diff options
Diffstat (limited to 'include/linux/rcupdate.h')
| -rw-r--r-- | include/linux/rcupdate.h | 1080 |
1 files changed, 1080 insertions, 0 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h new file mode 100644 index 000000000..46bd9a331 --- /dev/null +++ b/include/linux/rcupdate.h @@ -0,0 +1,1080 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * Read-Copy Update mechanism for mutual exclusion + * + * Copyright IBM Corporation, 2001 + * + * Author: Dipankar Sarma <dipankar@in.ibm.com> + * + * Based on the original work by Paul McKenney <paulmck@vnet.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> +#include <linux/context_tracking_irq.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))) +#define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b))) +#define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b))) + +/* Exported common interfaces */ +void call_rcu(struct rcu_head *head, rcu_callback_t func); +void rcu_barrier_tasks(void); +void rcu_barrier_tasks_rude(void); +void synchronize_rcu(void); + +struct rcu_gp_oldstate; +unsigned long get_completed_synchronize_rcu(void); +void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp); + +// Maximum number of unsigned long values corresponding to +// not-yet-completed RCU grace periods. +#define NUM_ACTIVE_RCU_POLL_OLDSTATE 2 + +/** + * same_state_synchronize_rcu - Are two old-state values identical? + * @oldstate1: First old-state value. + * @oldstate2: Second old-state value. + * + * The two old-state values must have been obtained from either + * get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or + * get_completed_synchronize_rcu(). Returns @true if the two values are + * identical and @false otherwise. This allows structures whose lifetimes + * are tracked by old-state values to push these values to a list header, + * allowing those structures to be slightly smaller. + */ +static inline bool same_state_synchronize_rcu(unsigned long oldstate1, unsigned long oldstate2) +{ + return oldstate1 == oldstate2; +} + +#ifdef CONFIG_PREEMPT_RCU + +void __rcu_read_lock(void); +void __rcu_read_unlock(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() READ_ONCE(current->rcu_read_lock_nesting) + +#else /* #ifdef CONFIG_PREEMPT_RCU */ + +#ifdef CONFIG_TINY_RCU +#define rcu_read_unlock_strict() do { } while (0) +#else +void rcu_read_unlock_strict(void); +#endif + +static inline void __rcu_read_lock(void) +{ + preempt_disable(); +} + +static inline void __rcu_read_unlock(void) +{ + preempt_enable(); + if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) + rcu_read_unlock_strict(); +} + +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; +void rcu_sched_clock_irq(int user); +void rcu_report_dead(unsigned int cpu); +void rcutree_migrate_callbacks(int cpu); + +#ifdef CONFIG_TASKS_RCU_GENERIC +void rcu_init_tasks_generic(void); +#else +static inline void rcu_init_tasks_generic(void) { } +#endif + +#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 */ + +#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) +void rcu_irq_work_resched(void); +#else +static inline void rcu_irq_work_resched(void) { } +#endif + +#ifdef CONFIG_RCU_NOCB_CPU +void rcu_init_nohz(void); +int rcu_nocb_cpu_offload(int cpu); +int rcu_nocb_cpu_deoffload(int cpu); +void rcu_nocb_flush_deferred_wakeup(void); +#else /* #ifdef CONFIG_RCU_NOCB_CPU */ +static inline void rcu_init_nohz(void) { } +static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; } +static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; } +static inline void rcu_nocb_flush_deferred_wakeup(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 read-side critical sections are forbidden in the inner idle loop, + * that is, between the ct_idle_enter() and the ct_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 { \ + ct_irq_enter_irqson(); \ + do { a; } while (0); \ + ct_irq_exit_irqson(); \ + } while (0) + +/* + * Note a quasi-voluntary context switch for RCU-tasks's benefit. + * This is a macro rather than an inline function to avoid #include hell. + */ +#ifdef CONFIG_TASKS_RCU_GENERIC + +# ifdef CONFIG_TASKS_RCU +# define rcu_tasks_classic_qs(t, preempt) \ + do { \ + if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \ + WRITE_ONCE((t)->rcu_tasks_holdout, false); \ + } while (0) +void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); +void synchronize_rcu_tasks(void); +# else +# define rcu_tasks_classic_qs(t, preempt) do { } while (0) +# define call_rcu_tasks call_rcu +# define synchronize_rcu_tasks synchronize_rcu +# endif + +# ifdef CONFIG_TASKS_TRACE_RCU +// Bits for ->trc_reader_special.b.need_qs field. +#define TRC_NEED_QS 0x1 // Task needs a quiescent state. +#define TRC_NEED_QS_CHECKED 0x2 // Task has been checked for needing quiescent state. + +u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new); +void rcu_tasks_trace_qs_blkd(struct task_struct *t); + +# define rcu_tasks_trace_qs(t) \ + do { \ + int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting); \ + \ + if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) && \ + likely(!