| /* |
| * 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, you can access it online at |
| * http://www.gnu.org/licenses/gpl-2.0.html. |
| * |
| * 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/compiler.h> |
| #include <linux/atomic.h> |
| #include <linux/irqflags.h> |
| #include <linux/preempt.h> |
| #include <linux/bottom_half.h> |
| #include <linux/lockdep.h> |
| #include <asm/processor.h> |
| #include <linux/cpumask.h> |
| |
| #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 |
| void call_rcu(struct rcu_head *head, rcu_callback_t func); |
| #else /* #ifdef CONFIG_PREEMPT_RCU */ |
| #define call_rcu call_rcu_sched |
| #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
| |
| void call_rcu_bh(struct rcu_head *head, rcu_callback_t func); |
| void call_rcu_sched(struct rcu_head *head, rcu_callback_t func); |
| void synchronize_sched(void); |
| void rcu_barrier_tasks(void); |
| |
| #ifdef CONFIG_PREEMPT_RCU |
| |
| void __rcu_read_lock(void); |
| void __rcu_read_unlock(void); |
| 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) |
| { |
| if (IS_ENABLED(CONFIG_PREEMPT_COUNT)) |
| preempt_disable(); |
| } |
| |
| static inline void __rcu_read_unlock(void) |
| { |
| if (IS_ENABLED(CONFIG_PREEMPT_COUNT)) |
| 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 */ |
| void rcu_init(void); |
| extern int rcu_scheduler_active __read_mostly; |
| void rcu_sched_qs(void); |
| void rcu_bh_qs(void); |
| void rcu_check_callbacks(int user); |
| void rcu_report_dead(unsigned int cpu); |
| void rcu_cpu_starting(unsigned int cpu); |
| void rcutree_migrate_callbacks(int cpu); |
| |
| #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_NO_HZ_FULL |
| void rcu_user_enter(void); |
| void rcu_user_exit(void); |
| #else |
| static inline void rcu_user_enter(void) { } |
| static inline void rcu_user_exit(void) { } |
| #endif /* CONFIG_NO_HZ_FULL */ |
| |
| #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 attention, invoke its argument |
| * (in this example, calling 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 not indefinitely (but the limit is |
| * on the order of a million or so, even on 32-bit systems). It is |
| * not legal to block within RCU_NONIDLE(), nor is it permissible to |
| * transfer control either into or out of RCU_NONIDLE()'s statement. |
| */ |
| #define RCU_NONIDLE(a) \ |
| do { \ |
| rcu_irq_enter_irqson(); \ |
| do { a; } while (0); \ |
| rcu_irq_exit_irqson(); \ |
| } while (0) |
| |
| /* |
| * Note a voluntary context switch for RCU-tasks benefit. This is a |
| * macro rather than an inline function to avoid #include hell. |
| */ |
| #ifdef CONFIG_TASKS_RCU |
| #define rcu_note_voluntary_context_switch_lite(t) \ |
| do { \ |
| if (READ_ONCE((t)->rcu_tasks_holdout)) \ |
| WRITE_ONCE((t)->rcu_tasks_holdout, false); \ |
| } while (0) |
| #define rcu_note_voluntary_context_switch(t) \ |
| do { \ |
| rcu_all_qs(); \ |
| rcu_note_voluntary_context_switch_lite(t); \ |
| } while (0) |
| void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); |
| void synchronize_rcu_tasks(void); |
| void exit_tasks_rcu_start(void); |
| void exit_tasks_rcu_finish(void); |
| #else /* #ifdef CONFIG_TASKS_RCU */ |
| #define rcu_note_voluntary_context_switch_lite(t) do { } while (0) |
| #define rcu_note_voluntary_context_switch(t) rcu_all_qs() |
| #define call_rcu_tasks call_rcu_sched |
| #define synchronize_rcu_tasks synchronize_sched |
| static inline void exit_tasks_rcu_start(void) { } |
| static inline void exit_tasks_rcu_finish(void) { } |
| #endif /* #else #ifdef CONFIG_TASKS_RCU */ |
| |
| /** |
| * cond_resched_rcu_qs - Report potential quiescent states to RCU |
| * |
| * This macro resembles cond_resched(), except that it is defined to |
| * report potential quiescent states to RCU-tasks even if the cond_resched() |
| * machinery were to be shut off, as some advocate for PREEMPT kernels. |
| */ |
| #define cond_resched_rcu_qs() \ |
| do { \ |
| if (!cond_resched()) \ |
| rcu_note_voluntary_context_switch(current); \ |
| } while (0) |
| |
| /* |
| * Infrastructure to implement the synchronize_() primitives in |
| * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. |
| */ |
