1 /*
2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
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 IBM Corporation, 2008
19 *
20 * Author: Dipankar Sarma <dipankar@in.ibm.com>
21 * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical algorithm
22 *
23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
25 *
26 * For detailed explanation of Read-Copy Update mechanism see -
27 * Documentation/RCU
28 */
29
30 #ifndef __LINUX_RCUTREE_H
31 #define __LINUX_RCUTREE_H
32
33 #include <linux/cache.h>
34 #include <linux/spinlock.h>
35 #include <linux/threads.h>
36 #include <linux/percpu.h>
37 #include <linux/cpumask.h>
38 #include <linux/seqlock.h>
39
40 /*
41 * Define shape of hierarchy based on NR_CPUS and CONFIG_RCU_FANOUT.
42 * In theory, it should be possible to add more levels straightforwardly.
43 * In practice, this has not been tested, so there is probably some
44 * bug somewhere.
45 */
46 #define MAX_RCU_LVLS 3
47 #define RCU_FANOUT (CONFIG_RCU_FANOUT)
48 #define RCU_FANOUT_SQ (RCU_FANOUT * RCU_FANOUT)
49 #define RCU_FANOUT_CUBE (RCU_FANOUT_SQ * RCU_FANOUT)
50
51 #if NR_CPUS <= RCU_FANOUT
52 # define NUM_RCU_LVLS 1
53 # define NUM_RCU_LVL_0 1
54 # define NUM_RCU_LVL_1 (NR_CPUS)
55 # define NUM_RCU_LVL_2 0
56 # define NUM_RCU_LVL_3 0
57 #elif NR_CPUS <= RCU_FANOUT_SQ
58 # define NUM_RCU_LVLS 2
59 # define NUM_RCU_LVL_0 1
60 # define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT - 1) / RCU_FANOUT)
61 # define NUM_RCU_LVL_2 (NR_CPUS)
62 # define NUM_RCU_LVL_3 0
63 #elif NR_CPUS <= RCU_FANOUT_CUBE
64 # define NUM_RCU_LVLS 3
65 # define NUM_RCU_LVL_0 1
66 # define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT_SQ - 1) / RCU_FANOUT_SQ)
67 # define NUM_RCU_LVL_2 (((NR_CPUS) + (RCU_FANOUT) - 1) / (RCU_FANOUT))
68 # define NUM_RCU_LVL_3 NR_CPUS
69 #else
70 # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
71 #endif /* #if (NR_CPUS) <= RCU_FANOUT */
72
73 #define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
74 #define NUM_RCU_NODES (RCU_SUM - NR_CPUS)
75
76 /*
77 * Dynticks per-CPU state.
78 */
79 struct rcu_dynticks {
80 int dynticks_nesting; /* Track nesting level, sort of. */
81 int dynticks; /* Even value for dynticks-idle, else odd. */
82 int dynticks_nmi; /* Even value for either dynticks-idle or */
83 /* not in nmi handler, else odd. So this */
84 /* remains even for nmi from irq handler. */
85 };
86
87 /*
88 * Definition for node within the RCU grace-period-detection hierarchy.
89 */
90 struct rcu_node {
91 spinlock_t lock;
92 unsigned long qsmask; /* CPUs or groups that need to switch in */
93 /* order for current grace period to proceed.*/
94 unsigned long qsmaskinit;
95 /* Per-GP initialization for qsmask. */
96 unsigned long grpmask; /* Mask to apply to parent qsmask. */
97 int grplo; /* lowest-numbered CPU or group here. */
98 int grphi; /* highest-numbered CPU or group here. */
99 u8 grpnum; /* CPU/group number for next level up. */
100 u8 level; /* root is at level 0. */
101 struct rcu_node *parent;
102 } ____cacheline_internodealigned_in_smp;
103
104 /* Index values for nxttail array in struct rcu_data. */
105 #define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */
106 #define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */
107 #define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */
108 #define RCU_NEXT_TAIL 3
109 #define RCU_NEXT_SIZE 4
110
111 /* Per-CPU data for read-copy update. */
112 struct rcu_data {
113 /* 1) quiescent-state and grace-period handling : */
114 long completed; /* Track rsp->completed gp number */
115 /* in order to detect GP end. */
116 long gpnum; /* Highest gp number that this CPU */
117 /* is aware of having started. */
118 long passed_quiesc_completed;
119 /* Value of completed at time of qs. */
120 bool passed_quiesc; /* User-mode/idle loop etc. */
121 bool qs_pending; /* Core waits for quiesc state. */
122 bool beenonline; /* CPU online at least once. */
123 struct rcu_node *mynode; /* This CPU's leaf of hierarchy */
124 unsigned long grpmask; /* Mask to apply to leaf qsmask. */
125
126 /* 2) batch handling */
127 /*
128 * If nxtlist is not NULL, it is partitioned as follows.
