1 /* SPDX-License-Identifier: GPL-2.0+ */ 2 /* 3 * Sleepable Read-Copy Update mechanism for mutual exclusion, 4 * tree variant. 5 * 6 * Copyright (C) IBM Corporation, 2017 7 * 8 * Author: Paul McKenney <[email protected]> 9 */ 10 11 #ifndef _LINUX_SRCU_TREE_H 12 #define _LINUX_SRCU_TREE_H 13 14 #include <linux/rcu_node_tree.h> 15 #include <linux/completion.h> 16 17 struct srcu_node; 18 struct srcu_struct; 19 20 /* One element of the srcu_data srcu_ctrs array. */ 21 struct srcu_ctr { 22 atomic_long_t srcu_locks; /* Locks per CPU. */ 23 atomic_long_t srcu_unlocks; /* Unlocks per CPU. */ 24 }; 25 26 /* 27 * Per-CPU structure feeding into leaf srcu_node, similar in function 28 * to rcu_node. 29 */ 30 struct srcu_data { 31 /* Read-side state. */ 32 struct srcu_ctr srcu_ctrs[2]; /* Locks and unlocks per CPU. */ 33 int srcu_reader_flavor; /* Reader flavor for srcu_struct structure? */ 34 /* Values: SRCU_READ_FLAVOR_.* */ 35 36 /* Update-side state. */ 37 spinlock_t __private lock ____cacheline_internodealigned_in_smp; 38 struct rcu_segcblist srcu_cblist; /* List of callbacks.*/ 39 unsigned long srcu_gp_seq_needed; /* Furthest future GP needed. */ 40 unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ 41 bool srcu_cblist_invoking; /* Invoking these CBs? */ 42 struct timer_list delay_work; /* Delay for CB invoking */ 43 struct work_struct work; /* Context for CB invoking. */ 44 struct rcu_head srcu_barrier_head; /* For srcu_barrier() use. */ 45 struct srcu_node *mynode; /* Leaf srcu_node. */ 46 unsigned long grpmask; /* Mask for leaf srcu_node */ 47 /* ->srcu_data_have_cbs[]. */ 48 int cpu; 49 struct srcu_struct *ssp; 50 }; 51 52 /* 53 * Node in SRCU combining tree, similar in function to rcu_data. 54 */ 55 struct srcu_node { 56 spinlock_t __private lock; 57 unsigned long srcu_have_cbs[4]; /* GP seq for children having CBs, but only */ 58 /* if greater than ->srcu_gp_seq. */ 59 unsigned long srcu_data_have_cbs[4]; /* Which srcu_data structs have CBs for given GP? */ 60 unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ 61 struct srcu_node *srcu_parent; /* Next up in tree. */ 62 int grplo; /* Least CPU for node. */ 63 int grphi; /* Biggest CPU for node. */ 64 }; 65 66 /* 67 * Per-SRCU-domain structure, update-side data linked from srcu_struct. 68 */ 69 struct srcu_usage { 70 struct srcu_node *node; /* Combining tree. */ 71 struct srcu_node *level[RCU_NUM_LVLS + 1]; 72 /* First node at each level. */ 73 int srcu_size_state; /* Small-to-big transition state. */ 74 struct mutex srcu_cb_mutex; /* Serialize CB preparation. */ 75 spinlock_t __private lock; /* Protect counters and size state. */ 76 struct mutex srcu_gp_mutex; /* Serialize GP work. */ 77 unsigned long srcu_gp_seq; /* Grace-period seq #. */ 78 unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */ 79 unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ 80 unsigned long srcu_gp_start; /* Last GP start timestamp (jiffies) */ 81 unsigned long srcu_last_gp_end; /* Last GP end timestamp (ns) */ 82 unsigned long srcu_size_jiffies; /* Current contention-measurement interval. */ 83 unsigned long srcu_n_lock_retries; /* Contention events in current interval. */ 84 unsigned long srcu_n_exp_nodelay; /* # expedited no-delays in current GP phase. */ 85 bool sda_is_static; /* May ->sda be passed to free_percpu()? */ 86 unsigned long srcu_barrier_seq; /* srcu_barrier seq #. */ 87 struct mutex srcu_barrier_mutex; /* Serialize barrier ops. */ 88 struct completion srcu_barrier_completion; 89 /* Awaken barrier rq at end. */ 90 atomic_t srcu_barrier_cpu_cnt; /* # CPUs not yet posting a */ 91 /* callback for the barrier */ 92 /* operation. */ 93 unsigned long reschedule_jiffies; 94 unsigned long reschedule_count; 95 struct delayed_work work; 96 struct srcu_struct *srcu_ssp; 97 }; 98 99 /* 100 * Per-SRCU-domain structure, similar in function to rcu_state. 