| /* 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 <linux/cleanup.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)) |
| |
| /* 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 */ |
| |
| #ifdef CONFIG_RCU_LAZY |
| void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func); |
| #else |
| static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func) |
| { |
| call_rcu(head, func); |
| } |
| #endif |
| |
| /* Internal to kernel */ |
| void rcu_init(void); |
| extern int rcu_scheduler_active; |
| void rcu_sched_clock_irq(int user); |
| |
| #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 */ |
| |
| /* |
| * 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(); |
| } |
| |
| static inline int debug_lockdep_rcu_enabled(void) |
| { |
| return 0; |
| } |
| |
| #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 double-argument invocations. |
| * @rhf: 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 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. |
| * |
| * The object to be freed can be allocated either by kmalloc() or |
| * kmem_cache_alloc(). |
| * |
| * Note that the allowable offset might decrease in the future. |
| * |
| * 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_arg_2(ptr, rhf) |
| #define kvfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf) |
| |
| /** |
| * kfree_rcu_mightsleep() - kfree an object after a grace period. |
| * @ptr: pointer to kfree for single-argument invocations. |
| * |
| * 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 |
| * |
| * kfree_rcu_mightsleep(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 kfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr) |
| #define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr) |
| |
| #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), (void *) (___p)); \ |
| } \ |
| } while (0) |
| |
| #define kvfree_rcu_arg_1(ptr) \ |
| do { \ |
| typeof(ptr) ___p = (ptr); \ |
| \ |
| if (___p) \ |
| kvfree_call_rcu(NULL, (void *) (___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; |
| |
| DEFINE_LOCK_GUARD_0(rcu, rcu_read_lock(), rcu_read_unlock()) |
| |
| #endif /* __LINUX_RCUPDATE_H */ |