| |
| #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) |
| #include <linux/rcutree.h> |
| #elif defined(CONFIG_TINY_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 true; } |
| #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, 0, 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 struct lockdep_map rcu_callback_map; |
| int debug_lockdep_rcu_enabled(void); |
| int rcu_read_lock_held(void); |
| int rcu_read_lock_bh_held(void); |
| int rcu_read_lock_sched_held(void); |
| |
| #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; |
| } |
| |
| static inline int rcu_read_lock_sched_held(void) |
| { |
| return !preemptible(); |
| } |
| #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
| |
| #ifdef CONFIG_PROVE_RCU |
| |
| /** |
| * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met |
| * @c: condition to check |
| * @s: informative message |
| */ |
| #define RCU_LOCKDEP_WARN(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_WARN(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_WARN(lock_is_held(&rcu_bh_lock_map), \ |
| "Illegal context switch in RCU-bh read-side critical section"); \ |
| RCU_LOCKDEP_WARN(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_WARN(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)READ_ONCE(p); \ |
| rcu_dereference_sparse(p, space); \ |
| ((typeof(*p) __force __kernel *)(_________p1)); \ |
| }) |
| #define __rcu_dereference_check(p, c, space) \ |
| ({ \ |
| /* Dependency order vs. p above. */ \ |
| typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \ |
| RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ |
| rcu_dereference_sparse(p, space); \ |
| ((typeof(*p) __force __kernel *)(________p1)); \ |
| }) |
| #define __rcu_dereference_protected(p, c, space) \ |
| ({ \ |
| RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ |
| rcu_dereference_sparse(p, space); \ |
| ((typeof(*p) __force __kernel *)(p)); \ |
| }) |
| #define rcu_dereference_raw(p) \ |
| ({ \ |
| /* Dependency order vs. p above. */ \ |
| typeof(p) ________p1 = lockless_dereference(p); \ |
| ((typeof(*p) __force __kernel *)(________p1)); \ |
| }) |
| |
| /** |
| * RCU_INITIALIZER() - statically initialize an RCU-protected global variable |
| * @v: The value to statically initialize with. |
| */ |
| #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) |
| |
| /** |
| * 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. |
| * |
| * Note that rcu_assign_pointer() evaluates each of its arguments only |
| * once, appearances notwithstanding. One of the "extra" evaluations |
| * is in typeof() and the other visible only to sparse (__CHECKER__), |
| * neither of which actually execute the argument. As with most cpp |
| * macros, this execute-arguments-only-once property is important, so |
| * please be careful when making changes to rcu_assign_pointer() and the |
| * other macros that it invokes. |
| */ |
| #define rcu_assign_pointer(p, v) \ |
| ({ \ |
| uintptr_t _r_a_p__v = (uintptr_t)(v); \ |
| \ |
| if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \ |
| WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ |
| else \ |
| smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ |
| _r_a_p__v; \ |
| }) |
| |
| /** |
| * rcu_swap_protected() - swap an RCU and a regular pointer |
| * @rcu_ptr: RCU pointer |
| * @ptr: regular pointer |
| * @c: the conditions under which the dereference will take place |
| * |
| * Perform swap(@rcu_ptr, @ptr) where @rcu_ptr is an RCU-annotated pointer and |
| * @c is the argument that is passed to the rcu_dereference_protected() call |
| * used to read that pointer. |
| */ |
| #define rcu_swap_protected(rcu_ptr, ptr, c) do { \ |
| typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ |
| rcu_assign_pointer((rcu_ptr), (ptr)); \ |
| (ptr) = __tmp; \ |
| } 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 READ_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) |
| |
| /* |
| * The tracing infrastructure traces RCU (we want that), but unfortunately |
| * some of the RCU checks causes tracing to lock up the system. |
| * |