101 */ 102 struct srcu_struct { 103 unsigned int srcu_idx; /* Current rdr array element. */ 104 struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ 105 struct lockdep_map dep_map; 106 struct srcu_usage *srcu_sup; /* Update-side data. */ 107 }; 108 109 // Values for size state variable (->srcu_size_state). Once the state 110 // has been set to SRCU_SIZE_ALLOC, the grace-period code advances through 111 // this state machine one step per grace period until the SRCU_SIZE_BIG state 112 // is reached. Otherwise, the state machine remains in the SRCU_SIZE_SMALL 113 // state indefinitely. 114 #define SRCU_SIZE_SMALL 0 // No srcu_node combining tree, ->node == NULL 115 #define SRCU_SIZE_ALLOC 1 // An srcu_node tree is being allocated, initialized, 116 // and then referenced by ->node. It will not be used. 117 #define SRCU_SIZE_WAIT_BARRIER 2 // The srcu_node tree starts being used by everything 118 // except call_srcu(), especially by srcu_barrier(). 119 // By the end of this state, all CPUs and threads 120 // are aware of this tree's existence. 121 #define SRCU_SIZE_WAIT_CALL 3 // The srcu_node tree starts being used by call_srcu(). 122 // By the end of this state, all of the call_srcu() 123 // invocations that were running on a non-boot CPU 124 // and using the boot CPU's callback queue will have 125 // completed. 126 #define SRCU_SIZE_WAIT_CBS1 4 // Don't trust the ->srcu_have_cbs[] grace-period 127 #define SRCU_SIZE_WAIT_CBS2 5 // sequence elements or the ->srcu_data_have_cbs[] 128 #define SRCU_SIZE_WAIT_CBS3 6 // CPU-bitmask elements until all four elements of 129 #define SRCU_SIZE_WAIT_CBS4 7 // each array have been initialized. 130 #define SRCU_SIZE_BIG 8 // The srcu_node combining tree is fully initialized 131 // and all aspects of it are being put to use. 132 133 /* Values for state variable (bottom bits of ->srcu_gp_seq). */ 134 #define SRCU_STATE_IDLE 0 135 #define SRCU_STATE_SCAN1 1 136 #define SRCU_STATE_SCAN2 2 137 138 /* 139 * Values for initializing gp sequence fields. Higher values allow wrap arounds to 140 * occur earlier. 141 * The second value with state is useful in the case of static initialization of 142 * srcu_usage where srcu_gp_seq_needed is expected to have some state value in its 143 * lower bits (or else it will appear to be already initialized within 144 * the call check_init_srcu_struct()). 145 */ 146 #define SRCU_GP_SEQ_INITIAL_VAL ((0UL - 100UL) << RCU_SEQ_CTR_SHIFT) 147 #define SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE (SRCU_GP_SEQ_INITIAL_VAL - 1) 148 149 #define __SRCU_USAGE_INIT(name) \ 150 { \ 151 .lock = __SPIN_LOCK_UNLOCKED(name.lock), \ 152 .srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL, \ 153 .srcu_gp_seq_needed = SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE, \ 154 .srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL, \ 155 .work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0), \ 156 } 157 158 #define __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ 159 .srcu_sup = &usage_name, \ 160 __SRCU_DEP_MAP_INIT(name) 161 162 #define __SRCU_STRUCT_INIT_MODULE(name, usage_name) \ 163 { \ 164 __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ 165 } 166 167 #define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name) \ 168 { \ 169 .sda = &pcpu_name, \ 170 __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ 171 } 172 173 /* 174 * Define and initialize a srcu struct at build time. 175 * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it. 176 * 177 * Note that although DEFINE_STATIC_SRCU() hides the name from other 178 * files, the per-CPU variable rules nevertheless require that the 179 * chosen name be globally unique. These rules also prohibit use of 180 * DEFINE_STATIC_SRCU() within a function. If these rules are too 181 * restrictive, declare the srcu_struct manually. For example, in 182 * each file: 183 * 184 * static struct srcu_struct my_srcu; 185 * 186 * Then, before the first use of each my_srcu, manually initialize it: 187 * 188 * init_srcu_struct(&my_srcu); 189 * 190 * See include/linux/percpu-defs.h for the rules on per-CPU variables. 