xref: /openbmc/linux/include/linux/srcutree.h (revision e15a1930)
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_nmi_safety;			/* NMI-safe 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 /*
47  * Node in SRCU combining tree, similar in function to rcu_data.
48  */
49 struct srcu_node {
50 	spinlock_t __private lock;
51 	unsigned long srcu_have_cbs[4];		/* GP seq for children having CBs, but only */
52 						/*  if greater than ->srcu_gp_seq. */
53 	unsigned long srcu_data_have_cbs[4];	/* Which srcu_data structs have CBs for given GP? */
54 	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
55 	struct srcu_node *srcu_parent;		/* Next up in tree. */
56 	int grplo;				/* Least CPU for node. */
57 	int grphi;				/* Biggest CPU for node. */
58 };
59 
60 /*
61  * Per-SRCU-domain structure, update-side data linked from srcu_struct.
62  */
63 struct srcu_usage {
64 	struct srcu_node *node;			/* Combining tree. */
65 	struct srcu_node *level[RCU_NUM_LVLS + 1];
66 						/* First node at each level. */
67 	int srcu_size_state;			/* Small-to-big transition state. */
68 	struct mutex srcu_cb_mutex;		/* Serialize CB preparation. */
69 	spinlock_t __private lock;		/* Protect counters and size state. */
70 	struct mutex srcu_gp_mutex;		/* Serialize GP work. */
71 	unsigned long srcu_gp_seq;		/* Grace-period seq #. */
72 	unsigned long srcu_gp_seq_needed;	/* Latest gp_seq needed. */
73 	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
74 	unsigned long srcu_gp_start;		/* Last GP start timestamp (jiffies) */
75 	unsigned long srcu_last_gp_end;		/* Last GP end timestamp (ns) */
76 	unsigned long srcu_size_jiffies;	/* Current contention-measurement interval. */
77 	unsigned long srcu_n_lock_retries;	/* Contention events in current interval. */
78 	unsigned long srcu_n_exp_nodelay;	/* # expedited no-delays in current GP phase. */
79 	bool sda_is_static;			/* May ->sda be passed to free_percpu()? */
80 	unsigned long srcu_barrier_seq;		/* srcu_barrier seq #. */
81 	struct mutex srcu_barrier_mutex;	/* Serialize barrier ops. */
82 	struct completion srcu_barrier_completion;
83 						/* Awaken barrier rq at end. */
84 	atomic_t srcu_barrier_cpu_cnt;		/* # CPUs not yet posting a */
85 						/*  callback for the barrier */
86 						/*  operation. */
87 	unsigned long reschedule_jiffies;
88 	unsigned long reschedule_count;
89 	struct delayed_work work;
90 	struct srcu_struct *srcu_ssp;
91 };
92 
93 /*
94  * Per-SRCU-domain structure, similar in function to rcu_state.
95  */
96 struct srcu_struct {
97 	unsigned int srcu_idx;			/* Current rdr array element. */
98 	struct srcu_data __percpu *sda;		/* Per-CPU srcu_data array. */
99 	struct lockdep_map dep_map;
100 	struct srcu_usage *srcu_sup;		/* Update-side data. */
101 };
102 
103 // Values for size state variable (->srcu_size_state).  Once the state
104 // has been set to SRCU_SIZE_ALLOC, the grace-period code advances through
105 // this state machine one step per grace period until the SRCU_SIZE_BIG state
106 // is reached.  Otherwise, the state machine remains in the SRCU_SIZE_SMALL
107 // state indefinitely.
108 #define SRCU_SIZE_SMALL		0	// No srcu_node combining tree, ->node == NULL
109 #define SRCU_SIZE_ALLOC		1	// An srcu_node tree is being allocated, initialized,
110 					//  and then referenced by ->node.  It will not be used.
111 #define SRCU_SIZE_WAIT_BARRIER	2	// The srcu_node tree starts being used by everything
112 					//  except call_srcu(), especially by srcu_barrier().
113 					//  By the end of this state, all CPUs and threads
114 					//  are aware of this tree's existence.
115 #define SRCU_SIZE_WAIT_CALL	3	// The srcu_node tree starts being used by call_srcu().
116 					//  By the end of this state, all of the call_srcu()
117 					//  invocations that were running on a non-boot CPU
118 					//  and using the boot CPU's callback queue will have
119 					//  completed.
120 #define SRCU_SIZE_WAIT_CBS1	4	// Don't trust the ->srcu_have_cbs[] grace-period
121 #define SRCU_SIZE_WAIT_CBS2	5	//  sequence elements or the ->srcu_data_have_cbs[]
122 #define SRCU_SIZE_WAIT_CBS3	6	//  CPU-bitmask elements until all four elements of
123 #define SRCU_SIZE_WAIT_CBS4	7	//  each array have been initialized.
124 #define SRCU_SIZE_BIG		8	// The srcu_node combining tree is fully initialized
125 					//  and all aspects of it are being put to use.
126 
127 /* Values for state variable (bottom bits of ->srcu_gp_seq). */
128 #define SRCU_STATE_IDLE		0
129 #define SRCU_STATE_SCAN1	1
130 #define SRCU_STATE_SCAN2	2
131 
132 #define __SRCU_USAGE_INIT(name)									\
133 {												\
134 	.lock = __SPIN_LOCK_UNLOCKED(name.lock),						\
135 	.srcu_gp_seq_needed = -1UL,								\
136 	.work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0),					\
137 }
138 
139 #define __SRCU_STRUCT_INIT_COMMON(name, usage_name)						\
140 	.srcu_sup = &usage_name,								\
141 	__SRCU_DEP_MAP_INIT(name)
142 
143 #define __SRCU_STRUCT_INIT_MODULE(name, usage_name)						\
144 {												\
145 	__SRCU_STRUCT_INIT_COMMON(name, usage_name)						\
146 }
147 
148 #define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name)						\
149 {												\
150 	.sda = &pcpu_name,									\
151 	__SRCU_STRUCT_INIT_COMMON(name, usage_name)						\
152 }
153 
154 /*
155  * Define and initialize a srcu struct at build time.
156  * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
157  *
158  * Note that although DEFINE_STATIC_SRCU() hides the name from other
159  * files, the per-CPU variable rules nevertheless require that the
160  * chosen name be globally unique.  These rules also prohibit use of
161  * DEFINE_STATIC_SRCU() within a function.  If these rules are too
162  * restrictive, declare the srcu_struct manually.  For example, in
163  * each file:
164  *
165  *	static struct srcu_struct my_srcu;
166  *
167  * Then, before the first use of each my_srcu, manually initialize it:
168  *
169  *	init_srcu_struct(&my_srcu);
170  *
171  * See include/linux/percpu-defs.h for the rules on per-CPU variables.
172  */
173 #ifdef MODULE
174 # define __DEFINE_SRCU(name, is_static)								\
175 	static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage);	\
176 	is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage);	\
177 	extern struct srcu_struct * const __srcu_struct_##name;					\
178 	struct srcu_struct * const __srcu_struct_##name						\
179 		__section("___srcu_struct_ptrs") = &name
180 #else
181 # define __DEFINE_SRCU(name, is_static)								\
182 	static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data);				\
183 	static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage);	\
184 	is_static struct srcu_struct name =							\
185 		__SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data)
186 #endif
187 #define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
188 #define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)
189 
190 void synchronize_srcu_expedited(struct srcu_struct *ssp);
191 void srcu_barrier(struct srcu_struct *ssp);
192 void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf);
193 
194 #endif
195