1 /* 2 * Read-Copy Update mechanism for mutual exclusion 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License as published by 6 * the Free Software Foundation; either version 2 of the License, or 7 * (at your option) any later version. 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * GNU General Public License for more details. 13 * 14 * You should have received a copy of the GNU General Public License 15 * along with this program; if not, write to the Free Software 16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. 17 * 18 * Copyright (C) IBM Corporation, 2001 19 * 20 * Author: Dipankar Sarma <dipankar (at) in.ibm.com> 21 * 22 * Based on the original work by Paul McKenney <paul.mckenney (at) us.ibm.com> 23 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. 24 * Papers: 25 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf 26 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) 27 * 28 * For detailed explanation of Read-Copy Update mechanism see - 29 * http://lse.sourceforge.net/locking/rcupdate.html 30 * 31 */ 32 33 #ifndef __LINUX_RCUPDATE_H 34 #define __LINUX_RCUPDATE_H 35 36 #ifdef __KERNEL__ 37 38 #include <linux/cache.h> 39 #include <linux/spinlock.h> 40 #include <linux/threads.h> 41 #include <linux/percpu.h> 42 #include <linux/cpumask.h> 43 #include <linux/seqlock.h> 44 45 /** 46 * struct rcu_head - callback structure for use with RCU 47 * @next: next update requests in a list 48 * @func: actual update function to call after the grace period. 49 */ 50 struct rcu_head { 51 struct rcu_head *next; 52 void (*func)(struct rcu_head *head); 53 }; 54 55 #define RCU_HEAD_INIT { .next = NULL, .func = NULL } 56 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT 57 #define INIT_RCU_HEAD(ptr) do { \ 58 (ptr)->next = NULL; (ptr)->func = NULL; \ 59 } while (0) 60 61 62 63 /* Global control variables for rcupdate callback mechanism. */ 64 struct rcu_ctrlblk { 65 long cur; /* Current batch number. */ 66 long completed; /* Number of the last completed batch */ 67 int next_pending; /* Is the next batch already waiting? */ 68 69 spinlock_t lock ____cacheline_internodealigned_in_smp; 70 cpumask_t cpumask; /* CPUs that need to switch in order */ 71 /* for current batch to proceed. */ 72 } ____cacheline_internodealigned_in_smp; 73 74 /* Is batch a before batch b ? */ 75 static inline int rcu_batch_before(long a, long b) 76 { 77 return (a - b) < 0; 78 } 79 80 /* Is batch a after batch b ? */ 81 static inline int rcu_batch_after(long a, long b) 82 { 83 return (a - b) > 0; 84 } 85 86 /* 87 * Per-CPU data for Read-Copy UPdate. 88 * nxtlist - new callbacks are added here 89 * curlist - current batch for which quiescent cycle started if any 90 */ 91 struct rcu_data { 92 /* 1) quiescent state handling : */ 93 long quiescbatch; /* Batch # for grace period */ 94 int passed_quiesc; /* User-mode/idle loop etc. */ 95 int qs_pending; /* core waits for quiesc state */ 96 97 /* 2) batch handling */ 98 long batch; /* Batch # for current RCU batch */ 99 struct rcu_head *nxtlist; 100 struct rcu_head **nxttail; 101 long qlen; /* # of queued callbacks */ 102 struct rcu_head *curlist; 103 struct rcu_head **curtail; 104 struct rcu_head *donelist; 105 struct rcu_head **donetail; 106 long blimit; /* Upper limit on a processed batch */ 107 int cpu; 108 struct rcu_head barrier; 109 #ifdef CONFIG_SMP 110 long last_rs_qlen; /* qlen during the last resched */ 111 #endif 112 }; 113 114 DECLARE_PER_CPU(struct rcu_data, rcu_data); 115 DECLARE_PER_CPU(struct rcu_data, rcu_bh_data); 116 117 /* 118 * Increment the quiescent state counter. 119 * The counter is a bit degenerated: We do not need to know 120 * how many quiescent states passed, just if there was at least 121 * one since the start of the grace period. Thus just a flag. 122 */ 123 static inline void rcu_qsctr_inc(int cpu) 124 { 125 struct rcu_data *rdp = &per_cpu(rcu_data, cpu); 126 rdp->passed_quiesc = 1; 127 } 128 static inline void rcu_bh_qsctr_inc(int cpu) 129 { 130 struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu); 131 rdp->passed_quiesc = 1; 132 } 133 134 extern int rcu_pending(int cpu); 135 extern int rcu_needs_cpu(int cpu); 136 137 /** 138 * rcu_read_lock - mark the beginning of an RCU read-side critical section. 139 * 140 * When synchronize_rcu() is invoked on one CPU while other CPUs 141 * are within RCU read-side critical sections, then the 142 * synchronize_rcu() is guaranteed to block until after all the other 143 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked 144 * on one CPU while other CPUs are within RCU read-side critical 145 * sections, invocation of the corresponding RCU callback is deferred 146 * until after the all the other CPUs exit their critical sections. 