| /* |
| * 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/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); |
| #else |
| static inline void rcutorture_record_test_transition(void) |
| { |
| } |
| static inline void rcutorture_record_progress(unsigned long vernum) |
| { |
| } |
| #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)) |
| |
| /* 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. |
| */ |
| 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. |
| */ |
| 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. |
| */ |
| extern void call_rcu_sched(struct rcu_head *head, |
| void (*func)(struct rcu_head *rcu)); |
| |
| extern void synchronize_sched(void); |
| |
| static inline void __rcu_read_lock_bh(void) |
| { |
| local_bh_disable(); |
| } |
| |
| static inline void __rcu_read_unlock_bh(void) |
| { |
| local_bh_enable(); |
| } |
| |
| #ifdef CONFIG_PREEMPT_RCU |
| |
| extern void __rcu_read_lock(void); |
| extern void __rcu_read_unlock(void); |
| 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; |
| |
| #ifdef CONFIG_NO_HZ |
| |
| extern void rcu_enter_nohz(void); |
| extern void rcu_exit_nohz(void); |
| |
| #else /* #ifdef CONFIG_NO_HZ */ |
| |
| static inline void rcu_enter_nohz(void) |
| { |
| } |
| |
| static inline void rcu_exit_nohz(void) |
| { |
| } |
| |
| #endif /* #else #ifdef CONFIG_NO_HZ */ |
| |
| /* |
| * 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 |
| extern void init_rcu_head_on_stack(struct rcu_head *head); |
| extern void destroy_rcu_head_on_stack(struct rcu_head *head); |
| #else /* !CONFIG_DEBUG_OBJECTS_RCU_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 */ |
| |
| #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| |
| extern struct lockdep_map rcu_lock_map; |
| # define rcu_read_acquire() \ |
| lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
| # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) |
| |
| extern struct lockdep_map rcu_bh_lock_map; |
| # define rcu_read_acquire_bh() \ |
| lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
| # define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) |
| |
| extern struct lockdep_map rcu_sched_lock_map; |
| # define rcu_read_acquire_sched() \ |
| lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
| # define rcu_read_release_sched() \ |
| lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) |
| |
| 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. |
| */ |
| static inline int rcu_read_lock_held(void) |
| { |
| if (!debug_lockdep_rcu_enabled()) |
| return 1; |
| 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. |
| */ |
| #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 (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_read_acquire() do { } while (0) |
| # define rcu_read_release() do { } while (0) |
| # define rcu_read_acquire_bh() do { } while (0) |
| # define rcu_read_release_bh() do { } while (0) |
| # define rcu_read_acquire_sched() do { } while (0) |
| # define rcu_read_release_sched() 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 |
| |
| extern int rcu_my_thread_group_empty(void); |
| |
| /** |
| * 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 __warned; \ |
| if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ |
| __warned = true; \ |
| lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ |
| } \ |
| } while (0) |
| |
| #define rcu_sleep_check() \ |
| do { \ |
| 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) \ |
| ({ \ |
| smp_wmb(); \ |
| (p) = (typeof(*v) __force space *)(v); \ |
| }) |
| |
| |
| /** |
| * 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. |
| */ |
| #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), rcu_read_lock_held() || (c), __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), rcu_read_lock_bh_held() || (c), __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), rcu_read_lock_sched_held() || (c), \ |
| __rcu) |
| |
| #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ |
| |
| /** |
| * 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_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 (CONFIG_PREEMPT_RT) 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_read_acquire(); |
| } |
| |
| /* |
| * 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_read_release(); |
| __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. |
| */ |
| static inline void rcu_read_lock_bh(void) |
| { |
| __rcu_read_lock_bh(); |
| __acquire(RCU_BH); |
| rcu_read_acquire_bh(); |
| } |
| |
| /* |
| * 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_read_release_bh(); |
| __release(RCU_BH); |
| __rcu_read_unlock_bh(); |
| } |
| |
| /** |
| * 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. |
| */ |
| static inline void rcu_read_lock_sched(void) |
| { |
| preempt_disable(); |
| __acquire(RCU_SCHED); |
| rcu_read_acquire_sched(); |
| } |
| |
| /* 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_read_release_sched(); |
| __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. 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) \ |
| __rcu_assign_pointer((p), (v), __rcu) |
| |
| /** |
| * RCU_INIT_POINTER() - initialize an RCU protected pointer |
| * |
| * Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep |
| * splats. |
| */ |
| #define RCU_INIT_POINTER(p, v) \ |
| p = (typeof(*v) __force __rcu *)(v) |
| |
| static __always_inline bool __is_kfree_rcu_offset(unsigned long offset) |
| { |
| return offset < 4096; |
| } |
| |
| static __always_inline |
| void __kfree_rcu(struct rcu_head *head, unsigned long offset) |
| { |
| typedef void (*rcu_callback)(struct rcu_head *); |
| |
| BUILD_BUG_ON(!__builtin_constant_p(offset)); |
| |
| /* See the kfree_rcu() header comment. */ |
| BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); |
| |
| call_rcu(head, (rcu_callback)offset); |
| } |
| |
| /** |
| * 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(). |
| */ |
| #define kfree_rcu(ptr, rcu_head) \ |
| __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) |
| |
| #endif /* __LINUX_RCUPDATE_H */ |