p, c) \ __rcu_dereference_index_check((p), (c)) /** * rcu_dereference_protected() - fetch RCU pointer when updates prevented * @p: The pointer to read, prior to dereferencing * @c: The conditions under which the dereference will take place * * Return the value of the specified RCU-protected pointer, but omit * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This * is useful in cases where update-side locks prevent the value of the * pointer from changing. Please note that this primitive does -not- * prevent the compiler from repeating this reference or combining it * with other references, so it should not be used without protection * of appropriate locks. * * This function is only for update-side use. Using this function * when protected only by rcu_read_lock() will result in infrequent * but very ugly failures. */ #define rcu_dereference_protected(p, c) \ __rcu_dereference_protected((p), (c), __rcu) /** * rcu_dereference() - fetch RCU-protected pointer for dereferencing * @p: The pointer to read, prior to dereferencing * * This is a simple wrapper around rcu_dereference_check(). */ #define rcu_dereference(p) rcu_dereference_check(p, 0) /** * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing * @p: The pointer to read, prior to dereferencing * * Makes rcu_dereference_check() do the dirty work. */ #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) /** * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing * @p: The pointer to read, prior to dereferencing * * Makes rcu_dereference_check() do the dirty work. */ #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) /** * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism * @p: The pointer to hand off * * This is simply an identity function, but it documents where a pointer * is handed off from RCU to some other synchronization mechanism, for * example, reference counting or locking. In C11, it would map to * kill_dependency(). It could be used as follows: * * rcu_read_lock(); * p = rcu_dereference(gp); * long_lived = is_long_lived(p); * if (long_lived) { * if (!atomic_inc_not_zero(p->refcnt)) * long_lived = false; * else * p = rcu_pointer_handoff(p); * } * rcu_read_unlock(); */ #define rcu_pointer_handoff(p) (p) /** * 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 new 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. * * You can avoid reading and understanding the next paragraph by * following this rule: don't put anything in an rcu_read_lock() RCU * read-side critical section that would block in a !PREEMPT kernel. * But if you want the full story, read on! * * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it * is illegal to block while in an RCU read-side critical section. In * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may * be preempted, but explicit blocking is illegal. Finally, in preemptible * RCU implementations in real-time (with -rt patchset) kernel builds, * RCU read-side critical sections may be preempted and they may also * block, but only when acquiring spinlocks that are subject to priority * inheritance. */ static inline void rcu_read_lock(void) { __rcu_read_lock(); __acquire(RCU); rcu_lock_acquire(&rcu_lock_map); rcu_lockdep_assert(rcu_is_watching(), "rcu_read_lock() used illegally while idle"); } /* * 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_unlock() - marks the end of an RCU read-side critical section. * * See rcu_read_lock() for more information. */ static inline void rcu_read_unlock(void) { rcu_lockdep_assert(rcu_is_watching(), "rcu_read_unlock() used illegally while idle"); rcu_lock_release(&rcu_lock_map); __release(RCU); __rcu_read_unlock(); } /** * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section * * This is equivalent of rcu_read_lock(), but to be used when updates * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since * both call_rcu_bh() and synchronize_rcu_bh() 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(), * though this should at least be commented to avoid confusing people * reading the code. * * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() * must occur in the same context, for example, it is illegal to invoke * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() * was invoked from some other task. */ static inline void rcu_read_lock_bh(void) { local_bh_disable(); __acquire(RCU_BH); rcu_lock_acquire(&rcu_bh_lock_map); rcu_lockdep_assert(rcu_is_watching(), "rcu_read_lock_bh() used illegally while idle"); } /* * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section * * See rcu_read_lock_bh() for more information. */ static inline void rcu_read_unlock_bh(void) { rcu_lockdep_assert(rcu_is_watching(), "rcu_read_unlock_bh() used illegally while idle"); rcu_lock_release(&rcu_bh_lock_map); __release(RCU_BH); local_bh_enable(); } /** * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section * * This is equivalent of rcu_read_lock(), but to be used when updates * are being done using call_rcu_sched() or synchronize_rcu_sched(). * Read-side critical sections can also be introduced by anything that * disables preemption, including local_irq_disable() and friends. * * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() * must occur in the same context, for example, it is illegal to invoke * rcu_read_unlock_sched() from process context if the matching * rcu_read_lock_sched() was invoked from an NMI handler. */ static inline void rcu_read_lock_sched(void) { preempt_disable(); __acquire(RCU_SCHED); rcu_lock_acquire(&rcu_sched_lock_map); rcu_lockdep_assert(rcu_is_watching(), "rcu_read_lock_sched() used