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_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  */
 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  */
 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.
 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.
 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