LXR linux/include/linux/srcutiny.h

   1/* SPDX-License-Identifier: GPL-2.0+ */
   2/*
   3 * Sleepable Read-Copy Update mechanism for mutual exclusion,
   4 *      tiny variant.
   5 *
   6 * Copyright (C) IBM Corporation, 2017
   7 *
   8 * Author: Paul McKenney <paulmck@linux.ibm.com>
   9 */
  10
  11#ifndef _LINUX_SRCU_TINY_H
  12#define _LINUX_SRCU_TINY_H
  13
  14#include <linux/swait.h>
  15
  16struct srcu_struct {
  17        short srcu_lock_nesting[2];     /* srcu_read_lock() nesting depth. */
  18        unsigned short srcu_idx;        /* Current reader array element in bit 0x2. */
  19        unsigned short srcu_idx_max;    /* Furthest future srcu_idx request. */
  20        u8 srcu_gp_running;             /* GP workqueue running? */
  21        u8 srcu_gp_waiting;             /* GP waiting for readers? */
  22        struct swait_queue_head srcu_wq;
  23                                        /* Last srcu_read_unlock() wakes GP. */
  24        struct rcu_head *srcu_cb_head;  /* Pending callbacks: Head. */
  25        struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
  26        struct work_struct srcu_work;   /* For driving grace periods. */
  27#ifdef CONFIG_DEBUG_LOCK_ALLOC
  28        struct lockdep_map dep_map;
  29#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  30};
  31
  32void srcu_drive_gp(struct work_struct *wp);
  33
  34#define __SRCU_STRUCT_INIT(name, __ignored)                             \
  35{                                                                       \
  36        .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq),        \
  37        .srcu_cb_tail = &name.srcu_cb_head,                             \
  38        .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
  39        __SRCU_DEP_MAP_INIT(name)                                       \
  40}
  41
  42/*
  43 * This odd _STATIC_ arrangement is needed for API compatibility with
  44 * Tree SRCU, which needs some per-CPU data.
  45 */
  46#define DEFINE_SRCU(name) \
  47        struct srcu_struct name = __SRCU_STRUCT_INIT(name, name)
  48#define DEFINE_STATIC_SRCU(name) \
  49        static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name)
  50
  51void synchronize_srcu(struct srcu_struct *ssp);
  52
  53/*
  54 * Counts the new reader in the appropriate per-CPU element of the
  55 * srcu_struct.  Can be invoked from irq/bh handlers, but the matching
  56 * __srcu_read_unlock() must be in the same handler instance.  Returns an
  57 * index that must be passed to the matching srcu_read_unlock().
  58 */
  59static inline int __srcu_read_lock(struct srcu_struct *ssp)
  60{
  61        int idx;
  62
  63        idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
  64        WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
  65        return idx;
  66}
  67
  68static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
  69{
  70        synchronize_srcu(ssp);
  71}
  72
  73static inline void srcu_barrier(struct srcu_struct *ssp)
  74{
  75        synchronize_srcu(ssp);
  76}
  77
  78/* Defined here to avoid size increase for non-torture kernels. */
  79static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
  80                                            char *tt, char *tf)
  81{
  82        int idx;
  83
  84        idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1;
  85        pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
  86                 tt, tf, idx,
  87                 data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
  88                 data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])));
  89}
  90
  91#endif
  92