___rttq_nesting)) { \ + rcu_trc_cmpxchg_need_qs((t), 0, TRC_NEED_QS_CHECKED); \ + } else if (___rttq_nesting && ___rttq_nesting != INT_MIN && \ + !READ_ONCE((t)->trc_reader_special.b.blocked)) { \ + rcu_tasks_trace_qs_blkd(t); \ + } \ + } while (0) +# else +# define rcu_tasks_trace_qs(t) do { } while (0) +# endif + +#define rcu_tasks_qs(t, preempt) \ +do { \ + rcu_tasks_classic_qs((t), (preempt)); \ + rcu_tasks_trace_qs(t); \ +} while (0) + +# ifdef CONFIG_TASKS_RUDE_RCU +void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func); +void synchronize_rcu_tasks_rude(void); +# endif + +#define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false) +void exit_tasks_rcu_start(void); +void exit_tasks_rcu_stop(void); +void exit_tasks_rcu_finish(void); +#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ +#define rcu_tasks_classic_qs(t, preempt) do { } while (0) +#define rcu_tasks_qs(t, preempt) do { } while (0) +#define rcu_note_voluntary_context_switch(t) do { } while (0) +#define call_rcu_tasks call_rcu +#define synchronize_rcu_tasks synchronize_rcu +static inline void exit_tasks_rcu_start(void) { } +static inline void exit_tasks_rcu_stop(void) { } +static inline void exit_tasks_rcu_finish(void) { } +#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ + +/** + * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period? + * + * As an accident of implementation, an RCU Tasks Trace grace period also + * acts as an RCU grace period. However, this could change at any time. + * Code relying on this accident must call this function to verify that + * this accident is still happening. + * + * You have been warned! + */ +static inline bool rcu_trace_implies_rcu_gp(void) { return true; } + +/** + * cond_resched_tasks_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 PREEMPTION kernels. + */ +#define cond_resched_tasks_rcu_qs() \ +do { \ + rcu_tasks_qs(current, false); \ + cond_resched(); \ +} while (0) + +/* + * Infrastructure to implement the synchronize_() primitives in + * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. + */ + +#if defined(CONFIG_TREE_RCU) +#include <linux/rcutree.h> +#elif defined(CONFIG_TINY_RCU) +#include <linux/rcutiny.h> +#else +#error "Unknown RCU implementation specified to kernel configuration" +#endif + +/* + * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls + * are needed for dynamic initialization and destruction of rcu_head + * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for + * dynamic initialization and destruction of statically allocated rcu_head + * structures. However, rcu_head structures allocated dynamically in the + * heap 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) */ + +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; + +#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, _THIS_IP_); +} + +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); +int rcu_read_lock_any_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(); +} + +static inline int rcu_read_lock_any_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 + * + * This checks debug_lockdep_rcu_enabled() before checking (c) to + * prevent early boot splats due to lockdep not yet being initialized, + * and rechecks it after checking (c) to prevent false-positive splats + * due to races with lockdep being disabled. See commit 3066820034b5dd + * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail. + */ +#define RCU_LOCKDEP_WARN(c, s) \ + do { \ + static bool __section(".data.unlikely") __warned; \ + if (debug_lockdep_rcu_enabled() && (c) && \ + debug_lockdep_rcu_enabled() && !__warned) { \ + __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(); \ + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \ + 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 && (c)) +#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 pointers markings to match different RCU implementations + * (e.g., __srcu), should this make sense in the future. + */ + +#ifdef __CHECKER__ +#define rcu_check_sparse(p, space) \ + ((void)(((typeof(*p) space *)p) == p)) +#else /* #ifdef __CHECKER__ */ +#define rcu_check_sparse(p, space) +#endif /* #else #ifdef __CHECKER__ */ + +#define __unrcu_pointer(p, local) \ +({ \ + typeof(*p) *local = (typeof(*p) *__force)(p); \ + rcu_check_sparse(p, __rcu); \ + ((typeof(*p) __force __kernel *)(local)); \ +}) +/** + * unrcu_pointer - mark a pointer as not being RCU protected + * @p: pointer needing to lose its __rcu property + * + * Converts @p from an __rcu pointer to a __kernel pointer. + * This allows an __rcu pointer to be used with xchg() and friends. + */ +#define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu)) + +#define __rcu_access_pointer(p, local, space) \ +({ \ + typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ + rcu_check_sparse(p, space); \ + ((typeof(*p) __force __kernel *)(local)); \ +}) +#define __rcu_dereference_check(p, local, c, space) \ +({ \ + /* Dependency order vs. p above. */ \ + typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ + RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ + rcu_check_sparse(p, space); \ + ((typeof(*p) __force __kernel *)(local)); \ +}) +#define __rcu_dereference_protected(p, local, c, space) \ +({ \ + RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ + rcu_check_sparse(p, space); \ + ((typeof(*p) __force __kernel *)(p)); \ +}) +#define __rcu_dereference_raw(p, local) \ +({ \ + /* Dependency order vs. p above. */ \ + typeof(p) local = READ_ONCE(p); \ + ((typeof(*p) __force __kernel *)(local)); \ +}) +#define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu)) + +/** + * 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) \ +do { \ + uintptr_t _r_a_p__v = (uintptr_t)(v); \ + rcu_check_sparse(p, __rcu); \ + \ + 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)); \ +} while (0) + +/** + * rcu_replace_pointer() - replace an RCU pointer, returning its old value + * @rcu_ptr: RCU pointer, whose old value is returned + * @ptr: regular pointer + * @c: the lockdep conditions under which the dereference will take place + * + * Perform a replacement, where @rcu_ptr is an RCU-annotated + * pointer and @c is the lockdep argument that is passed to the + * rcu_dereference_protected() call used to read that pointer. The old + * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr. + */ +#define rcu_replace_pointer(rcu_ptr, ptr, c) \ +({ \ + typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ + rcu_assign_pointer((rcu_ptr), (ptr)); \ + __tmp; \ +}) + +/** + * 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 + * lockdep checks for being in an RCU read-side critical section. 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. + * Within an RCU read-side critical section, there is little reason to + * use rcu_access_pointer(). + * + * It is usually best to test the rcu_access_pointer() return value + * directly in order to avoid accidental dereferences being introduced + * by later inattentive changes. In other words, assigning the + * rcu_access_pointer() return value to a local variable results in an + * accident waiting to happen. + * + * 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. However, + * rcu_dereference_protected() is normally preferred for this use case. + */ +#define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __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), __UNIQUE_ID(rcu), \ + (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(). However, + * please note that starting in v5.0 kernels, vanilla RCU grace periods + * wait for local_bh_disable() regions of code in addition to regions of + * code demarked by rcu_read_lock() and rcu_read_unlock(). This means + * that synchronize_rcu(), call_rcu, and friends all take not only + * rcu_read_lock() but also rcu_read_lock_bh() into account. + */ +#define rcu_dereference_bh_check(p, c) \ + __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ + (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(). + * However, please note that starting in v5.0 kernels, vanilla RCU grace + * periods wait for preempt_disable() regions of code in addition to + * regions of code demarked by rcu_read_lock() and rcu_read_unlock(). + * This means that synchronize_rcu(), call_rcu, and friends all take not + * only rcu_read_lock() but also rcu_read_lock_sched() into account. + */ +#define rcu_dereference_sched_check(p, c) \ + __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ + (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_check(p) \ + __rcu_dereference_check((p), __UNIQUE_ID(rcu), 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 + * 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), __UNIQUE_ID(rcu), (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. + * + * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also + * wait for regions of code with preemption disabled, including regions of + * code with interrupts or softirqs disabled. In pre-v5.0 kernels, which + * define synchronize_sched(), only code enclosed within rcu_read_lock() + * and rcu_read_unlock() are guaranteed to be waited for. + * + * 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 !PREEMPTION kernel. + * But if you want the full story, read on! + * + * In non-preemptible RCU implementations (pure 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_PREEMPTION + * 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 __always_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 almost all situations, rcu_read_unlock() is immune from deadlock. + * In recent kernels that have consolidated synchronize_sched() and + * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity + * also extends to the scheduler's runqueue and priority-inheritance + * spinlocks, courtesy of the quiescent-state deferral that is carried + * out when rcu_read_unlock() is invoked with interrupts disabled. + * + * 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 to rcu_read_lock(), but also disables softirqs. + * Note that anything else that disables softirqs can also serve as an RCU + * read-side critical section. However, please note that this equivalence + * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and + * rcu_read_lock_bh() were unrelated. + * + * 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 to rcu_read_lock(), but also disables preemption. + * Read-side critical sections can also be introduced by anything else that + * disables preemption, including local_irq_disable() and friends. However, + * please note that the equivalence to rcu_read_lock() applies only to + * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched() + * were unrelated. + * + * 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_check_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 kvfree_rcu()? + */ +#define __is_kvfree_rcu_offset(offset) ((offset) < 4096) + +/** + * kfree_rcu() - kfree an object after a grace period. + * @ptr: pointer to kfree for both single- and double-argument invocations. + * @rhf: the name of the struct rcu_head within the type of @ptr, + * but only for double-argument invocations. + * + * 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 kvfree_rcu_arg_2(). 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, rhf...) kvfree_rcu(ptr, ## rhf) + +/** + * kvfree_rcu() - kvfree an object after a grace period. + * + * This macro consists of one or two arguments and it is + * based on whether an object is head-less or not. If it + * has a head then a semantic stays the same as it used + * to be before: + * + * kvfree_rcu(ptr, rhf); + * + * where @ptr is a pointer to kvfree(), @rhf is the name + * of the rcu_head structure within the type of @ptr. + * + * When it comes to head-less variant, only one argument + * is passed and that is just a pointer which has to be + * freed after a grace period. Therefore the semantic is + * + * kvfree_rcu(ptr); + * + * where @ptr is the pointer to be freed by kvfree(). + * + * Please note, head-less way of freeing is permitted to + * use from a context that has to follow might_sleep() + * annotation. Otherwise, please switch and embed the + * rcu_head structure within the type of @ptr. + */ +#define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__, \ + kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__) + +#define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME +#define kvfree_rcu_arg_2(ptr, rhf) \ +do { \ + typeof (ptr) ___p = (ptr); \ + \ + if (___p) { \ + BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf))); \ + kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long) \ + (offsetof(typeof(*(ptr)), rhf))); \ + } \ +} while (0) + +#define kvfree_rcu_arg_1(ptr) \ +do { \ + typeof(ptr) ___p = (ptr); \ + \ + if (___p) \ + kvfree_call_rcu(NULL, (rcu_callback_t) (___p)); \ +} while (0) + +/* + * 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 */ + + +/* Has the specified rcu_head structure been handed to call_rcu()? */ + +/** + * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu() + * @rhp: The rcu_head structure to initialize. + * + * If you intend to invoke rcu_head_after_call_rcu() to test whether a + * given rcu_head structure has already been passed to call_rcu(), then + * you must also invoke this rcu_head_init() function on it just after + * allocating that structure. Calls to this function must not race with + * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation. + */ +static inline void rcu_head_init(struct rcu_head *rhp) +{ + rhp->func = (rcu_callback_t)~0L; +} + +/** + * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()? + * @rhp: The rcu_head structure to test. + * @f: The function passed to call_rcu() along with @rhp. + * + * Returns @true if the @rhp has been passed to call_rcu() with @func, + * and @false otherwise. Emits a warning in any other case, including + * the case where @rhp has already been invoked after a grace period. + * Calls to this function must not race with callback invocation. One way + * to avoid such races is to enclose the call to rcu_head_after_call_rcu() + * in an RCU read-side critical section that includes a read-side fetch + * of the pointer to the structure containing @rhp. + */ +static inline bool +rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) +{ + rcu_callback_t func = READ_ONCE(rhp->func); + + if (func == f) + return true; + WARN_ON_ONCE(func != (rcu_callback_t)~0L); + return false; +} + +/* kernel/ksysfs.c definitions */ +extern int rcu_expedited; +extern int rcu_normal; + +#endif /* __LINUX_RCUPDATE_H */ |