| * The no-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_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 READ_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 (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_WARN(!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. |
| * |
| * In most situations, rcu_read_unlock() is immune from deadlock. |
| * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock() |
| * is responsible for deboosting, which it does via rt_mutex_unlock(). |
| * Unfortunately, this function acquires the scheduler's runqueue and |
| * priority-inheritance spinlocks. This means that deadlock could result |
| * if the caller of rcu_read_unlock() already holds one of these locks or |
| * any lock that is ever acquired while holding them; or any lock which |
| * can be taken from interrupt context because rcu_boost()->rt_mutex_lock() |
| * does not disable irqs while taking ->wait_lock. |
| * |
| * That said, RCU readers are never priority boosted unless they were |
| * preempted. Therefore, one way to avoid deadlock is to make sure |
| * that preemption never happens within any RCU read-side critical |
| * section whose outermost rcu_read_unlock() is called with one of |
| * rt_mutex_unlock()'s locks held. Such preemption can be avoided in |
| * a number of ways, for example, by invoking preempt_disable() before |
| * critical section's outermost rcu_read_lock(). |
| * |
| * Given that the set of locks acquired by rt_mutex_unlock() might change |
| * at any time, a somewhat more future-proofed approach is to make sure |
| * that that preemption never happens within any RCU read-side critical |
| * section whose outermost rcu_read_unlock() is called with irqs disabled. |
| * This approach relies on the fact that rt_mutex_unlock() currently only |
| * acquires irq-disabled locks. |
| * |
| * The second of these two approaches is best in most situations, |
| * however, the first approach can also be useful, at least to those |
| * developers willing to keep abreast of the set of locks acquired by |
| * rt_mutex_unlock(). |
| * |
| * See rcu_read_lock() for more information. |
| */ |
| static inline void rcu_read_unlock(void) |
| { |
| RCU_LOCKDEP_WARN(!rcu_is_watching(), |
| "rcu_read_unlock() used illegally while idle"); |
| __release(RCU); |
| __rcu_read_unlock(); |
| rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ |
| } |
| |
| /** |
| * 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_WARN(!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_WARN(!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_WARN(!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_WARN(!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_INIT_POINTER() - initialize an RCU protected pointer |
| * @p: The pointer to be initialized. |
| * @v: The value to initialized the pointer to. |
| * |
| * 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. |
| * |
| * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no |
| * ordering guarantees for either the CPU or the compiler. |
| */ |
| #define RCU_INIT_POINTER(p, v) \ |
| do { \ |
| rcu_dereference_sparse(p, __rcu); \ |
| WRITE_ONCE(p, RCU_INITIALIZER(v)); \ |
| } while (0) |
| |
| /** |
| * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer |
| * @p: The pointer to be initialized. |
| * @v: The value to initialized the pointer to. |
| * |
| * GCC-style initialization for an RCU-protected pointer in a structure field. |
| */ |
| #define RCU_POINTER_INITIALIZER(p, v) \ |
| .p = RCU_INITIALIZER(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, (rcu_callback_t)(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)) |
| |
| |
| /* |
| * Place this after a lock-acquisition primitive to guarantee that |
| * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies |
| * if the UNLOCK and LOCK are executed by the same CPU or if the |
| * UNLOCK and LOCK operate on the same lock variable. |
| */ |
| #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE |
| #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ |
| #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
| #define smp_mb__after_unlock_lock() do { } while (0) |
| #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
| |
| |
| #endif /* __LINUX_RCUPDATE_H */ |