191 */ 192 #ifdef MODULE 193 # define __DEFINE_SRCU(name, is_static) \ 194 static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ 195 is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage); \ 196 extern struct srcu_struct * const __srcu_struct_##name; \ 197 struct srcu_struct * const __srcu_struct_##name \ 198 __section("___srcu_struct_ptrs") = &name 199 #else 200 # define __DEFINE_SRCU(name, is_static) \ 201 static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data); \ 202 static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ 203 is_static struct srcu_struct name = \ 204 __SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data) 205 #endif 206 #define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */) 207 #define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static) 208 209 void synchronize_srcu_expedited(struct srcu_struct *ssp); 210 void srcu_barrier(struct srcu_struct *ssp); 211 void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf); 212 213 /* 214 * Counts the new reader in the appropriate per-CPU element of the 215 * srcu_struct. Returns an index that must be passed to the matching 216 * srcu_read_unlock_lite(). 217 * 218 * Note that this_cpu_inc() is an RCU read-side critical section either 219 * because it disables interrupts, because it is a single instruction, 220 * or because it is a read-modify-write atomic operation, depending on 221 * the whims of the architecture. 222 */ 223 static inline int __srcu_read_lock_lite(struct srcu_struct *ssp) 224 { 225 int idx; 226 227 RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite()."); 228 idx = READ_ONCE(ssp->srcu_idx) & 0x1; 229 this_cpu_inc(ssp->sda->srcu_ctrs[idx].srcu_locks.counter); /* Y */ 230 barrier(); /* Avoid leaking the critical section. */ 231 return idx; 232 } 233 234 /* 235 * Removes the count for the old reader from the appropriate 236 * per-CPU element of the srcu_struct. Note that this may well be a 237 * different CPU than that which was incremented by the corresponding 238 * srcu_read_lock_lite(), but it must be within the same task. 239 * 240 * Note that this_cpu_inc() is an RCU read-side critical section either 241 * because it disables interrupts, because it is a single instruction, 242 * or because it is a read-modify-write atomic operation, depending on 243 * the whims of the architecture. 244 */ 245 static inline void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx) 246 { 247 barrier(); /* Avoid leaking the critical section. */ 248 this_cpu_inc(ssp->sda->srcu_ctrs[idx].srcu_unlocks.counter); /* Z */ 249 RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_lite()."); 250 } 251 252 void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor); 253 254 // Record _lite() usage even for CONFIG_PROVE_RCU=n kernels. 255 static inline void srcu_check_read_flavor_lite(struct srcu_struct *ssp) 256 { 257 struct srcu_data *sdp = raw_cpu_ptr(ssp->sda); 258 259 if (likely(READ_ONCE(sdp->srcu_reader_flavor) & SRCU_READ_FLAVOR_LITE)) 260 return; 261 262 // Note that the cmpxchg() in __srcu_check_read_flavor() is fully ordered. 263 __srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE); 264 } 265 266 // Record non-_lite() usage only for CONFIG_PROVE_RCU=y kernels. 267 static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) 268 { 269 if (IS_ENABLED(CONFIG_PROVE_RCU)) 270 __srcu_check_read_flavor(ssp, read_flavor); 271 } 272 273 #endif 274