129 * Any of the partitions might be empty, in which case the
130 * pointer to that partition will be equal to the pointer for
131 * the following partition. When the list is empty, all of
132 * the nxttail elements point to nxtlist, which is NULL.
133 *
134 * [*nxttail[RCU_NEXT_READY_TAIL], NULL = *nxttail[RCU_NEXT_TAIL]):
135 * Entries that might have arrived after current GP ended
136 * [*nxttail[RCU_WAIT_TAIL], *nxttail[RCU_NEXT_READY_TAIL]):
137 * Entries known to have arrived before current GP ended
138 * [*nxttail[RCU_DONE_TAIL], *nxttail[RCU_WAIT_TAIL]):
139 * Entries that batch # <= ->completed - 1: waiting for current GP
140 * [nxtlist, *nxttail[RCU_DONE_TAIL]):
141 * Entries that batch # <= ->completed
142 * The grace period for these entries has completed, and
143 * the other grace-period-completed entries may be moved
144 * here temporarily in rcu_process_callbacks().
145 */
146 struct rcu_head *nxtlist;
147 struct rcu_head **nxttail[RCU_NEXT_SIZE];
148 long qlen; /* # of queued callbacks */
149 long blimit; /* Upper limit on a processed batch */
150
151 #ifdef CONFIG_NO_HZ
152 /* 3) dynticks interface. */
153 struct rcu_dynticks *dynticks; /* Shared per-CPU dynticks state. */
154 int dynticks_snap; /* Per-GP tracking for dynticks. */
155 int dynticks_nmi_snap; /* Per-GP tracking for dynticks_nmi. */
156 #endif /* #ifdef CONFIG_NO_HZ */
157
158 /* 4) reasons this CPU needed to be kicked by force_quiescent_state */
159 #ifdef CONFIG_NO_HZ
160 unsigned long dynticks_fqs; /* Kicked due to dynticks idle. */
161 #endif /* #ifdef CONFIG_NO_HZ */
162 unsigned long offline_fqs; /* Kicked due to being offline. */
163 unsigned long resched_ipi; /* Sent a resched IPI. */
164
165 /* 5) state to allow this CPU to force_quiescent_state on others */
166 long n_rcu_pending; /* rcu_pending() calls since boot. */
167 long n_rcu_pending_force_qs; /* when to force quiescent states. */
168
169 int cpu;
170 };
171
172 /* Values for signaled field in struct rcu_state. */
173 #define RCU_GP_INIT 0 /* Grace period being initialized. */
174 #define RCU_SAVE_DYNTICK 1 /* Need to scan dyntick state. */
175 #define RCU_FORCE_QS 2 /* Need to force quiescent state. */
176 #ifdef CONFIG_NO_HZ
177 #define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK
178 #else /* #ifdef CONFIG_NO_HZ */
179 #define RCU_SIGNAL_INIT RCU_FORCE_QS
180 #endif /* #else #ifdef CONFIG_NO_HZ */
181
182 #define RCU_JIFFIES_TILL_FORCE_QS 3 /* for rsp->jiffies_force_qs */
183 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
184 #define RCU_SECONDS_TILL_STALL_CHECK (10 * HZ) /* for rsp->jiffies_stall */
185 #define RCU_SECONDS_TILL_STALL_RECHECK (30 * HZ) /* for rsp->jiffies_stall */
186 #define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */
187 /* to take at least one */
188 /* scheduling clock irq */
189 /* before ratting on them. */
190
191 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
192
193 /*
194 * RCU global state, including node hierarchy. This hierarchy is
195 * represented in "heap" form in a dense array. The root (first level)
196 * of the hierarchy is in ->node[0] (referenced by ->level[0]), the second
197 * level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]),
198 * and the third level in ->node[m+1] and following (->node[m+1] referenced
199 * by ->level[2]). The number of levels is determined by the number of
200 * CPUs and by CONFIG_RCU_FANOUT. Small systems will have a "hierarchy"
201 * consisting of a single rcu_node.