147 * 148 * Note, however, that RCU callbacks are permitted to run concurrently 149 * with RCU read-side critical sections. One way that this can happen 150 * is via the following sequence of events: (1) CPU 0 enters an RCU 151 * read-side critical section, (2) CPU 1 invokes call_rcu() to register 152 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, 153 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU 154 * callback is invoked. This is legal, because the RCU read-side critical 155 * section that was running concurrently with the call_rcu() (and which 156 * therefore might be referencing something that the corresponding RCU 157 * callback would free up) has completed before the corresponding 158 * RCU callback is invoked. 159 * 160 * RCU read-side critical sections may be nested. Any deferred actions 161 * will be deferred until the outermost RCU read-side critical section 162 * completes. 163 * 164 * It is illegal to block while in an RCU read-side critical section. 165 */ 166 #define rcu_read_lock() \ 167 do { \ 168 preempt_disable(); \ 169 __acquire(RCU); \ 170 } while(0) 171 172 /** 173 * rcu_read_unlock - marks the end of an RCU read-side critical section. 174 * 175 * See rcu_read_lock() for more information. 176 */ 177 #define rcu_read_unlock() \ 178 do { \ 179 __release(RCU); \ 180 preempt_enable(); \ 181 } while(0) 182 183 /* 184 * So where is rcu_write_lock()? It does not exist, as there is no 185 * way for writers to lock out RCU readers. This is a feature, not 186 * a bug -- this property is what provides RCU's performance benefits. 187 * Of course, writers must coordinate with each other. The normal 188 * spinlock primitives work well for this, but any other technique may be 189 * used as well. RCU does not care how the writers keep out of each 190 * others' way, as long as they do so. 191 */ 192 193 /** 194 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section 195 * 196 * This is equivalent of rcu_read_lock(), but to be used when updates 197 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks 198 * consider completion of a softirq handler to be a quiescent state, 199 * a process in RCU read-side critical section must be protected by 200 * disabling softirqs. Read-side critical sections in interrupt context 201 * can use just rcu_read_lock(). 202 * 203 */ 204 #define rcu_read_lock_bh() \ 205 do { \ 206 local_bh_disable(); \ 207 __acquire(RCU_BH); \ 208 } while(0) 209 210 /* 211 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section 212 * 213 * See rcu_read_lock_bh() for more information. 214 */ 215 #define rcu_read_unlock_bh() \ 216 do { \ 217 __release(RCU_BH); \ 218 local_bh_enable(); \ 219 } while(0) 220 221 /** 222 * rcu_dereference - fetch an RCU-protected pointer in an 223 * RCU read-side critical section. This pointer may later 224 * be safely dereferenced. 225 * 226 * Inserts memory barriers on architectures that require them 227 * (currently only the Alpha), and, more importantly, documents 228 * exactly which pointers are protected by RCU. 229 */ 230 231 #define rcu_dereference(p) ({ \ 232 typeof(p) _________p1 = p; \ 233 smp_read_barrier_depends(); \ 234 (_________p1); \ 235 }) 236 237 /** 238 * rcu_assign_pointer - assign (publicize) a pointer to a newly 239 * initialized structure that will be dereferenced by RCU read-side 240 * critical sections. Returns the value assigned. 241 * 242 * Inserts memory barriers on architectures that require them 243 * (pretty much all of them other than x86), and also prevents 244 * the compiler from reordering the code that initializes the 245 * structure after the pointer assignment. More importantly, this 246 * call documents which pointers will be dereferenced by RCU read-side 247 * code. 248 */ 249 250 #define rcu_assign_pointer(p, v) ({ \ 251 smp_wmb(); \ 252 (p) = (v); \ 253 }) 254 255 /** 256 * synchronize_sched - block until all CPUs have exited any non-preemptive 257 * kernel code sequences. 258 * 259 * This means that all preempt_disable code sequences, including NMI and 260 * hardware-interrupt handlers, in progress on entry will have completed 261 * before this primitive returns. However, this does not guarantee that 262 * softirq handlers will have completed, since in some kernels, these 263 * handlers can run in process context, and can block. 264 * 265 * This primitive provides the guarantees made by the (now removed) 266 * synchronize_kernel() API. In contrast, synchronize_rcu() only 267 * guarantees that rcu_read_lock() sections will have completed. 268 * In "classic RCU", these two guarantees happen to be one and 269 * the same, but can differ in realtime RCU implementations. 270 */ 271 #define synchronize_sched() synchronize_rcu() 272 273 extern void rcu_init(void); 274 extern void rcu_check_callbacks(int cpu, int user); 275 extern void rcu_restart_cpu(int cpu); 276 extern long rcu_batches_completed(void); 277 extern long rcu_batches_completed_bh(void); 278 279 /* Exported interfaces */ 280 extern void FASTCALL(call_rcu(struct rcu_head *head, 281 void (*func)(struct rcu_head *head))); 282 extern void FASTCALL(call_rcu_bh(struct rcu_head *head, 283 void (*func)(struct rcu_head *head))); 284 extern void synchronize_rcu(void); 285 void synchronize_idle(void); 286 extern void rcu_barrier(void); 287 288 #endif /* __KERNEL__ */ 289 #endif /* __LINUX_RCUPDATE_H */ 290
