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 <paulmck@linux.ibm.com> 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 struct srcu_ctr __percpu *srcu_ctrp; 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_ctrp = &pcpu_name.srcu_ctrs[0], \ 171 __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ 172 } 173 174 /* 175 * Define and initialize a srcu struct at build time. 176 * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it. 177 * 178 * Note that although DEFINE_STATIC_SRCU() hides the name from other 179 * files, the per-CPU variable rules nevertheless require that the 180 * chosen name be globally unique. These rules also prohibit use of 181 * DEFINE_STATIC_SRCU() within a function. If these rules are too 182 * restrictive, declare the srcu_struct manually. For example, in 183 * each file: 184 * 185 * static struct srcu_struct my_srcu; 186 * 187 * Then, before the first use of each my_srcu, manually initialize it: 188 * 189 * init_srcu_struct(&my_srcu); 190 * 191 * See include/linux/percpu-defs.h for the rules on per-CPU variables. 192 */ 193 #ifdef MODULE 194 # define __DEFINE_SRCU(name, is_static) \ 195 static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ 196 is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage); \ 197 extern struct srcu_struct * const __srcu_struct_##name; \ 198 struct srcu_struct * const __srcu_struct_##name \ 199 __section("___srcu_struct_ptrs") = &name 200 #else 201 # define __DEFINE_SRCU(name, is_static) \ 202 static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data); \ 203 static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ 204 is_static struct srcu_struct name = \ 205 __SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data) 206 #endif 207 #define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */) 208 #define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static) 209 210 int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp); 211 void synchronize_srcu_expedited(struct srcu_struct *ssp); 212 void srcu_barrier(struct srcu_struct *ssp); 213 void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf); 214 215 // Converts a per-CPU pointer to an ->srcu_ctrs[] array element to that 216 // element's index. 217 static inline bool __srcu_ptr_to_ctr(struct srcu_struct *ssp, struct srcu_ctr __percpu *scpp) 218 { 219 return scpp - &ssp->sda->srcu_ctrs[0]; 220 } 221 222 // Converts an integer to a per-CPU pointer to the corresponding 223 // ->srcu_ctrs[] array element. 224 static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ssp, int idx) 225 { 226 return &ssp->sda->srcu_ctrs[idx]; 227 } 228 229 /* 230 * Counts the new reader in the appropriate per-CPU element of the 231 * srcu_struct. Returns a pointer that must be passed to the matching 232 * srcu_read_unlock_fast(). 233 * 234 * Note that both this_cpu_inc() and atomic_long_inc() are RCU read-side 235 * critical sections either because they disables interrupts, because 236 * they are a single instruction, or because they are read-modify-write 237 * atomic operations, depending on the whims of the architecture. 238 * This matters because the SRCU-fast grace-period mechanism uses either 239 * synchronize_rcu() or synchronize_rcu_expedited(), that is, RCU, 240 * *not* SRCU, in order to eliminate the need for the read-side smp_mb() 241 * invocations that are used by srcu_read_lock() and srcu_read_unlock(). 242 * The __srcu_read_unlock_fast() function also relies on this same RCU 243 * (again, *not* SRCU) trick to eliminate the need for smp_mb(). 244 * 245 * The key point behind this RCU trick is that if any part of a given 246 * RCU reader precedes the beginning of a given RCU grace period, then 247 * the entirety of that RCU reader and everything preceding it happens 248 * before the end of that same RCU grace period. Similarly, if any part 249 * of a given RCU reader follows the end of a given RCU grace period, 250 * then the entirety of that RCU reader and everything following it 251 * happens after the beginning of that same RCU grace period. Therefore, 252 * the operations labeled Y in __srcu_read_lock_fast() and those labeled Z 253 * in __srcu_read_unlock_fast() are ordered against the corresponding SRCU 254 * read-side critical section from the viewpoint of the SRCU grace period. 255 * This is all the ordering that is required, hence no calls to smp_mb(). 256 * 257 * This means that __srcu_read_lock_fast() is not all that fast 258 * on architectures that support NMIs but do not supply NMI-safe 259 * implementations of this_cpu_inc(). 260 */ 261 static inline struct srcu_ctr __percpu notrace *__srcu_read_lock_fast(struct srcu_struct *ssp) 262 { 263 struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp); 264 265 if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) 266 this_cpu_inc(scp->srcu_locks.counter); // Y, and implicit RCU reader. 267 else 268 atomic_long_inc(raw_cpu_ptr(&scp->srcu_locks)); // Y, and implicit RCU reader. 269 barrier(); /* Avoid leaking the critical section. */ 270 return scp; 271 } 272 273 /* 274 * Removes the count for the old reader from the appropriate 275 * per-CPU element of the srcu_struct. Note that this may well be a 276 * different CPU than that which was incremented by the corresponding 277 * srcu_read_lock_fast(), but it must be within the same task. 278 * 279 * Please see the __srcu_read_lock_fast() function's header comment for 280 * information on implicit RCU readers and NMI safety. 281 */ 282 static inline void notrace 283 __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp) 284 { 285 barrier(); /* Avoid leaking the critical section. */ 286 if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) 287 this_cpu_inc(scp->srcu_unlocks.counter); // Z, and implicit RCU reader. 288 else 289 atomic_long_inc(raw_cpu_ptr(&scp->srcu_unlocks)); // Z, and implicit RCU reader. 290 } 291 292 void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor); 293 294 // Record reader usage even for CONFIG_PROVE_RCU=n kernels. This is 295 // needed only for flavors that require grace-period smp_mb() calls to be 296 // promoted to synchronize_rcu(). 297 static inline void srcu_check_read_flavor_force(struct srcu_struct *ssp, int read_flavor) 298 { 299 struct srcu_data *sdp = raw_cpu_ptr(ssp->sda); 300 301 if (likely(READ_ONCE(sdp->srcu_reader_flavor) & read_flavor)) 302 return; 303 304 // Note that the cmpxchg() in __srcu_check_read_flavor() is fully ordered. 305 __srcu_check_read_flavor(ssp, read_flavor); 306 } 307 308 // Record non-_lite() usage only for CONFIG_PROVE_RCU=y kernels. 309 static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) 310 { 311 if (IS_ENABLED(CONFIG_PROVE_RCU)) 312 __srcu_check_read_flavor(ssp, read_flavor); 313 } 314 315 #endif 316