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 /*
21 * Per-CPU structure feeding into leaf srcu_node, similar in function
22 * to rcu_node.
23 */
24 struct srcu_data {
25 /* Read-side state. */
26 atomic_long_t srcu_lock_count[2]; /* Locks per CPU. */
27 atomic_long_t srcu_unlock_count[2]; /* Unlocks per CPU. */
28 int srcu_reader_flavor; /* Reader flavor for srcu_struct structure? */
29
30 /* Update-side state. */
31 spinlock_t __private lock ____cacheline_internodealigned_in_smp;
32 struct rcu_segcblist srcu_cblist; /* List of callbacks.*/
33 unsigned long srcu_gp_seq_needed; /* Furthest future GP needed. */
34 unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */
35 bool srcu_cblist_invoking; /* Invoking these CBs? */
36 struct timer_list delay_work; /* Delay for CB invoking */
37 struct work_struct work; /* Context for CB invoking. */
38 struct rcu_head srcu_barrier_head; /* For srcu_barrier() use. */
39 struct srcu_node *mynode; /* Leaf srcu_node. */
40 unsigned long grpmask; /* Mask for leaf srcu_node */
41 /* ->srcu_data_have_cbs[]. */
42 int cpu;
43 struct srcu_struct *ssp;
44 };
45
46 /* Values for ->srcu_reader_flavor. */
47 #define SRCU_READ_FLAVOR_NORMAL 0x1 // srcu_read_lock().
48 #define SRCU_READ_FLAVOR_NMI 0x2 // srcu_read_lock_nmisafe().
49 #define SRCU_READ_FLAVOR_LITE 0x4 // srcu_read_lock_lite().
50
51 /*
52 * Node in SRCU combining tree, similar in function to rcu_data.
53 */
54 struct srcu_node {
55 spinlock_t __private lock;
56 unsigned long srcu_have_cbs[4]; /* GP seq for children having CBs, but only */
57 /* if greater than ->srcu_gp_seq. */
58 unsigned long srcu_data_have_cbs[4]; /* Which srcu_data structs have CBs for given GP? */
59 unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */
60 struct srcu_node *srcu_parent; /* Next up in tree. */
61 int grplo; /* Least CPU for node. */
62 int grphi; /* Biggest CPU for node. */
63 };
64
65 /*
66 * Per-SRCU-domain structure, update-side data linked from srcu_struct.
67 */
68 struct srcu_usage {
69 struct srcu_node *node; /* Combining tree. */
70 struct srcu_node *level[RCU_NUM_LVLS + 1];
71 /* First node at each level. */
72 int srcu_size_state; /* Small-to-big transition state. */
73 struct mutex srcu_cb_mutex; /* Serialize CB preparation. */
74 spinlock_t __private lock; /* Protect counters and size state. */
75 struct mutex srcu_gp_mutex; /* Serialize GP work. */
76 unsigned long srcu_gp_seq; /* Grace-period seq #. */
77 unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */
78 unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */
79 unsigned long srcu_gp_start; /* Last GP start timestamp (jiffies) */
80 unsigned long srcu_last_gp_end; /* Last GP end timestamp (ns) */
81 unsigned long srcu_size_jiffies; /* Current contention-measurement interval. */
82 unsigned long srcu_n_lock_retries; /* Contention events in current interval. */
83 unsigned long srcu_n_exp_nodelay; /* # expedited no-delays in current GP phase. */
84 bool sda_is_static; /* May ->sda be passed to free_percpu()? */
85 unsigned long srcu_barrier_seq; /* srcu_barrier seq #. */
86 struct mutex srcu_barrier_mutex; /* Serialize barrier ops. */
87 struct completion srcu_barrier_completion;
88 /* Awaken barrier rq at end. */
89 atomic_t srcu_barrier_cpu_cnt; /* # CPUs not yet posting a */
90 /* callback for the barrier */
91 /* operation. */
92 unsigned long reschedule_jiffies;
93 unsigned long reschedule_count;
94 struct delayed_work work;
95 struct srcu_struct *srcu_ssp;
96 };
97
98 /*
99 * Per-SRCU-domain structure, similar in function to rcu_state.