202 */
203 struct rcu_state {
204 struct rcu_node node[NUM_RCU_NODES]; /* Hierarchy. */
205 struct rcu_node *level[NUM_RCU_LVLS]; /* Hierarchy levels. */
206 u32 levelcnt[MAX_RCU_LVLS + 1]; /* # nodes in each level. */
207 u8 levelspread[NUM_RCU_LVLS]; /* kids/node in each level. */
208 struct rcu_data *rda[NR_CPUS]; /* array of rdp pointers. */
209
210 /* The following fields are guarded by the root rcu_node's lock. */
211
212 u8 signaled ____cacheline_internodealigned_in_smp;
213 /* Force QS state. */
214 long gpnum; /* Current gp number. */
215 long completed; /* # of last completed gp. */
216 spinlock_t onofflock; /* exclude on/offline and */
217 /* starting new GP. */
218 spinlock_t fqslock; /* Only one task forcing */
219 /* quiescent states. */
220 unsigned long jiffies_force_qs; /* Time at which to invoke */
221 /* force_quiescent_state(). */
222 unsigned long n_force_qs; /* Number of calls to */
223 /* force_quiescent_state(). */
224 unsigned long n_force_qs_lh; /* ~Number of calls leaving */
225 /* due to lock unavailable. */
226 unsigned long n_force_qs_ngp; /* Number of calls leaving */
227 /* due to no GP active. */
228 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
229 unsigned long gp_start; /* Time at which GP started, */
230 /* but in jiffies. */
231 unsigned long jiffies_stall; /* Time at which to check */
232 /* for CPU stalls. */
233 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
234 #ifdef CONFIG_NO_HZ
235 long dynticks_completed; /* Value of completed @ snap. */
236 #endif /* #ifdef CONFIG_NO_HZ */
237 };
238
239 extern struct rcu_state rcu_state;
240 DECLARE_PER_CPU(struct rcu_data, rcu_data);
241
242 extern struct rcu_state rcu_bh_state;
243 DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
244
245 /*
246 * Increment the quiescent state counter.
247 * The counter is a bit degenerated: We do not need to know
248 * how many quiescent states passed, just if there was at least
249 * one since the start of the grace period. Thus just a flag.
250 */
rcu_qsctr_inc(int cpu)251 static inline void rcu_qsctr_inc(int cpu)
252 {
253 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
254 rdp->passed_quiesc = 1;
255 rdp->passed_quiesc_completed = rdp->completed;
256 }
rcu_bh_qsctr_inc(int cpu)257 static inline void rcu_bh_qsctr_inc(int cpu)
258 {
259 struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
260 rdp->passed_quiesc = 1;
261 rdp->passed_quiesc_completed = rdp->completed;
262 }
263
264 extern int rcu_pending(int cpu);
265 extern int rcu_needs_cpu(int cpu);
266
267 #ifdef CONFIG_DEBUG_LOCK_ALLOC
268 extern struct lockdep_map rcu_lock_map;
269 # define rcu_read_acquire() \
270 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
271 # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
272 #else
273 # define rcu_read_acquire() do { } while (0)
274 # define rcu_read_release() do { } while (0)
275 #endif
276
__rcu_read_lock(void)277 static inline void __rcu_read_lock(void)
278 {
279 preempt_disable();
280 __acquire(RCU);
281 rcu_read_acquire();
282 }
__rcu_read_unlock(void)283 static inline void __rcu_read_unlock(void)
284 {
285 rcu_read_release();
286 __release(RCU);
287 preempt_enable();
288 }
__rcu_read_lock_bh(void)289 static inline void __rcu_read_lock_bh(void)
290 {
291 local_bh_disable();
292 __acquire(RCU_BH);
293 rcu_read_acquire();
294 }
__rcu_read_unlock_bh(void)295 static inline void __rcu_read_unlock_bh(void)
296 {
297 rcu_read_release();
298 __release(RCU_BH);
299 local_bh_enable();
300 }
301
302 #define __synchronize_sched() synchronize_rcu()
303
304 #define call_rcu_sched(head, func) call_rcu(head, func)
305
rcu_init_sched(void)306 static inline void rcu_init_sched(void)
307 {
308 }
309
310 extern void __rcu_init(void);
311 extern void rcu_check_callbacks(int cpu, int user);
312 extern void rcu_restart_cpu(int cpu);
313
314 extern long rcu_batches_completed(void);
315 extern long rcu_batches_completed_bh(void);
316
317 #ifdef CONFIG_NO_HZ
318 void rcu_enter_nohz(void);
319 void rcu_exit_nohz(void);
320 #else /* CONFIG_NO_HZ */
rcu_enter_nohz(void)321 static inline void rcu_enter_nohz(void)
322 {
323 }
rcu_exit_nohz(void)324 static inline void rcu_exit_nohz(void)
325 {
326 }
327 #endif /* CONFIG_NO_HZ */
328
329 /* A context switch is a grace period for rcutree. */
rcu_blocking_is_gp(void)330 static inline int rcu_blocking_is_gp(void)
331 {
332 return num_online_cpus() == 1;
333 }
334
335 #endif /* __LINUX_RCUTREE_H */
336