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