100 */
101 struct srcu_struct {
102 unsigned int srcu_idx; /* Current rdr array element. */
103 struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */
104 struct lockdep_map dep_map;
105 struct srcu_usage *srcu_sup; /* Update-side data. */
106 };
107
108 // Values for size state variable (->srcu_size_state). Once the state
109 // has been set to SRCU_SIZE_ALLOC, the grace-period code advances through
110 // this state machine one step per grace period until the SRCU_SIZE_BIG state
111 // is reached. Otherwise, the state machine remains in the SRCU_SIZE_SMALL
112 // state indefinitely.
113 #define SRCU_SIZE_SMALL 0 // No srcu_node combining tree, ->node == NULL
114 #define SRCU_SIZE_ALLOC 1 // An srcu_node tree is being allocated, initialized,
115 // and then referenced by ->node. It will not be used.
116 #define SRCU_SIZE_WAIT_BARRIER 2 // The srcu_node tree starts being used by everything
117 // except call_srcu(), especially by srcu_barrier().
118 // By the end of this state, all CPUs and threads
119 // are aware of this tree's existence.
120 #define SRCU_SIZE_WAIT_CALL 3 // The srcu_node tree starts being used by call_srcu().
121 // By the end of this state, all of the call_srcu()
122 // invocations that were running on a non-boot CPU
123 // and using the boot CPU's callback queue will have
124 // completed.
125 #define SRCU_SIZE_WAIT_CBS1 4 // Don't trust the ->srcu_have_cbs[] grace-period
126 #define SRCU_SIZE_WAIT_CBS2 5 // sequence elements or the ->srcu_data_have_cbs[]
127 #define SRCU_SIZE_WAIT_CBS3 6 // CPU-bitmask elements until all four elements of
128 #define SRCU_SIZE_WAIT_CBS4 7 // each array have been initialized.
129 #define SRCU_SIZE_BIG 8 // The srcu_node combining tree is fully initialized
130 // and all aspects of it are being put to use.
131
132 /* Values for state variable (bottom bits of ->srcu_gp_seq). */
133 #define SRCU_STATE_IDLE 0
134 #define SRCU_STATE_SCAN1 1
135 #define SRCU_STATE_SCAN2 2
136
137 /*
138 * Values for initializing gp sequence fields. Higher values allow wrap arounds to
139 * occur earlier.
140 * The second value with state is useful in the case of static initialization of
141 * srcu_usage where srcu_gp_seq_needed is expected to have some state value in its
142 * lower bits (or else it will appear to be already initialized within
143 * the call check_init_srcu_struct()).
144 */
145 #define SRCU_GP_SEQ_INITIAL_VAL ((0UL - 100UL) << RCU_SEQ_CTR_SHIFT)
146 #define SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE (SRCU_GP_SEQ_INITIAL_VAL - 1)
147
148 #define __SRCU_USAGE_INIT(name) \
149 { \
150 .lock = __SPIN_LOCK_UNLOCKED(name.lock), \
151 .srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL, \
152 .srcu_gp_seq_needed = SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE, \
153 .srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL, \
154 .work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0), \
155 }
156
157 #define __SRCU_STRUCT_INIT_COMMON(name, usage_name) \
158 .srcu_sup = &usage_name, \
159 __SRCU_DEP_MAP_INIT(name)
160
161 #define __SRCU_STRUCT_INIT_MODULE(name, usage_name) \
162 { \
163 __SRCU_STRUCT_INIT_COMMON(name, usage_name) \
164 }
165
166 #define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name) \
167 { \
168 .sda = &pcpu_name, \
169 __SRCU_STRUCT_INIT_COMMON(name, usage_name) \
170 }
171
172 /*
173 * Define and initialize a srcu struct at build time.
