1/* SPDX-License-Identifier: GPL-2.0-only */ 2#ifndef _LINUX_RCUREF_H 3#define _LINUX_RCUREF_H 4 5#include <linux/atomic.h> 6#include <linux/bug.h> 7#include <linux/limits.h> 8#include <linux/lockdep.h> 9#include <linux/preempt.h> 10#include <linux/rcupdate.h> 11 12#define RCUREF_ONEREF 0x00000000U 13#define RCUREF_MAXREF 0x7FFFFFFFU 14#define RCUREF_SATURATED 0xA0000000U 15#define RCUREF_RELEASED 0xC0000000U 16#define RCUREF_DEAD 0xE0000000U 17#define RCUREF_NOREF 0xFFFFFFFFU 18 19/** 20 * rcuref_init - Initialize a rcuref reference count with the given reference count 21 * @ref: Pointer to the reference count 22 * @cnt: The initial reference count typically '1' 23 */ 24static inline void rcuref_init(rcuref_t *ref, unsigned int cnt) 25{ 26 atomic_set(&ref->refcnt, cnt - 1); 27} 28 29/** 30 * rcuref_read - Read the number of held reference counts of a rcuref 31 * @ref: Pointer to the reference count 32 * 33 * Return: The number of held references (0 ... N) 34 */ 35static inline unsigned int rcuref_read(rcuref_t *ref) 36{ 37 unsigned int c = atomic_read(&ref->refcnt); 38 39 /* Return 0 if within the DEAD zone. */ 40 return c >= RCUREF_RELEASED ? 0 : c + 1; 41} 42 43extern __must_check bool rcuref_get_slowpath(rcuref_t *ref); 44 45/** 46 * rcuref_get - Acquire one reference on a rcuref reference count 47 * @ref: Pointer to the reference count 48 * 49 * Similar to atomic_inc_not_zero() but saturates at RCUREF_MAXREF. 50 * 51 * Provides no memory ordering, it is assumed the caller has guaranteed the 52 * object memory to be stable (RCU, etc.). It does provide a control dependency 53 * and thereby orders future stores. See documentation in lib/rcuref.c 54 * 55 * Return: 56 * False if the attempt to acquire a reference failed. This happens 57 * when the last reference has been put already 58 * 59 * True if a reference was successfully acquired 60 */ 61static inline __must_check bool rcuref_get(rcuref_t *ref) 62{ 63 /* 64 * Unconditionally increase the reference count. The saturation and 65 * dead zones provide enough tolerance for this. 66 */ 67 if (likely(!atomic_add_negative_relaxed(1, &ref->refcnt))) 68 return true; 69 70 /* Handle the cases inside the saturation and dead zones */ 71 return rcuref_get_slowpath(ref); 72} 73 74extern __must_check bool rcuref_put_slowpath(rcuref_t *ref); 75 76/* 77 * Internal helper. Do not invoke directly. 78 */ 79static __always_inline __must_check bool __rcuref_put(rcuref_t *ref) 80{ 81 RCU_LOCKDEP_WARN(!rcu_read_lock_held() && preemptible(), 82 "suspicious rcuref_put_rcusafe() usage"); 83 /* 84 * Unconditionally decrease the reference count. The saturation and 85 * dead zones provide enough tolerance for this. 86 */ 87 if (likely(!atomic_add_negative_release(-1, &ref->refcnt))) 88 return false; 89 90 /* 91 * Handle the last reference drop and cases inside the saturation 92 * and dead zones. 93 */ 94 return rcuref_put_slowpath(ref); 95} 96 97/** 98 * rcuref_put_rcusafe -- Release one reference for a rcuref reference count RCU safe 99 * @ref: Pointer to the reference count 100 * 101 * Provides release memory ordering, such that prior loads and stores are done 102 * before, and provides an acquire ordering on success such that free() 103 * must come after. 104 * 105 * Can be invoked from contexts, which guarantee that no grace period can 106 * happen which would free the object concurrently if the decrement drops 107 * the last reference and the slowpath races against a concurrent get() and 108 * put() pair. rcu_read_lock()'ed and atomic contexts qualify. 109 * 110 * Return: 111 * True if this was the last reference with no future references 112 * possible. This signals the caller that it can safely release the 113 * object which is protected by the reference counter. 114 * 115 * False if there are still active references or the put() raced 116 * with a concurrent get()/put() pair. Caller is not allowed to 117 * release the protected object. 118 */ 119static inline __must_check bool rcuref_put_rcusafe(rcuref_t *ref) 120{ 121 return __rcuref_put(ref); 122} 123 124/** 125 * rcuref_put -- Release one reference for a rcuref reference count 126 * @ref: Pointer to the reference count 127 * 128 * Can be invoked from any context. 129 * 130 * Provides release memory ordering, such that prior loads and stores are done 131 * before, and provides an acquire ordering on success such that free() 132 * must come after. 133 * 134 * Return: 135 * 136 * True if this was the last reference with no future references 137 * possible. This signals the caller that it can safely schedule the 138 * object, which is protected by the reference counter, for 139 * deconstruction. 140 * 141 * False if there are still active references or the put() raced 142 * with a concurrent get()/put() pair. Caller is not allowed to 143 * deconstruct the protected object. 144 */ 145static inline __must_check bool rcuref_put(rcuref_t *ref) 146{ 147 bool released; 148 149 preempt_disable(); 150 released = __rcuref_put(ref); 151 preempt_enable(); 152 return released; 153} 154 155#endif 156