include/linux/srcutree.h

   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