174 * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
175 *
176 * Note that although DEFINE_STATIC_SRCU() hides the name from other
177 * files, the per-CPU variable rules nevertheless require that the
178 * chosen name be globally unique. These rules also prohibit use of
179 * DEFINE_STATIC_SRCU() within a function. If these rules are too
180 * restrictive, declare the srcu_struct manually. For example, in
181 * each file:
182 *
183 * static struct srcu_struct my_srcu;
184 *
185 * Then, before the first use of each my_srcu, manually initialize it:
186 *
187 * init_srcu_struct(&my_srcu);
188 *
189 * See include/linux/percpu-defs.h for the rules on per-CPU variables.
190 */
191 #ifdef MODULE
192 # define __DEFINE_SRCU(name, is_static) \
193 static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \
194 is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage); \
195 extern struct srcu_struct * const __srcu_struct_##name; \
196 struct srcu_struct * const __srcu_struct_##name \
197 __section("___srcu_struct_ptrs") = &name
198 #else
199 # define __DEFINE_SRCU(name, is_static) \
200 static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data); \
201 static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \
202 is_static struct srcu_struct name = \
203 __SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data)
204 #endif
205 #define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */)
206 #define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static)
207
208 void synchronize_srcu_expedited(struct srcu_struct *ssp);
209 void srcu_barrier(struct srcu_struct *ssp);
210 void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf);
211
212 /*
213 * Counts the new reader in the appropriate per-CPU element of the
214 * srcu_struct. Returns an index that must be passed to the matching
215 * srcu_read_unlock_lite().
216 *
217 * Note that this_cpu_inc() is an RCU read-side critical section either
218 * because it disables interrupts, because it is a single instruction,
219 * or because it is a read-modify-write atomic operation, depending on
220 * the whims of the architecture.
221 */
__srcu_read_lock_lite(struct srcu_struct * ssp)222 static inline int __srcu_read_lock_lite(struct srcu_struct *ssp)
223 {
224 int idx;
225
226 RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite().");
227 idx = READ_ONCE(ssp->srcu_idx) & 0x1;
228 this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter); /* Y */
229 barrier(); /* Avoid leaking the critical section. */
230 return idx;
231 }
232
233 /*
234 * Removes the count for the old reader from the appropriate
235 * per-CPU element of the srcu_struct. Note that this may well be a
236 * different CPU than that which was incremented by the corresponding
237 * srcu_read_lock_lite(), but it must be within the same task.
238 *
239 * Note that this_cpu_inc() is an RCU read-side critical section either
240 * because it disables interrupts, because it is a single instruction,
241 * or because it is a read-modify-write atomic operation, depending on
242 * the whims of the architecture.
243 */
__srcu_read_unlock_lite(struct srcu_struct * ssp,int idx)244 static inline void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
245 {
246 barrier(); /* Avoid leaking the critical section. */
247 this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter); /* Z */
248 RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_lite().");
249 }
250
251 void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
252
253 // Record _lite() usage even for CONFIG_PROVE_RCU=n kernels.
srcu_check_read_flavor_lite(struct srcu_struct * ssp)254 static inline void srcu_check_read_flavor_lite(struct srcu_struct *ssp)
255 {
256 struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);
257
258 if (likely(READ_ONCE(sdp->srcu_reader_flavor) & SRCU_READ_FLAVOR_LITE))
259 return;
260
261 // Note that the cmpxchg() in srcu_check_read_flavor() is fully ordered.
262 __srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
263 }
264
265 // Record non-_lite() usage only for CONFIG_PROVE_RCU=y kernels.
srcu_check_read_flavor(struct srcu_struct * ssp,int read_flavor)266 static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor)
267 {
268 if (IS_ENABLED(CONFIG_PROVE_RCU))
269 __srcu_check_read_flavor(ssp, read_flavor);
270 }
271
272 #endif
273