illegally while idle"); } /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ static inline notrace void rcu_read_lock_sched_notrace(void) { preempt_disable_notrace(); __acquire(RCU_SCHED); } /* * rcu_read_unlock_sched - marks the end of a RCU-classic critical section * * See rcu_read_lock_sched for more information. */ static inline void rcu_read_unlock_sched(void) { rcu_lockdep_assert(rcu_is_watching(), "rcu_read_unlock_sched() used illegally while idle"); rcu_lock_release(&rcu_sched_lock_map); __release(RCU_SCHED); preempt_enable(); } /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ static inline notrace void rcu_read_unlock_sched_notrace(void) { __release(RCU_SCHED); preempt_enable_notrace(); } /** * rcu_assign_pointer() - assign to RCU-protected pointer * @p: pointer to assign to * @v: value to assign (publish) * * Assigns the specified value to the specified RCU-protected * pointer, ensuring that any concurrent RCU readers will see * any prior initialization. * * Inserts memory barriers on architectures that require them * (which is most of them), 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. * * In some special cases, you may use RCU_INIT_POINTER() instead * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due * to the fact that it does not constrain either the CPU or the compiler. * That said, using RCU_INIT_POINTER() when you should have used * rcu_assign_pointer() is a very bad thing that results in * impossible-to-diagnose memory corruption. So please be careful. * See the RCU_INIT_POINTER() comment header for details. */ #define rcu_assign_pointer(p, v) \ __rcu_assign_pointer((p), (v), __rcu) /** * RCU_INIT_POINTER() - initialize an RCU protected pointer * * Initialize an RCU-protected pointer in special cases where readers * do not need ordering constraints on the CPU or the compiler. These * special cases are: * * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or- * 2. The caller has taken whatever steps are required to prevent * RCU readers from concurrently accessing this pointer -or- * 3. The referenced data structure has already been exposed to * readers either at compile time or via rcu_assign_pointer() -and- * a. You have not made -any- reader-visible changes to * this structure since then -or- * b. It is OK for readers accessing this structure from its * new location to see the old state of the structure. (For * example, the changes were to statistical counters or to * other state where exact synchronization is not required.) * * Failure to follow these rules governing use of RCU_INIT_POINTER() will * result in impossible-to-diagnose memory corruption. As in the structures * will look OK in crash dumps, but any concurrent RCU readers might * see pre-initialized values of the referenced data structure. So * please be very careful how you use RCU_INIT_POINTER()!!! * * If you are creating an RCU-protected linked structure that is accessed * by a single external-to-structure RCU-protected pointer, then you may * use RCU_INIT_POINTER() to initialize the internal RCU-protected * pointers, but you must use rcu_assign_pointer() to initialize the * external-to-structure pointer -after- you have completely initialized * the reader-accessible portions of the linked structure. */ #define RCU_INIT_POINTER(p, v) \ do { \ p = (typeof(*v) __force __rcu *)(v); \ } while (0) /** * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer * * GCC-style initialization for an RCU-protected pointer in a structure field. */ #define RCU_POINTER_INITIALIZER(p, v) \ .p = (typeof(*v) __force __rcu *)(v) /* * Does the specified offset indicate that the corresponding rcu_head * structure can be handled by kfree_rcu()? */ #define __is_kfree_rcu_offset(offset) ((offset) < 4096) /* * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain. */ #define __kfree_rcu(head, offset) \ do { \ BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \ } while (0) /** * kfree_rcu() - kfree an object after a grace period. * @ptr: pointer to kfree * @rcu_head: the name of the struct rcu_head within the type of @ptr. * * Many rcu callbacks functions just call kfree() on the base structure. * These functions are trivial, but their size adds up, and furthermore * when they are used in a kernel module, that module must invoke the * high-latency rcu_barrier() function at module-unload time. * * The kfree_rcu() function handles this issue. Rather than encoding a * function address in the embedded rcu_head structure, kfree_rcu() instead * encodes the offset of the rcu_head structure within the base structure. * Because the functions are not allowed in the low-order 4096 bytes of * kernel virtual memory, offsets up to 4095 bytes can be accommodated. * If the offset is larger than 4095 bytes, a compile-time error will * be generated in __kfree_rcu(). If this error is triggered, you can * either fall back to use of call_rcu() or rearrange the structure to * position the rcu_head structure into the first 4096 bytes. * * Note that the allowable offset might decrease in the future, for example, * to allow something like kmem_cache_free_rcu(). * * The BUILD_BUG_ON check must not involve any function calls, hence the * checks are done in macros here. */ #define kfree_rcu(ptr, rcu_head) \ __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) #ifdef CONFIG_RCU_NOCB_CPU extern bool rcu_is_nocb_cpu(int cpu); #else static inline bool rcu_is_nocb_cpu(int cpu) { return false; } #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ #endif /* __LINUX_RCUPDATE_H */